JP2006291175A - Blue light-emitting phosphor dispersed with semiconductor nanoparticles - Google Patents

Abstract

Disclosed are a blue light emitting semiconductor nanoparticle having high light emission efficiency in an aqueous solution and a method for producing the same, and a phosphor having high light emission efficiency obtained by holding the blue light emitting semiconductor nanoparticle in a glass matrix and a method for producing the same. .
Group II-IV semiconductor nanoparticles, such as cadmium sulfide and zinc selenide, having a light emission peak in the wavelength range of 400 to 500 nanometers and a light emission efficiency of 35% or more when dispersed in water. The semiconductor nanoparticles are produced by irradiating ultraviolet light with a group II element-containing water-soluble compound and a group IV element compound dispersed aqueous solution having a pH of 9.5 to 11.5. Furthermore, the phosphor dispersed in the glass matrix can be obtained by dispersing the semiconductor nanoparticles in the glass matrix by a sol-gel method using organoalkoxysilane.
[Selection figure] None

Description

  The present invention relates to blue-emitting semiconductor nanoparticles, a phosphor in which the semiconductor nanoparticles are dispersed, a method for producing the same, and a light-emitting device using the phosphor.

  Semiconductor nanoparticles have been studied for their use as a new type of phosphor. Due to the so-called quantum size effect, the semiconductor nanoparticles exhibit light emission on the short wavelength side because the band gap increases as the particle size decreases, even if they are made of the same material. Such semiconductor nanoparticles are produced today by a colloidal method, and are divided into two types: production in an aqueous solution and production in an organic solution.

Cadmium telluride is known as a typical product prepared in an aqueous solution, and a luminous efficiency of about 60% can be obtained by recent improvements (Patent Document 1 and Non-Patent Document 1). . However, the emission color ranges from green to red, and it is difficult to emit blue or purple light having a wavelength of 500 nanometers or less. One reason is that, in short-wavelength light emission, the energy of excitons generally increases and is easily deactivated. Non-Patent Document 2 reports that a blue-light-emitting cadmium telluride nanoparticle-dispersed aqueous solution is obtained, but this method is difficult to reproduce and the light-emitting efficiency in the blue region is about 20%.

  On the other hand, with respect to a production method using an organic solution, a method of producing semiconductor nanoparticles by thermally decomposing an organic metal is well known (Non-patent Document 3). Cadmium selenide is a typical product produced by this method, and many studies have been conducted. This synthesis requires expensive and complicated experimental equipment, and safety considerations are indispensable, but the surface is covered with zinc sulfide, etc., so that the luminous efficiency is from blue to red (wavelength 470-620 nanometers). About 30-50% can be obtained.

  However, the produced semiconductor nanoparticles cannot be dispersed in water as they are. Whether the semiconductor nanoparticles can be stably dispersed in water while maintaining the luminous efficiency is important for application. For example, when used as a fluorescent marker for biological material, it is indispensable to disperse in water, and when it is fixed to a transparent matrix, the number of types of matrix that can be used increases if it can be dispersed in water. Therefore, in the case of cadmium selenide produced by the above method, many ideas have been made to disperse in water.

  Patent documents 2 and 3 are mentioned as the compilation. This describes that the semiconductor nanoparticles after fabrication can be dispersed in water by treating them with a surfactant such as thiol, and the maximum luminous efficiency is about 18%. Yes.

Recently, research has progressed, and in Non-Patent Document 4, by irradiating the aqueous solution of zinc selenide nanoparticles after fabrication with light, nanoparticles with an emission peak wavelength of about 370 nm and emission efficiency of 25-30% are obtained. It has been reported that. However, this has moved too far to the short wavelength side, and the emission peak wavelength is not within the range felt by the human eye. Also, the luminous efficiency is not sufficient.

Furthermore, Non-Patent Document 5 reports that nanoparticles having an emission peak wavelength of around 470 nanometers can be obtained by using an appropriate amount of thioglycerol as a surfactant in an aqueous solution of zinc selenide nanoparticles. However, the luminous efficiency was as low as about 10%.

By the way, the produced semiconductor nanoparticles are unstable as an aqueous solution or dispersion, and are not suitable for industrial applications. For this reason, if the semiconductor nanoparticles after fabrication can be held and stabilized in a solid matrix, particularly glass, with high luminous efficiency, the technical significance is great.
International Publication No. 2004/65296 Pamphlet International Publication No. 2000/17655 Pamphlet International Publication No. 2000/17656 Pamphlet Lee, Murase, Chemistry Letters, 34, 92 (2005) Raj et al., Journal of Physical Chemistry, Vol. 97, 11999 (1993)) Bavendy et al., Journal of Physical Chemistry B, 101, 9463 (1997) Alexei Shovel et al., Journal of Physical Chemistry B, 108, 5905 (2004) Murase et al., Material Letters, 58, 3898 (2004)

  The present invention has been made in view of the current state of the prior art as described above, and its main object is to provide blue light emitting semiconductor nanoparticles having high luminous efficiency in an aqueous solution and a method for producing the same. Another object of the present invention is to provide a phosphor having a high luminous efficiency obtained by holding the blue light emitting semiconductor nanoparticles in a glass matrix and a method for producing the same.

  The inventor conducted intensive studies to achieve the above-described object, and obtained the following knowledge.

  The first finding is as follows. After preparing an aqueous solution of zinc selenide nanoparticles, the post-treatment to grow the particles by irradiating the zinc selenide nanoparticles with ultraviolet light under the condition of controlling the amount and pH of the surfactant, the human eye It was found that blue light-emitting semiconductor nanoparticles having a light emission peak in the wavelength range of 400 to 500 nanometers that feels blue and having high light emission efficiency in water can be obtained.

The second finding is that a group II element having a larger atomic weight than zinc and / or a group VI element having a larger atomic weight than selenium are added to the inside of the zinc selenide nanoparticles before irradiation with ultraviolet light. As a result, the inventors have found that the emission peak wavelength of the obtained II-VI group semiconductor nanoparticles shifts to a long wavelength. The semiconductor nanoparticles as a whole are composed of elements having a larger atomic weight than zinc selenide. As shown in FIG. 1, generally, in II-VI group semiconductors, it is known that the larger the atomic weight of a constituent element, the narrower the band gap of the semiconductor. As a result, it is considered that the emission peak wavelength of the semiconductor nanoparticles has shifted to a long wavelength.

The third finding is obtained by adding a group II element having a larger atomic weight than zinc and / or a group VI element having a larger atomic weight than selenium to the aqueous solution used when the ultraviolet light irradiation is performed. We found that the emission peak wavelength of II-VI group semiconductor nanoparticles shifts to longer wavelengths. When ultraviolet light irradiation is performed under such conditions, the surface of the semiconductor nanoparticles is coated with a compound of an element having a large atomic weight according to the relationship shown in FIG. 1, and as a result, the emission peak wavelength of the semiconductor nanoparticles. Is considered to have moved to a longer wavelength.

Fourth, when the above third and fourth findings are combined, that is, nanoparticles having zinc selenide as a main component synthesized in advance by adding an element having a large atomic weight in an aqueous solution containing the element having a large atomic weight. It was found that the emission peak wavelength of the obtained II-VI group semiconductor nanoparticles shifts to a longer wavelength when ultraviolet light irradiation is carried out at 1. This is a state where an element having a large atomic weight is added both inside and on the surface of the semiconductor nanoparticle, and as a result of such a synergistic effect, the band gap of the semiconductor nanoparticle becomes narrower, and the emission peak of the semiconductor nanoparticle. It is considered that the wavelength has moved to a longer wavelength.

  Furthermore, it has also been found that a phosphor having high luminous efficiency can be obtained by holding the blue light emitting semiconductor nanoparticles obtained as described above in a glass matrix under predetermined conditions. As a result of further research based on this knowledge, the present invention has been completed.

  That is, the present invention provides the following blue light emitting semiconductor nanoparticles, phosphors, and methods for producing them.

  Item 1. Semiconductor nanoparticles having an emission peak in the wavelength range of 400 to 500 nanometers and an emission efficiency of 35% or more when dispersed in water.

  Item 2. Item 2. The semiconductor nanoparticles according to Item 1, wherein the luminous efficiency when dispersed in water is 45% or more.

Item 3. Item 3. The semiconductor nanoparticles according to Item 1 or 2, wherein the semiconductor nanoparticles are II-VI group semiconductor nanoparticles.

Item 4. Item 4. The semiconductor nanoparticles according to Item 3, wherein the semiconductor nanoparticles are II-VI group semiconductor nanoparticles containing at least one selected from the group consisting of cadmium sulfide, zinc selenide, cadmium selenide, and zinc telluride.

  Item 5. Item 4. The semiconductor nanoparticles according to Item 3, wherein the semiconductor nanoparticles are zinc selenide.

Item 6. Item 4. The semiconductor nanoparticles according to Item 3, wherein the semiconductor nanoparticles are II-VI group semiconductor nanoparticles containing two or more selected from the group consisting of cadmium sulfide, zinc selenide, cadmium selenide, and zinc telluride.

  Item 7. Item 4. The semiconductor nanoparticles according to Item 3, wherein the semiconductor nanoparticles are Group II-VI semiconductor nanoparticles containing two or more Group II elements and / or two or more Group VI elements.

  Item 8. In addition to zinc selenide, the semiconductor nanoparticles include a group II-VI semiconductor containing at least one selected from the group consisting of a group II element having a larger atomic weight than zinc and a group VI element having a larger atomic weight than selenium. Item 4. The semiconductor nanoparticle according to item 3, which is a nanoparticle.

  Item 9. Item 4. The semiconductor nanoparticles according to Item 3, wherein the semiconductor nanoparticles contain cadmium and / or tellurium in addition to zinc selenide.

Item 10. A method for producing a II-VI group semiconductor nanoparticle according to claim 3, comprising (1) II
A group VI element compound is introduced into an aqueous solution having a pH of 6 to 7 in which a water-soluble compound containing a group element and a surfactant are dissolved to produce a dispersed aqueous solution of II-VI semiconductor nanoparticles. (2) Thereafter, the aqueous dispersion of the II-VI group semiconductor nanoparticles is adjusted to pH 9.5 to 11.5, and this is irradiated with ultraviolet light.

  Item 11. Item 11. The production method according to Item 10, wherein the water-soluble compound containing a Group II element in (1) is a mixture of two or more water-soluble compounds having different Group II elements.

  Item 12. Item 12. The production method according to Item 10 or 11, wherein the Group VI element compound in (1) is a mixture of two or more Group VI element compounds having different Group VI elements.

Item 13. Item 13. The production method according to any one of Items 10 to 12, wherein a Group II element and / or Group VI element is further added to the aqueous dispersion of the Group II-VI semiconductor nanoparticles in (2), followed by ultraviolet irradiation. .

Item 14. In the above (1), the II group element of the water-soluble compound containing the II group element is zinc, and the VI group element of the VI group element compound is selenium. In the above (2), the II-VI group semiconductor (selenated) Item 10: At least one selected from the group consisting of a group II element having a larger atomic weight than zinc and a group VI element having a larger atomic weight than selenium is added to the aqueous solution of zinc) nanoparticles, and then irradiated with ultraviolet light The manufacturing method as described in.

  Item 15. Item 15. The method according to Item 14, wherein the Group II element having a larger atomic weight than zinc is cadmium.

  Item 16. Item 15. The method according to Item 14, wherein the Group VI element having a larger atomic weight than selenium is tellurium.

  Item 17. A phosphor in which semiconductor nanoparticles with a light emission peak in the wavelength range of 400 to 500 nanometers and a light emission efficiency of 20% or more are dispersed in a glass matrix.

  Item 18. Item 18. The phosphor according to Item 17, wherein semiconductor nanoparticles having a luminous efficiency of 30% or more are dispersed.

  Item 19. Item 19. The phosphor according to Item 17 or 18 produced using organoalkoxysilane.

Item 20. Item 20. The phosphor according to Item 17, 18 or 19, wherein the semiconductor nanoparticles are II-VI group semiconductor nanoparticles.

Item 21. Item 20. The phosphor according to Item 17, 18 or 19, wherein the semiconductor nanoparticles are II-VI group semiconductor nanoparticles containing at least one selected from the group consisting of cadmium sulfide, zinc selenide, cadmium selenide and zinc telluride.

  Item 22. Item 20. The phosphor according to Item 17, 18 or 19, wherein the semiconductor nanoparticles are II-VI group semiconductor nanoparticles containing two or more group II elements and / or two or more group VI elements.

  Item 23. Item 18. A method for producing a phosphor according to Item 17, wherein the semiconductor nanoparticles according to any one of Items 1 to 9 are dispersed in a glass matrix by a sol-gel method using an organoalkoxysilane. .

As used herein, “emission efficiency of semiconductor nanoparticles in solution” is the ratio of the number of photons (Φ _PL ) emitted as photoluminescence to the number of photons (Φ _A ) absorbed. It is defined as (Φ _PL / Φ _A ). This luminous efficiency is a value that is used as standard in this technical field, and is synonymous with “internal quantum yield”. Luminous efficiency is calculated by using a dye molecule having a known luminous efficiency and comparing the absorbance at the excitation light wavelength and the emission intensity in the dye molecule solution and the measurement object. At the time of measurement, comparison is usually made by matching the absorbance at the excitation wavelength of the dye molecule solution and the measurement object. (See, for example, previously reported methods, Dawson et al., Journal of Physical Chemistry, 72, 3251 (1968)).

In the present specification, “the luminous efficiency of the semiconductor nanoparticles in the phosphor” refers to the photon number (Φ _A ) of excitation light absorbed by the semiconductor nanoparticles in the phosphor. It is defined as the ratio (Φ _A / Φ _PL ) of the number of photons (Φ _PL ) emitted as photoluminescence from the nanoparticles. Specifically, a glass cell containing a dye molecule solution with known absorbance and luminous efficiency, and a glass serving as a measurement object having the same thickness are prepared, and the absorbance in the dye molecule solution and the measurement object is determined. It is a value calculated by comparing the emission intensity.

The present invention is described in detail below.
I. Semiconductor nanoparticles
I-1. Semiconductor nanoparticles prepared by controlling the amount of surfactant and pH and irradiating light The semiconductor nanoparticles of the present invention have water dispersibility, show blue luminescence when irradiated with excitation light, and emit light in an aqueous solution. Semiconductor nanoparticles exhibiting efficiency. In other words, it is a semiconductor nanoparticle having a light emission peak in the wavelength range of 400 to 500 nanometers and a light emission efficiency of 35% or more (particularly 45% or more) when dispersed in water.

Specific examples include II-VI group compound semiconductors that exhibit direct transition and emit light in the blue region. For example, cadmium sulfide, zinc selenide, cadmium selenide, zinc telluride and the like can be exemplified. Zinc selenide is preferable. The semiconductor nanoparticles of the present invention are usually present in a stabilized state in an aqueous solution containing a surfactant.

The semiconductor nanoparticles of the present invention can be produced, for example, as follows. An aqueous solution of II-VI group semiconductor nanoparticles was prepared by introducing a VI group element compound in an aqueous solution having a pH of about 6-7 in which a water-soluble compound containing a group II element and a surfactant were dissolved. Then, the semiconductor nanoparticles of the present invention can be produced by irradiating the aqueous solution of the II-VI group semiconductor nanoparticles with ultraviolet light at pH 10.5 to 12.

  As the water-soluble compound containing a group II element, a perchlorate is preferable. For example, when the group II element is zinc, zinc perchlorate can be used. The concentration of the water-soluble compound containing a group II element in the aqueous solution is usually about 0.001 to 0.05 mol / liter, more preferably about 0.01 to 0.02 mol / liter, particularly 0.012 to 0.018. It is preferably about mol / liter.

  As the group VI element compound, for example, a hydride of a group VI element can be used, and when the group VI element is selenium, hydrogen selenide can be used. Hydrogen selenide can be produced, for example, from aluminum selenide and sulfuric acid. In addition, it is also possible to use it as an aqueous solution of sodium hydrogen selenide obtained by reacting hydrogen selenide with sodium hydroxide. The amount of the group VI element compound used is usually preferably about 0.3 to 1.5 moles, more preferably about 0.4 to 0.9 moles of group VI ions with respect to 1 mole of group II ions.

  As the surfactant, those having a thiol group which is a hydrophobic group and a hydrophilic group are preferable. Examples of the hydrophilic group include an anionic group such as a carboxyl group, a cationic group such as an amino group, and a hydroxyl group, and an anionic group such as a carboxyl group is particularly preferable. Specific examples of this surfactant include thioglycolic acid, thioglycerol, mercaptoethylamine, and the like. The usage-amount of surfactant should just be about 1-5 mol by mole ratio with respect to 1 mol of group II elements contained in aqueous solution, and also about 1.5-3.5 mol. When the usage-amount of surfactant exceeds the said range, there exists a tendency for the luminous efficiency of the ultrafine particle obtained to fall. If the amount is less than the above range, the light emission efficiency is lowered. This is considered to be because the ultrafine particles tend to aggregate when the amount of the surfactant used is too small.

  The water used for the production of the semiconductor nanoparticles is preferably high-purity water. In particular, it is more preferable to use ultrapure water having a specific resistance of 18 MΩ · cm or more and a total amount (TOC) of organic compounds in water of 5 ppb or less, preferably 3 ppb or less. By sufficiently washing the reaction vessel and the like with such high-purity water and using high-purity water as the reaction solvent, it is possible to obtain semiconductor ultrafine particles having excellent light-emitting performance.

  The above reaction is usually carried out by bubbling a gaseous group VI element compound in an aqueous solution in which a water-soluble compound containing a group II element and a surfactant are dissolved in an inert atmosphere, or by adding a gaseous group VI compound. The reaction can be carried out by reacting with a sodium hydroxide solution to make an aqueous solution and then injecting it into an aqueous solution in which a water-soluble compound containing a group II element and a surfactant are dissolved with a syringe or the like.

  The inert atmosphere may be a gas atmosphere that does not participate in the reaction. For example, an inert gas atmosphere such as argon gas, nitrogen gas, and helium gas can be suitably used.

  The above reaction can usually be performed at room temperature (for example, about 10 to 30 ° C.). The pH of the aqueous solution is preferably about 6 to 7, and particularly preferably about 6.2 to 6.8. The reaction is usually completed within about 10 minutes after introducing the group VI compound.

Then, the semiconductor nanoparticle dispersion aqueous solution of desired size is obtained by recirculating | refluxing in air | atmosphere. The concentration of the nanoparticles in the dispersion solution but is appropriately selected depending on the reaction conditions, generally from 1 × 10 ^-4 mol / liter from 5 × 10 ^-6 mol / l, typically 1 × 10 ^{- From 5} mol / liter to about 5 × 10 ⁻⁵ mol / liter, in particular, about 3 × 10 ⁻⁵ mol / liter.

The particle size of the manufactured semiconductor nanoparticles is usually about 2 to 5 nm. Increasing the reflux time can increase the particle size. In order to obtain nanoparticles emitting in a single color, the reflux time is controlled to be constant, and the standard deviation of the dispersion of the particle size distribution is 20% or less, preferably 15% or less with respect to the average value of the particle size. You just have to make adjustments.

  The aqueous dispersion of semiconductor nanoparticles obtained in this manner usually contains Group II element ions, surfactants, fine clusters of less than 1 nanometer, etc. used as raw materials. This dispersed aqueous solution of semiconductor nanoparticles is subjected to ultraviolet light irradiation described later. Note that the luminous efficiency of the semiconductor nanoparticles in this dispersed aqueous solution is as low as about 0 to 0.1%.

  Alternatively, after the nanoparticles contained in the dispersed aqueous solution after reflux are separated into nanoparticles having a uniform particle size, the nanoparticles are redispersed in an aqueous solution containing a group II ion and a surfactant, and ultraviolet light described later. Can be used for irradiation. In this case, it is preferable to select nanoparticles with high luminous efficiency rather than subjecting the aqueous dispersion of semiconductor nanoparticles after refluxing to ultraviolet light irradiation as it is.

For example, using the fact that the solubility decreases as the particle size of the nanoparticles increases, by adding a poor solvent such as isopropanol to the aqueous dispersion of the nanoparticles, the nanoparticles are precipitated according to size and centrifuged. Separation and purification in a vessel. The purified nanoparticles are redispersed in water to form an aqueous solution. The dispersion aqueous solution is stable to some extent as it is, but by adding a water-soluble compound containing a group II element and a surfactant to the dispersion aqueous solution, the stability of the dispersion aqueous solution can be improved and aggregation can be achieved. Can be prevented. The type of the group II element compound, the concentration of the compound, the amount of the surfactant, the pH of the aqueous dispersion, etc. may be adjusted in the same range as the aqueous solution used for preparing the above-mentioned II-VI semiconductor ultrafine particles. .

Specifically, II-VI group semiconductor nanoparticles (about 5 × 10 ^{−6 to} 1.5 × 10 ⁻⁴ mol / liter, preferably about 1 × 10 ^{−5 to} 1.2 × 10 ⁻⁴ mol / liter, more preferably 2 × 10 ^{−5 to} 6 × 10 ⁻⁵ mol / liter), a group II element ion (0.04 to 0.
About 3 mol / liter, preferably about 0.06 to 0.15 mol / liter) and surfactant (about 1.5 to 3.5 mol, preferably 1 mol of group II element ions contained in the aqueous solution, An aqueous solution containing about 2.2 to 2.8 moles) is preferred.

In particular, when the II-VI group semiconductor nanoparticles are zinc selenide nanoparticles, it is preferable to use zinc perchlorate as a water-soluble compound containing a group II element and thioglycolic acid as a surfactant.

  The semiconductor nanoparticles obtained by the above method have good water dispersibility and are almost monodispersed. The luminous efficiency of the semiconductor nanoparticles in this dispersed aqueous solution is still very low, about 0 to 0.1%.

Subsequently, the aqueous solution of the II-VI group semiconductor nanoparticles obtained above is adjusted to pH 9.5 to 11.5 and irradiated with ultraviolet light to produce the semiconductor nanoparticles of the present invention.

The aqueous solution of group II-VI semiconductor nanoparticles is an aqueous solution of semiconductor nanoparticles after reflux, as described above, and an aqueous solution re-dispersed in an aqueous solution containing group II ions and a surfactant after separation and purification of the semiconductor nanoparticles. Any of them may be used. Preferably, it is an aqueous solution in which the semiconductor nanoparticles are redispersed. The aqueous solution contains II-VI semiconductor nanoparticles (5 × 10 ^{−6 to} 1.5 × 10 ⁻⁴ mol /
About 1 liter, preferably about 1 × 10 ^{−5 to} 1.2 × 10 ⁻⁴ mol / liter, more preferably about 2 × 10 ^{−5 to} 6 × 10 ⁻⁵ mol / liter), group II element ions (0.04 to About 0.3 mol / liter, preferably about 0.06 to 0.15 mol / liter) and surfactant (about 1.5 to 3.5 mol with respect to 1 mol of group II element ions contained in the aqueous solution) Preferably about 2.2 to 2.8 mol).

  In particular, prior to the irradiation with ultraviolet light, the pH of the aqueous solution should be about 9.5 to 11.5 (preferably about 10.5 to 11.4, more preferably 10.7 to 11.3). is important. If the pH of the aqueous solution is within this range, the size of the semiconductor nanoparticles is suitably grown by irradiation with ultraviolet light. The luminous intensity and luminous efficiency when irradiated are also increased. On the other hand, if the pH is smaller than this range, the wavelength of the emission peak is less than 400 nanometers, the light in the visible region is reduced, the emission intensity when irradiated with ultraviolet light for a certain period of time is significantly reduced, and the luminous efficiency descend. On the other hand, if the pH is larger than this range, a new defect is generated on the surface of the nanoparticle and the luminous efficiency is lowered. Specifically, it can be easily understood by looking at FIGS. 3 and 4 of Test Example 1 of Example 1. FIG.

A method for making the aqueous solution of II-VI group semiconductor nanoparticles alkaline may be prepared, for example, by adding sodium hydroxide, potassium hydroxide or the like so as to have a pH in the above range.

Irradiation of the above-mentioned aqueous solution of semiconductor nanoparticles with ultraviolet light usually uses light having a wavelength of about 300 to 380 nanometers (preferably about 365 nanometers) for about 30 to 200 minutes (preferably about 50 to 180 minutes). Irradiation is preferred. By irradiating the aqueous solution of semiconductor nanoparticles with light having such an appropriate wavelength, high luminous efficiency and luminous intensity are achieved. This is considered to be because the repair of the nanoparticle surface defects by the surfactant is promoted by irradiation with ultraviolet light. Moreover, if the irradiation time is about 30 to 200 minutes, if it is too short, the light emission efficiency and light emission intensity will not increase,
This is because if the length is too long, precipitation occurs due to aggregation of the nanoparticles, which is not preferable.

The irradiation intensity is preferably 50~1000mW / cm ² about (preferably 200~300mW / cm ² or so). Thus, it is considered that by relatively strengthening the light irradiation, the repair of the nanoparticle surface defects can be promoted to prevent the aggregation of the nanoparticles.

Examples of the excitation light source include a xenon lamp, a high-pressure mercury lamp, and an ultraviolet LED.
A high-pressure mercury lamp is preferable. In particular, it is preferable to selectively irradiate light of only 365 nm with ultraviolet light from a high-pressure mercury lamp.

  By irradiating with ultraviolet light under such conditions, an aqueous solution of semiconductor nanoparticles having a light emission peak in the wavelength range of 400 to 500 nanometers and a light emission efficiency of 35% or more, further 40% or more, particularly 40 to 55% is obtained. It is done. Moreover, the diameter of the semiconductor nanoparticles is usually about 2 to 5 nanometers. In particular, in the case of nanoparticles of zinc selenide, such an effect is remarkable.

Moreover, it is also possible to move the emission wavelength of the semiconductor nanoparticles to the longer wavelength side by heating at the time of light irradiation of the aqueous solution of the semiconductor nanoparticles. For example, when the temperature of an aqueous solution of semiconductor nanoparticles (23 ° C.) is increased to 40 ° C. and light irradiation is performed, the emission wavelength is shifted to around 430 nanometers. This is interpreted as the heating promoted the decomposition of thioglycolic acid on the surface of the semiconductor nanoparticles and accelerated the growth of the nanoparticles. Therefore, the temperature at the time of light irradiation to the aqueous solution of semiconductor nanoparticles can be suitably selected from about 15 to 90 ° C., particularly from about 20 to 80 ° C.

In addition, the semiconductor nanoparticles of the present invention exhibit remarkable operational effects that are not heretofore present in that they have the above-mentioned light emission characteristics without doping the nanoparticles with rare earths or transition metal ions. In general, in semiconductor nanoparticles doped with rare earth or transition metal ions, light emission from doped rare earth or transition metal ions is observed, and the decay time of light emission is very slow in the range of milliseconds to microseconds. On the other hand, in the case of the undoped semiconductor nanoparticles of the present invention, the emission decay time is typically as fast as about 10 nanoseconds. different. In the semiconductor nanoparticles of the present invention, the decay time is short, and the luminance increases without saturation as the excitation light increases.
I-2.2 Group II-VI semiconductor nanoparticles containing two or more Group II elements and / or two or more Group VI elements
Child Group II-VI semiconductor nanoparticles of the present invention, two or more Group II elements and / or two or more Group VI element may contain therein. Examples of the II-VI group semiconductor constituting the II-VI group semiconductor nanoparticles include two or more selected from the group consisting of cadmium sulfide, zinc selenide, cadmium selenide and zinc telluride. In the II-VI group semiconductor nanoparticles, the emission peak wavelength varies as compared with the single-group II-VI group semiconductor nanoparticles.

This II-VI group semiconductor nanoparticle is a water-soluble compound containing a group II element in the step of synthesizing the semiconductor nanoparticles described in section I-1 above. And / or as a group VI element compound, a mixture of two or more group VI element compounds having different group VI elements is used.

An example of II-VI group semiconductor nanoparticles mainly composed of zinc selenide will be described below in detail.

For example, in II-VI group semiconductor nanoparticles containing zinc selenide and cadmium selenide, the fluorescence peak wavelength shifts to a longer wavelength side than zinc selenide nanoparticles, and also includes II containing zinc selenide and zinc telluride. In the -VI group semiconductor nanoparticles, the emission peak wavelength shifts to the longer wavelength side than the zinc selenide nanoparticles. That is, since the atomic weight of the elements constituting the nanoparticles is increased, the band gap of the semiconductor is narrowed, and the emission peak wavelength shifts to a long wavelength.

Such II-VI group semiconductor nanoparticles use zinc selenide as semiconductor nanoparticles before irradiation with ultraviolet light, and have a group II element (for example, cadmium) having a larger atomic weight than zinc and / or than selenium. It can be prepared by adding a group VI element having a large atomic weight (for example, tellurium).

  In order to synthesize semiconductor nanoparticles containing a group II element having a larger atomic weight than zinc, in the step of synthesizing semiconductor nanoparticles described in the above section 1-1, for example, in addition to zinc perchlorate, perchlorine What mixed with cadmium acid may be used. In order to move the emission peak wavelength of the nanoparticles to a long wavelength, the addition rate (mol%) of cadmium represented by [amount of cadmium ion] / ([amount of zinc ion] + [amount of cadmium ion]) is 0.3. ˜50%, preferably about 5-25%. Semiconductor nanoparticles obtained by reacting this with hydrogen selenide are those in which cadmium selenide is mixed in zinc selenide.

  Subsequently, the semiconductor nanoparticles of the present invention are obtained by irradiating the semiconductor nanoparticles with ultraviolet light. The emission peak wavelength of the produced semiconductor nanoparticles moves to a longer wavelength than that of the zinc selenide nanoparticles, and is in the range felt by the human eye. Specifically, Example 4 may be referred to.

In addition, in order to synthesize semiconductor nanoparticles containing a Group VI element having a larger atomic weight than selenium, in the process of synthesizing semiconductor nanoparticles described in Section I-1, for example, in addition to hydrogen selenide gas, What mixed hydrogen telluride gas may be used. The tellurium addition ratio (mol%) represented by [tellurium ion amount] / ([selenium ion amount] + [tellurium ion amount]) may be 0.3 to 70%, preferably about 25 to 60%. Thereby, semiconductor nanoparticles in which zinc telluride is mixed in zinc selenide are produced.

Subsequently, the semiconductor nanoparticles of the present invention are obtained by irradiating the semiconductor nanoparticles with ultraviolet light. Also in this case, the emission peak wavelength of the produced semiconductor nanoparticles moves to a longer wavelength than that of the zinc selenide nanoparticles, and is in the range felt by the human eye.
I-3. Group II-VI semiconductors covered with a coating (shell) containing Group II and / or Group VI elements
By irradiating the II-VI group semiconductor nanoparticles obtained in Sections I-1 and I-2 with ultraviolet light in an aqueous solution containing a Group II element and / or a Group VI element and a surfactant. Core-shell type II-VI group semiconductor nanoparticles in which II-VI group semiconductor nanoparticles (core) are covered with a coating (shell) containing a group II element and / or a group VI element can be produced. The group II element or group VI element forming the coating (shell) may be the same as or different from the group II element or group VI element constituting the core II-VI semiconductor nanoparticles. .

  This will be described in detail below by giving examples of nanoparticles in which the surface of zinc selenide nanoparticles is coated with zinc sulfide and cadmium sulfide.

Zinc selenide nanoparticles are used as group II-VI semiconductor nanoparticles before ultraviolet light irradiation. This nanoparticle is precipitated and separated, from the surfactant containing sulfur, thioglycolic acid, zinc ions, and Group II elements having a higher atomic weight than zinc (eg, cadmium) and / or selenium Further, when redispersed in an aqueous solution containing a group VI element having a large atomic weight (for example, tellurium) and irradiating with ultraviolet light, the surface of the semiconductor nanoparticles is covered with a sulfide of the element having a large atomic weight. The semiconductor nanoparticles are covered with an element having an atomic weight larger than that of zinc selenide as a whole, and the emission peak wavelength of the semiconductor nanoparticles moves to a longer wavelength.

For example, in addition to thioglycolic acid and zinc ions, cadmium ions are added to the aqueous solution that is irradiated with ultraviolet light (addition rate of cadmium ([cadmium ion amount] / ([zinc ion amount] + [cadmium ion amount])) When about 0.1 to 10 mol% is added, semiconductor nanoparticles in which the surface of the core semiconductor nanoparticles is coated with a layer made of a mixture of zinc sulfide and cadmium sulfide can be obtained by irradiation with ultraviolet light. . By covering with a layer of such a cadmium compound having a large atomic weight, the emission peak wavelength of the semiconductor nanoparticles moves to a long wavelength. Specifically, Example 6 may be referred to.
I-4. Semiconductor nanoparticles having a coating (shell) containing a group II element and / or a group VI element in a core containing two or more group II elements and / or two or more group VI elements therein Manufacturing semiconductor nanoparticles previously containing two or more Group II elements and / or two or more Group VI elements in an aqueous solution containing Group II elements and / or Group VI elements as a post-treatment step. When irradiated with ultraviolet light, core-shell type II-VI semiconductor nanoparticles are produced.

For example, examples of II-VI group semiconductor nanoparticles having a core mainly containing zinc selenide and additionally containing cadmium selenide or zinc telluride and a coating made of zinc sulfide and cadmium sulfide on the surface thereof will be described below. To do.

  In this case, an element having an atomic weight larger than that of zinc selenide is contained both inside and on the surface of the nanoparticle. As a result of such a synergistic effect, the emission peak wavelength of the semiconductor nanoparticles moves to a longer wavelength than the II-VI group semiconductor nanoparticles obtained in Sections I-2 and I-3.

  For example, in the step of synthesizing the semiconductor nanoparticles described in the above section I-1, using cadmium perchlorate mixed with cadmium perchlorate in addition to zinc perchlorate, cadmium selenide is used. Semiconductor nanoparticles mixed with are produced. This nanoparticle is precipitated and separated, and it is redispersed in an aqueous solution containing a surfactant containing sulfur, thioglycolic acid, zinc ions and cadmium ions, and irradiated with ultraviolet light to selenize in zinc selenide. Semiconductor nanoparticles in which the surfaces of semiconductor nanoparticles (core) mixed with cadmium are coated with a layer made of a mixture of zinc sulfide and cadmium sulfide are obtained.

  For example, semiconductor nanoparticles in which zinc telluride is mixed in zinc selenide are produced using a mixture of hydrogen telluride gas in addition to hydrogen selenide gas as a group VI element compound. When the nanoparticles are precipitated and separated, they are redispersed in an aqueous solution containing a surfactant containing sulfur, thioglycolic acid, zinc ions and cadmium ions, and irradiated with ultraviolet light to tellurize into zinc selenide. Semiconductor nanoparticles in which the surface of semiconductor nanoparticles (core) mixed with zinc is coated with a layer made of a mixture of zinc sulfide and cadmium sulfide are obtained.

  What is necessary is just to make the addition rate of tellurium and the addition rate of cadmium which are added to a core and a shell the same as the said clause I-2 and I-3.

These semiconductor nanoparticles are in a state in which an element having an atomic weight larger than that of zinc selenide as a whole is contained in both the inside and the coating, and the emission peak wavelength of the semiconductor nanoparticles moves to a longer wavelength. Specifically, Examples 7 to 9 may be referred to.
II. Phosphor The phosphor of the present invention is formed by dispersing fluorescent nanoparticles having a light emission peak in a wavelength range of 400 to 500 nanometers and a light emission efficiency of 20% or more (particularly 30% or more) in a glass matrix. This phosphor is obtained by dispersing the semiconductor nanoparticles in a glass matrix by a sol-gel method using organoalkoxysilane.

  The phosphor of the present invention can be produced, for example, as follows.

  A phosphor is produced by adding and mixing an aqueous solution of semiconductor nanoparticles containing a surfactant into a sol solution containing an organoalkoxysilane, followed by hydrolysis and polycondensation.

  As the aqueous solution of the semiconductor nanoparticles containing the surfactant used in the method for producing the phosphor of the present invention, the aqueous solution produced in the above-mentioned section “I. Semiconductor nanoparticles” can be used as it is. Among them, it is preferable to use a solution in which purified nanoparticles are redispersed in an aqueous solution containing a group II ion and a surfactant and subjected to ultraviolet light irradiation treatment.

The concentration of the semiconductor nanoparticles in this aqueous solution is, for example, about 5 × 10 ^{−6 to} 1.5 × 10 ⁻⁴ mol / liter, preferably about 1 × 10 ^{−5 to} 1.2 × 10 ⁻⁴ mol / liter. The concentration of elemental ions is, for example, about 0.04 to 0.3 mol / liter, preferably about 0.06 to 0.15 mol / liter, and the concentration of the surfactant is, for example, II contained in an aqueous solution. About 1.5 to 3.5 mol, preferably about 2.2 to 2.8 mol, per mol of group element ion. The pH of the aqueous solution is usually about 9.5 to 11.5, preferably about 10.5 to 11.4.

The organoalkoxysilane used in the method for producing the phosphor of the present invention is a compound having a skeleton structure containing silicon, in which at least one of the four bonds of silicon has a carbon atom, (I):
SiX _n (OR) _4-n (I)
(Wherein n = 1, 2 or 3, R represents an alkyl group, X represents an aminoalkyl group, a mercaptoalkyl group, a haloalkyl group or a phenyl group)
It is a compound represented by these.

  n is preferably 1 or 2, and n is particularly preferably 1.

  Examples of the alkyl group represented by R include C1-C4 alkyl groups such as methyl, ethyl, n-propyl, isopropyl and n-butyl. Preferred are methyl and ethyl.

The amino alkyl group represented by X, for _{example, NH 2 C m H 2m -} (m is an integer of 1 to 6) include groups represented by, in particular a linear _{H 2 N (CH 2) m} - ( A group represented by m is an integer of 2 to 4 is preferred. m is preferably from 2 to 4, particularly preferably 3.

Examples of the mercaptoalkyl group represented by X include a group represented by HSC _q H _2q- (q is an integer of 1 to 10), and in particular, a linear HS (CH ₂ ) _q- (q is 2 to ₂ ). Group represented by an integer of 4). q is preferably from 2 to 4, particularly preferably 3.

Examples of the haloalkyl group represented by X include a group represented by YC _r H _2r — (wherein r is an integer of 1 to 10, Y is a halogen atom), and in particular, linear Y (CH ₂ ) _r — (q is An integer of 2 to 4, Y is preferably a fluorine atom, a chlorine atom or a bromine atom). q is preferably from 2 to 4, particularly preferably 3. Y is preferably a chlorine atom.

Specifically, 3-aminopropyltrimethoxysilane (APS), mercaptopropyltrimethoxysilane (MPS), chloropropyltrimethoxysilane and the like are preferable examples.

Of the organoalkoxysilanes represented by the general formula (I), trialkoxysilane having an aminoalkyl group as a functional group is preferably used. Of these, trialkoxysilane having a group represented by H ₂ N (CH ₂ ) _m — (m is an integer of 2 to 4) is preferable, and APS is particularly preferable. In this case, the dispersibility of the nanoparticles can be increased because the affinity between the carboxyl group of the surfactant adsorbed on the surface of the semiconductor nanoparticles and the amino group is good.

In these organoalkoxysilanes, a glass network structure ((—O—Si—) _p : p> 1) is formed by a normal sol-gel reaction such as hydrolysis and condensation polymerization of alkoxy groups, while the above general formula ( It is considered that the functional group represented by X in I) forms a bond with the surfactant bonded to the surface of the semiconductor nanoparticle and stabilizes it.

The organoalkoxysilane is used in the form used in the usual sol-gel method, that is, in the form of a sol solution containing the organoalkoxysilane. For example, the above-mentioned organoalkoxysilane; alcohol compounds such as ethanol, methanol, propanol, butanol; and water (for example, molar ratio of about 1: 1 to 60: 1 to 20 respectively), hydrochloric acid, acetic acid, nitric acid Then, a small amount of a catalyst such as ammonia is added to prepare a sol solution. However, when the organoalkoxysilane is an organoalkoxysilane containing an amino group such as APS, the reaction proceeds without adding a catalyst. A glass matrix can be formed by adding the above-mentioned aqueous dispersion of semiconductor nanoparticles to the sol solution and causing hydrolysis and polycondensation reaction at room temperature to about 100 ° C.

  Furthermore, it is also useful to add a water-soluble carbodiimide such as 1-ethyl-3- (3-dimethylaminopropyl) carbodiimide hydrochloride (WSC) to the sol solution. The carbodiimide has a function of dehydrating and condensing an amine and a carboxyl group, and by using this, the surfactant on the surface of the nanoparticles and the glass matrix can be chemically bonded to further improve dispersibility. . The amount of carbodiimide used is preferably about 0.5 to 8 times the number of moles of carboxyl groups in the surfactant added to the aqueous solution in which the purified nanoparticles are re-dispersed in water. About 4 times is more preferable.

Furthermore, in order to improve the dispersibility of the semiconductor nanoparticles, a surfactant may be added to the sol solution so as to have a concentration of about 10 ⁻⁵ to 10 ⁻³ mol / liter. The semiconductor nanoparticles can be immobilized in the glass by adjusting the pH of the sol solution to about 9 to 10 and performing the reaction at about room temperature. As the surfactant, it is preferable to use a surfactant having both a thiol group and a hydrophilic group, such as thioglycerol, thioglycolic acid, and mercaptoethylamine.

The amount of the semiconductor nanoparticle aqueous solution added to the sol solution is such that the concentration of the semiconductor nanoparticles in the glass matrix in the produced phosphor is about 2 × 10 ⁻⁶ to 2 × 10 ⁻⁴ mol / liter, preferably 1 It is preferable to prepare so that it may become about * 10 < ^-5 > -2 * 10 < ^-4 > mol / liter, and if it is this range, the fluorescent substance which shows a high brightness | luminance can be obtained.

Here, the concentration of the semiconductor nanoparticles in the glass matrix is determined by measuring the absorption spectrum (absorbance) as described in Non-Patent Document 2 (Radi et al., Journal of Physical Chemistry, Vol. 97, 11999, 1993). Can be estimated almost accurately. That is, for example, in the case of zinc selenide nanoparticles, the extinction coefficient ε of the semiconductor nanoparticles is approximately 1 × 10 ^{5 as} described in the literature (Shim et al., Journal of Chemical Physics, 111, 6955, 1999). Because it is liter / mole centimeter
If the absorbance A and the thickness L (unit centimeter) are known, the concentration c (unit mol / liter) can be easily obtained by c = A / (L × ε).

In the above solution, for the purpose of increasing the crystallinity of the glass matrix, increasing the dispersibility of the semiconductor nanoparticles, increasing the hardness, and further reducing the deterioration, other alkoxides such as tetra Alkoxysilane (tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane and the like), tetraalkoxytitanium (titanium tetraisopropoxide and the like), trialkoxyaluminum (aluminum isopropoxide and the like) and the like can be added. When adding this alkoxide, the addition amount should just be about 0.05-3 mol with respect to 1 mol of organoalkoxysilane.

  The phosphor of the present invention can be produced by the above method. The phosphor can be used after being molded into an arbitrary shape according to the purpose of use. For example, a sol-like reaction liquid in which semiconductor nanoparticles in a sol-gel method are dispersed can be applied to a substrate or the like by a spin coating method, a dip coating method, or the like to form a phosphor thin film having a thickness of about 100 microns or less. is there. Such a phosphor thin film can be used, for example, for adjusting the color tone by being installed on a mirror or a lens.

The phosphor of the present invention formed by the above-described method basically exhibits the properties of glass as a whole, and has excellent properties such as mechanical properties, heat resistance, and chemical stability. . Furthermore, since the semiconductor ultrafine particles encapsulated in the phosphor are shielded from the external atmosphere, they have excellent light resistance and very good temporal stability.
III. The phosphor obtained by the method more than the use of the phosphor has high brightness and exhibits various colored light by irradiation with light of a single wavelength. A light emitting device as shown below (instead of the conventional phosphor) ( It can be effectively used as a phosphor for lighting devices and display elements.

White illumination light can be obtained by combining semiconductor nanoparticles with an appropriate particle size in accordance with excitation by an illumination device, particularly a mercury lamp with a wavelength of 365 nm or an ultraviolet LED. In addition, it can be used as an illumination as a liquid crystal backlight such as a cold cathode fluorescent lamp, a light source for a liquid crystal projector for presentation using a mercury lamp, and the like.

Display element (display, etc.)
A flat plate coated with a phosphor as a fine pattern is used. Nano-particles that emit light of three colors of RGB, for example, are applied alternately to a large number of dots with a diameter of about 0.1 mm, and the desired display is obtained by irradiating ultraviolet light with intensity modulation according to the information signal . For the excitation light source in this case, it is necessary to select a wavelength in a range where there is no absorption of the matrix. When the wavelength is less than 320 nm, matrix absorption often occurs. Therefore, it is preferable to use a light source having a wavelength of about 320 nm to 600 nm, such as a mercury lamp, LED, or solid laser.

  In particular, when intense excitation light is irradiated, the temperature of the phosphor rises and the deterioration is accelerated. The activation energy for deterioration is about 300 meV. For this reason, in order to make it last longer, it is desirable that the operating temperature is as low as possible. For that purpose, it is preferable to devise the arrangement of the excitation light source and to include a cooling device and a heat dissipation material. Examples of the cooling device include a powerful cooling fan and cooling water, and examples of the heat dissipation material include metals and ceramics.

Other uses Since the phosphor produced according to the present invention is highly transparent and uniform, it can be used, for example, for increasing the conversion efficiency of solar cells. Current solar cells mainly use amorphous silicon or single crystal silicon. At this time, there is no sensitivity in the ultraviolet region, and energy may be lost due to absorption of the resin film used for protection. For this reason, by providing this nanoparticle-dispersed glass thin film in front of the sunlight receiving surface, it is possible to efficiently convert ultraviolet rays into visible light and further increase the conversion efficiency.

  The semiconductor nanoparticles of the present invention emit blue region light with high luminous efficiency and high luminous intensity by excitation light irradiation in an aqueous solution. Moreover, the phosphor formed by holding the semiconductor nanoparticles of the present invention in a glass matrix has high luminous efficiency and is used as an element of an optical device such as a high-luminance display device or illumination device. Moreover, the phosphor of the present invention is excellent in stability over time.

  Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

Example 1
2.61 mmol of zinc perchlorate hexahydrate was dissolved in 200 ml of pure water, and 6.33 mmol of thioglycolic acid as a surfactant was added thereto. At this time, the zinc concentration was 0.013 mol / liter. This aqueous solution was adjusted to pH 6.5 with sodium hydroxide solution. This solution was degassed with argon gas, and then hydrogen selenide gas generated by adding sulfuric acid to aluminum selenide was introduced into this aqueous solution with vigorous stirring. Furthermore, zinc selenide nanoparticles were grown by refluxing near 100 ° C. At this stage, the luminescence was very weak.

  Subsequently, 2-propanol, which is a poor solvent, was added to 4 ml of this solution to precipitate zinc selenide nanoparticles, which were centrifuged to take out the zinc selenide nanoparticles.

Further, thioglycolic acid was added to a 0.065 mol / liter zinc perchlorate solution so that the pH was 0.159 mol / liter, and the pH was adjusted to 11.23. The zinc selenide nanoparticle powder was added to 2 ml of this solution and dispersed and dissolved to obtain an aqueous solution having a zinc selenide nanoparticle concentration of about 1 × 10 ⁻⁵ mol / liter. While stirring, this aqueous solution was irradiated for 35 minutes under the condition of 50 mW / cm ^{2 with} light of 365 nm wavelength using an optical fiber with a B lens attached to a spot UV irradiation device (SP-7, manufactured by USHIO). .

Fluorescence spectra were measured before UV irradiation (0 minutes) and every irradiation time (10 minutes, 20 minutes, 35 minutes). As shown in Fig. 2, almost no light was emitted before UV irradiation (0 minutes). The emission intensity of the nanoparticles increased significantly with the irradiation time (10 minutes, 20 minutes, 35 minutes), and the emission peak wavelength shifted to about 410 nanometers. The luminous efficiency after irradiation was 45%. The temperature at the time of irradiation was 23 ° C. As a result, a dispersed aqueous solution of zinc selenide nanoparticles having a concentration of about 1 × 10 ⁻⁵ mol / liter was obtained.

Furthermore, it became clear that it is more effective to increase the irradiation light intensity of ultraviolet light in order to increase the light emission efficiency. Thus, by optimizing the components of the solution and the conditions of the irradiation light, it is possible to emit light. Semiconductor nanoparticles with a peak wavelength of 400 nanometers or more in the visible region and high luminous efficiency were obtained.

Comparative Example 1
In Example 1, when the zinc selenide nanoparticle-dispersed aqueous solution was irradiated with ultraviolet light for more than 4 hours, precipitation of zinc selenide nanoparticles was observed.

Comparative Example 2
In Example 1, when the zinc selenide nanoparticle-dispersed aqueous solution was irradiated with ultraviolet light while maintaining the pH of 6.5 at the time of preparing the aqueous solution, almost no growth of the size of the zinc selenide nanoparticles occurred, and the emission peak wavelength was 400 nanometers. Was less than a meter.

Test example 1
The emission wavelength of the semiconductor nanoparticles when the pH of the aqueous solution obtained in Example 1 was changed (pH 6.52 to 12.14) and irradiated with ultraviolet light (wavelength 365 nm, intensity 140 mW / cm ² , 30 minutes) The relationship with the emission intensity is shown in FIG. In addition, FIG. 4 shows the relationship between the emission efficiency and emission peak wavelength of the semiconductor nanoparticles when the pH of the aqueous solution is changed and ultraviolet irradiation is performed.

  From these results, when the nanoparticle-dispersed aqueous solution is irradiated with ultraviolet rays in the alkaline region, particularly pH 9.5 to 11.5, both the emission intensity and the emission efficiency of the nanoparticles increase, and the nanoparticles grow and emit light peaks. It has been clarified that the emission wavelength in the visible region increases by moving to the longer wavelength side. This is a significant advantage in view of the fact that the conventional zinc selenide nanoparticles produced by irradiating with ultraviolet light near pH 6 had a luminous efficiency of about 30% at the most (for example, Non-Patent Document 4). Is shown.

Example 2
A glass phosphor was produced using the zinc selenide nanoparticle-dispersed aqueous solution 35 minutes after irradiation with ultraviolet light produced in Example 1.

Aminopropyltrimethoxysilane (APS) was diluted with methanol at a molar ratio of 50 times, pure water was further added, and the mixture was stirred at room temperature for 1 hour to proceed hydrolysis. This solution was further allowed to stand for 12 hours, and 1 ml of the aqueous solution containing zinc selenide nanoparticles dispersed in Example 1 (concentration: about 1 × 10 ⁻⁵ mol / liter) was added to 1 ml of the solution whose viscosity increased. Further, the pH was adjusted to 11 by adding zinc perchlorate and thioglycolic acid to 0.0653 mol / liter and 0.159 mol / liter, respectively. In this state, a glass phosphor emitting blue light was produced by leaving it in a Teflon (registered trademark) petri dish for 2 days. The luminous efficiency was measured to be 22%.

Example 3
By heating at the time of light irradiation of the zinc selenide nanoparticle dispersion aqueous solution, the emission wavelength of the semiconductor nanoparticles could be moved further to the longer wavelength side. That is, in Example 1, the temperature at the time of irradiation was 23 ° C., but when this was raised to 40 ° C. and irradiated with light, the emission wavelength shifted to around 430 nanometers. At this time, the luminous efficiency decreased slightly from 45% to 40%. It is interpreted that the heating promoted the decomposition of thioglycolic acid and accelerated particle growth.

Example 4
In Example 1, cadmium perchlorate was mixed into zinc perchlorate as a cadmium addition rate ([cadmium ion amount] / ([zinc ion amount] + [cadmium ion amount])), Semiconductor nanoparticles in which cadmium selenide was mixed in zinc selenide were prepared. The emission peak wavelength of the produced semiconductor nanoparticles moved to a long wavelength of 450 nanometers after light irradiation (wavelength 365 nanometers, intensity 300 mW / cm ² ). At this time, the luminous efficiency was 47% (FIGS. 5 and 6). Since cadmium selenide has a narrower band gap than zinc selenide, it is considered that the emission peak of nanoparticles moves to the longer wavelength side when mixed together.

In addition, when the addition ratio of cadmium perchlorate is 2 mol% and 5 mol%, the emission peak wavelength and the emission efficiency of the produced semiconductor nanoparticles are 418 nm, 39%, and 425 nm, respectively. It was 49% (FIGS. 5 and 6).

Example 5
In Example 1, 50 mol% of aluminum telluride was mixed in aluminum selenide as tellurium addition rate ([tellurium ion amount] / ([selenium ion amount] + [tellurium ion amount])), and sulfuric acid was added dropwise. Hydrogen telluride gas was mixed in hydrogen selenide gas, and semiconductor nanoparticles in which zinc telluride was mixed in zinc selenide were produced.

The nanoparticles were precipitated and separated, re-dispersed in an aqueous solution containing thioglycolic acid and zinc ions, and irradiated with light. The emission peak wavelength of the semiconductor nanoparticles thus produced shifted to a long wavelength of 456 nanometers after light irradiation (wavelength 365 nanometers, intensity 300 mW / cm ² ) (FIG. 7). At this time, the luminous efficiency was 23%. In this case as well, as in Example 4, zinc telluride has a narrower band gap than zinc selenide. Therefore, it is considered that the emission peak of nanoparticles moves to the longer wavelength side when mixed together.

Further, when the addition ratio of aluminum telluride ([tellurium ion amount] / ([selenium ion amount] + [tellurium ion amount]) is 10 mol% and 30 mol%, the emission peak wavelength of the produced semiconductor nanoparticles The luminous efficiencies were 415 nanometers and 35%, and 430 nanometers and 30%, respectively (Fig. 7).

  Moreover, the zinc selenide nanoparticle dispersion aqueous solution mixed with aluminum telluride was heated and irradiated with light in the same manner as in Example 3 to move the emission wavelength of the semiconductor nanoparticles further to the longer wavelength side. .

When the addition rate of aluminum telluride ([tellurium ion content] / ([[selenium ion content] + [tellurium ion content])) is 30 mol%, the emission peak wavelength and luminous efficiency of the produced semiconductor nanoparticles are When the temperature was raised to 80 ° C. and irradiated with light, the emission wavelength shifted to around 450 nanometers. At this time, the luminous efficiency was 29%.

  As described above, nanoparticles composed of a mixture of zinc selenide and zinc telluride are particularly excellent in heat resistance, and their luminous efficiency hardly changed even when irradiated with light at a high temperature. In addition, nanoparticles composed of a mixture of zinc selenide and zinc telluride have almost the same emission wavelength and luminous efficiency when heated to room temperature to 80 ° C after light irradiation and then returned to room temperature again after heating. It didn't change.

Example 6
Zinc selenide nanoparticles synthesized without adding cadmium were precipitated and separated, and then redispersed in an aqueous solution containing thioglycolic acid, zinc ions, and cadmium ions, and irradiated with light. That is, irradiation with ultraviolet light of a zinc selenide nanoparticle dispersion aqueous solution was added with 2.5 mol% of cadmium ions as cadmium addition rate ([cadmium ion amount] / ([zinc ion amount] + [cadmium ion amount])). When performed in an aqueous solution, the emission wavelength is light irradiation (wavelength 365).
After nanometer, intensity 300mW / cm ² ), it moved to 449 nanometer. At this time, the luminous efficiency was 39% (FIGS. 8 and 9).

  Since the zinc sulfide shell containing cadmium sulfide coats the surface of the zinc selenide nanoparticle core, the band gap of the nanoparticle is narrowed, and the emission wavelength is interpreted as a long wavelength shift.

  The addition rate of cadmium ions is 0.7 mol%, 1.1 mol%, and 1.7 as the addition rate of cadmium ([cadmium ion amount] / ([zinc ion amount] + [cadmium ion amount])). In the case of mol%, the emission peak wavelength and emission efficiency of the prepared semiconductor nanoparticles were 425 nanometers and 34%, 436 nanometers and 38%, 446 nanometers and 41%, respectively (FIG. 8). 9).

Example 7
Nanoparticles composed of zinc selenide and cadmium selenide were precipitated and separated, re-dispersed in an aqueous solution containing thioglycolic acid, zinc ions and cadmium ions, and irradiated with light. That is, cadmium ions are added at the time of synthesis as cadmium addition rate ([cadmium ion amount] / ([zinc ion amount] + [cadmium ion amount])), and consists of zinc selenide and cadmium selenide. Prepare a nanoparticle-dispersed aqueous solution and add 2 mol% of cadmium ions to the aqueous solution as cadmium addition rate ([cadmium ion amount] / ([zinc ion amount] + [cadmium ion amount])). Went. The emission wavelength moved to 472 nm after light irradiation (wavelength 365 nm, intensity 300 mW / cm ² ). At this time,
The luminous efficiency was 40% (FIGS. 10 and 11).

  In addition to the inclusion of cadmium inside the nanoparticles, the outer surface of the nanoparticles is covered with a zinc sulfide shell containing cadmium sulfide, which further reduces the band gap of the nanoparticles, resulting in an emission wavelength. Is interpreted as a long wavelength shift.

Further, the mixing ratio of cadmium ions at the time of light irradiation is 0.5 mol% and 0.7 mol% as cadmium addition rate ([cadmium ion amount] / ([zinc ion amount] + [cadmium ion amount])). And 1 mol%, the emission peak wavelength and emission efficiency of the prepared semiconductor nanoparticles were 452 nm and 44%, 459 nm and 46%, 467 nm and 43%, respectively ( 10 and 11).

Example 8
In Example 7, the cadmium ions were converted into cadmium ions at the time of light irradiation of the nanoparticles composed of zinc selenide and cadmium selenide ([cadmium ion amount] / ([zinc ion amount] + [cadmium ion amount])). Add 0.5 mol% to make nanoparticles. A glass phosphor was produced in the same manner as in Example 2 using a dispersed aqueous solution of these nanoparticles (emission peak wavelength: 452 nm, emission efficiency: 44%).

  As a result, a glass phosphor emitting blue light in a Teflon (registered trademark) petri dish was produced. The emission peak wavelength of this glass was 451 nanometers, and the emission efficiency was 31%. FIG. 12 shows emission spectra of the nanoparticle-dispersed aqueous solution and the nanoparticle-dispersed glass.

Example 9
A nanoparticle-dispersed aqueous solution composed of zinc selenide and cadmium selenide was precipitated and separated, then re-dispersed in an aqueous solution containing thioglycolic acid, zinc ions, and cadmium ions, and irradiated with light. In other words, the nanoparticle composed of zinc selenide and cadmium selenide, in which 10 mol% of cadmium ion was added at the time of synthesis as cadmium addition rate ([cadmium ion amount] / ([zinc ion amount] + [cadmium ion amount])). Irradiation of the particle-dispersed aqueous solution with ultraviolet light was performed in an aqueous solution in which cadmium ions were added at 2 mol% as the cadmium addition rate ([cadmium ion amount] / ([zinc ion amount] + [cadmium ion amount])).

As a result, the emission wavelength moved to 483 nanometers after light irradiation (wavelength 365 nanometers, intensity 300 mW / cm ² ). At this time, the luminous efficiency was 44% (FIGS. 13 and 14). As in Example 7, since cadmium is contained in the inside and outside surfaces of the nanoparticle, the band gap of the nanoparticle is further narrowed, and the emission wavelength is interpreted as a long wavelength shift.

  Moreover, the addition rate of cadmium ions at the time of light irradiation is 0.5 mol% and 0.7 mol% as an addition rate of cadmium ([cadmium ion amount] / ([zinc ion amount] + [cadmium ion amount])). And 1 mol%, the emission peak wavelength and emission efficiency of the prepared semiconductor nanoparticles were 472 nanometers and 37%, 475 nanometers and 42%, 479 nanometers and 48%, respectively ( (FIGS. 13 and 14).

It is a figure which shows the relationship between the kind of II-VI group semiconductor (bulk body), and band gap energy. Changes in emission intensity and emission peak wavelength of zinc selenide nanoparticles at each irradiation time (0 min, 10 min, 20 min, 35 min) when an aqueous solution of zinc selenide nanoparticles was irradiated with 365 nanometer light It is a graph which shows. It is a graph which shows the change of the emitted light intensity and emission peak wavelength of the zinc selenide nanoparticle aqueous solution in the pH of each aqueous solution when light irradiation (140 mW / cm < ² >, 30 minutes) is carried out to the aqueous solution of a zinc selenide nanoparticle. It is a graph which shows the change of the luminous efficiency and emission peak wavelength of zinc selenide nanoparticle aqueous solution in pH of each aqueous solution when light irradiation (140 mW / cm < ² >, 30 minutes) is carried out to the aqueous solution of zinc selenide nanoparticle. In Example 4, it is a graph which shows the relationship between the addition amount of the cadmium ion at the time of nanoparticle synthesis | combination, and the light emission peak wavelength of the produced semiconductor nanoparticle. It is a graph which shows the relationship between the luminous efficiency of FIG. 5, and the light emission peak wavelength. In Example 5, it is a graph which shows the relationship between the addition rate of the tellurium ion at the time of nanoparticle synthesis | combination, and the light emission peak wavelength of the produced semiconductor nanoparticle. In Example 6, it is a graph which shows the relationship between the addition rate of the cadmium ion in the aqueous solution at the time of light irradiation, and the emission peak wavelength of the produced semiconductor nanoparticle. It is a graph which shows the relationship between the luminous efficiency of FIG. 8, and the light emission peak wavelength. In Example 7, it is a graph which shows the relationship between the addition rate of the cadmium ion in the aqueous solution at the time of light irradiation, and the emission peak wavelength of the produced semiconductor nanoparticle. It is a graph which shows the relationship between the luminous efficiency of FIG. 10, and the light emission peak wavelength. It is a graph which shows the emission spectrum of the nanoparticle dispersion | distribution aqueous solution and nanoparticle dispersion | distribution glass which were produced in Example 8. FIG. In Example 9, it is a graph which shows the relationship between the addition rate of the cadmium ion in the aqueous solution at the time of light irradiation, and the emission peak wavelength of the produced semiconductor nanoparticle. It is a graph which shows the relationship between the luminous efficiency of FIG. 13, and the light emission peak wavelength.

Claims (23)

  Semiconductor nanoparticles having an emission peak in the wavelength range of 400 to 500 nanometers and an emission efficiency of 35% or more when dispersed in water.   The semiconductor nanoparticle according to claim 1, wherein the emission efficiency in a state dispersed in water is 45% or more. The semiconductor nanoparticle according to claim 1 or 2, wherein the semiconductor nanoparticle is a II-VI group semiconductor nanoparticle. The semiconductor nanoparticles are II-VI group semiconductor nanoparticles containing at least one selected from the group consisting of cadmium sulfide, zinc selenide, cadmium selenide and zinc telluride.
Semiconductor nanoparticles described in 1.   The semiconductor nanoparticle according to claim 3, wherein the semiconductor nanoparticle is zinc selenide. The semiconductor nanoparticle according to claim 3, wherein the semiconductor nanoparticle is a II-VI group semiconductor nanoparticle comprising two or more selected from the group consisting of cadmium sulfide, zinc selenide, cadmium selenide and zinc telluride. The semiconductor nanoparticles according to claim 3, wherein the semiconductor nanoparticles are II-VI group semiconductor nanoparticles containing two or more group II elements and / or two or more group VI elements.   In addition to zinc selenide, the semiconductor nanoparticles include a group II-VI semiconductor containing at least one selected from the group consisting of a group II element having a larger atomic weight than zinc and a group VI element having a larger atomic weight than selenium. The semiconductor nanoparticle according to claim 3, which is a nanoparticle.   The semiconductor nanoparticle according to claim 3, wherein the semiconductor nanoparticle contains cadmium and / or tellurium in addition to zinc selenide. A method for producing II-VI group semiconductor nanoparticles according to claim 3, wherein (1) a water-soluble compound containing a group II element and a surfactant are dissolved in an aqueous solution having a pH of about 6-7. In an active atmosphere, a group VI element compound was introduced to prepare a dispersed aqueous solution of group II-VI semiconductor nanoparticles.
2) Thereafter, the dispersion aqueous solution of the II-VI group semiconductor nanoparticles is adjusted to pH 9.5 to 11.5 and irradiated with ultraviolet light.   The manufacturing method according to claim 10, wherein the water-soluble compound containing a group II element in (1) is a mixture of two or more water-soluble compounds having different group II elements.   The production method according to claim 10 or 11, wherein the group VI element compound in (1) is a mixture of two or more group VI element compounds having different group VI elements. The production according to any one of claims 10 to 12, wherein a group II element and / or a group VI element are further added to the aqueous dispersion of the group II-VI semiconductor nanoparticles in (2), followed by ultraviolet irradiation. Method. In the above (1), the II group element of the water-soluble compound containing the II group element is zinc, and the VI group element of the VI group element compound is selenium. In the above (2), the II-VI group semiconductor (selenated) Claims: At least one selected from the group consisting of a group II element having a larger atomic weight than zinc and a group VI element having a larger atomic weight than selenium is added to an aqueous solution of zinc) nanoparticles, and then irradiated with ultraviolet light. 10. The production method according to 10.   The production method according to claim 14, wherein the Group II element having an atomic weight larger than that of zinc is cadmium.   The production method according to claim 14, wherein the VI group element having an atomic weight larger than that of selenium is tellurium.   A phosphor in which semiconductor nanoparticles with a light emission peak in the wavelength range of 400 to 500 nanometers and a light emission efficiency of 20% or more are dispersed in a glass matrix.   The phosphor according to claim 17, wherein semiconductor nanoparticles having a luminous efficiency of 30% or more are dispersed.   The phosphor according to claim 17 or 18, wherein the phosphor is produced using an organoalkoxysilane. The phosphor according to claim 17, 18 or 19, wherein the semiconductor nanoparticles are II-VI group semiconductor nanoparticles. The semiconductor nanoparticles are II-VI group semiconductor nanoparticles containing at least one selected from the group consisting of cadmium sulfide, zinc selenide, cadmium selenide and zinc telluride.
The phosphor according to 7, 18 or 19. The phosphor according to claim 17, 18 or 19, wherein the semiconductor nanoparticles are II-VI group semiconductor nanoparticles containing two or more group II elements and / or two or more group VI elements.   The method for producing a phosphor according to claim 17, wherein the semiconductor nanoparticles according to any one of claims 1 to 9 are dispersed in a glass matrix by a sol-gel method using an organoalkoxysilane. Production method.

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