JP5506215B2 - Method for manufacturing phosphor - Google Patents

Description

The present invention relates to a method for manufacturing a phosphor, and more specifically, an ultraviolet-excited blue-green phosphor, FED (electrolytic emission display), inorganic EL, or the like that emits high-luminance fluorescence in the emission wavelength region of a near-ultraviolet light-emitting diode. The present invention relates to a method for producing a rare earth element-added rare earth element-added barium thiosilicate (Ba ₂ SiS ₄ ) phosphor that can be suitably used as a blue-green phosphor used in a display.

In recent years, the development of white LEDs has progressed, and it is expected as illumination replacing incandescent lamps and fluorescent lamps.
A conventional white LED is obtained by dispersing a phosphor in which Ce is added to a YAG-based oxide known from the composition formula of (Y, Gd) ₃ (Al, Ga) ₅ O ₁₂ in a blue LED sealing resin. (See Patent Documents 1 to 3). Although these are used for the front light of a mobile phone or a simple lighting device, these white LEDs have poor color reproducibility and color rendering, and their improvement has been demanded.

On the other hand, blue excitation white LED (refer patent document 4) which combined blue LED, green fluorescent substance, and red fluorescent substance (refer patent document 4), ultraviolet excitation white LED which combined ultraviolet light emitting LED, blue fluorescent substance, green fluorescent substance, and red fluorescent substance (See Patent Document 5) has been developed.
In particular, since the UV-excited white LED uses a blue phosphor, the wavelength of the three colors is adjusted so that color reproducibility is good and the UV-excited phosphor that absorbs less visible light is used so that the phosphor does not emit light. Indicates white. In view of the application to fluorescent lamps, it is a great advantage that the phosphor is white.

As such a phosphor for ultraviolet-excited white LED, for example, BaMgAl ₁₀ O ₁₇ : Eu ²⁺ (BAM) or (Mg, Ca, Sr, Ba) ₁₀ (PO ₄ ) ₅ Cl ₂ : Eu ²⁺ is used as a blue phosphor. Etc. are known. However, it has been pointed out that these phosphors have insufficient light conversion efficiency under near-ultraviolet excitation, and Ba ₂ SiS ₄ : Ce ³⁺ blue phosphors have been developed (see Patent Document 6).

By the way, the high color rendering fluorescent lamp does not simply emit light of three colors of blue, green and red, but emits blue-green light having a wavelength of 480 to 500 nm. (Ba, Ca, Mg) ₁₀ (PO ₄ ) ₆ Cl ₂ : Eu ²⁺ (peak wavelength 483 nm) and Sr ₄ Al ₁₄ O ₂₅ : Eu ²⁺ (peak wavelength 493 nm) are known as such phosphors. .

Further, as the ultraviolet LED excitation blue-green phosphor JEM _{phosphor, Ce x Ca y La 1-} x-y Al (Si 5 Al) N 9 O ( refer to Patent Document 7) are known.
Such ultraviolet LEDs are known to have high emission efficiency at an emission wavelength of 390 to 405 nm, but these phosphors have poor emission efficiency at an excitation wavelength of 390 to 405 nm (Non-Patent Documents 1 and 2). reference). On the other hand, Ba ₂ SiS ₄ : Eu ²⁺ has recently been reported as a blue-green phosphor with high emission efficiency at an emission wavelength of 390 to 405 nm (see Non-Patent Document 3).

Japanese Patent No. 2900928 Japanese Patent No. 2927279 Japanese Patent No. 2998696 JP 2000-244021 A JP 2000-509912 A JP 2006-265501 A JP 2006-232868 A

Chapter 2 of Fluorescent Substances Association “Phosphor Handbook” Chapter 2 Nakanishi, Hata Koshi ed. "Physics and application of light emission and light reception" Baifukan Chapter 5.3 Taikan, Ohashi: Proceedings of the 321st phosphor society

However, in order to produce sulfides such as barium sulfide and europium sulfide, which are the raw materials for phosphors, it is usually necessary to use toxic and odor-prone hydrogen sulfide gas to perform the sulfurization reaction. Ensuring safety is a major issue.
In addition, Si sulfides are difficult to synthesize and cannot be easily obtained, and are highly hygroscopic and unstable. Weighing and mixing should be done using a glove box so that it does not decompose during firing. Therefore, in the synthesis of phosphor Ba ₂ SiS ₄ , it is conceivable to use metal Si as the Si source. Ba ₂ SiS ₄ is synthesized by mixing and baking this metal Si and sulfide, but toxic hydrogen sulfide is required as in the case of producing sulfides such as barium sulfide and europium sulfide as a sulfide source. On the other hand, this hydrogen sulfide is not only toxic, but also a malodorous substance and an unstable substance. Therefore, even in a trace amount, strict management is required, which leads to a decrease in manufacturing cost and production efficiency. Problems arise. Further, it is difficult to synthesize Ba ₂ SiS ₄ to which Eu is uniformly added by these methods.

The present invention has been made in view of the present situation, and a rare earth-added Ba ₂ SiO ₄ or a rare earth-added Ba ₂ SiO ₄ and a rare earth-added BaCO ₃ , and a mixture of a rare earth-added Ba (NO ₃ ) ₂ and SiO ₂ , Method for producing rare earth element-added barium thiosilicate phosphor, which safely and efficiently produces rare earth-added Ba ₂ SiS ₄ phosphor with high fluorescence brightness by heat treatment in an inert gas containing carbon disulfide and reducing sulfide Is to provide.

The phosphor manufacturing method according to the present invention includes: 1) Ba ₂ SiO ₄ in which Eu element is uniformly dispersed (Claim 1) , or 2) Ba ₂ SiO ₄ in which Eu element is uniformly dispersed, Eu rare earth element A first step of synthesizing a mixture ( Ba claim 2) comprising Ba (NO ₃ ) ₂ and SiO ₂ in which uniformly dispersed BaCO ₃ and Eu elements are uniformly dispersed, and Eu obtained in this first step _Ba 2 SiO ₄ elements are uniformly dispersed, or, _Ba 2 _SiO 4, BaCO the Eu element is uniformly dispersed _3, Eu elements are uniformly dispersed Ba _{(NO 3)} the Eu elements are uniformly dispersed ₂ and SiO a mixture of _2, then heat treated in an inert gas containing carbon disulfide, in the manufacturing method of the Eu-doped barium thiosulfate silicate phosphor, characterized in that comprising a second step of reducing sulfide, JP In which good phosphor performance is obtained when using the Eu rare earth element.

In the first step in the production method of the present invention, water-soluble silicon or fumed SiO ₂ , Ba nitrate and europium acetate are dissolved in water, stirred for 30 minutes, and then dried by a method such as spray drying or freeze drying. The dried product is fired at a temperature of 700 to 900 ° C., so that 1) a rare earth element-added Ba ₂ SiO ₄ in which rare earth elements are uniformly dispersed, or 2) Ba ₂ SiO ₄ in which rare earth elements are uniformly dispersed. , Characterized in that it is a mixture composed of BaCO ₃ in which rare earth elements are uniformly dispersed, Ba (NO ₃ ) ₂ and SiO ₂ in which rare earth elements are uniformly dispersed, and the second step is obtained in the first step. , 1) Eu added _Ba 2 SiO ₄ with a rare earth element is uniformly dispersed, or, 2) _Ba 2 SiO ₄ with a rare earth element is uniformly dispersed, the rare earth element is uniformly dispersed BaCO _3, Ba _{(NO 3)} a rare earth element is uniformly dispersed ₂ and mixture consisting SiO _2, the heat treatment temperature of 900-1090 ° C. in an inert gas flow under containing carbon disulfide, reducing sulfide A Ba ₂ SiS ₄ phosphor is produced.

The present invention is a method for producing a rare earth element-added Ba ₂ SiS ₄ phosphor, and particularly when Eu is used as the rare earth element, Eu addition Ba ₂ SiO ₄ in which Eu is uniformly dispersed, or Eu is uniformly dispersed. First step of synthesizing a mixture of BaCO ₃ , Ba (NO ₃ ) ₂ and SiO ₂ in which Ba ₂ SiO ₄ and Eu are uniformly dispersed, and Eu (N ₃ ) ₂ and SiO ₂ in which Eu is uniformly dispersed, and Eu obtained in the first step Of Eu-added Ba ₂ SiO ₄ in which Eu is uniformly dispersed, Ba ₂ SiO ₄ in which Eu is uniformly dispersed, BaCO ₃ in which Eu is uniformly dispersed, Ba (NO ₃ ) ₂ and SiO ₂ in which Eu is uniformly dispersed A phosphor manufacturing method comprising a second step in which a mixture is reduced and sulfided by heat treatment in an inert gas containing carbon disulfide. As a raw material, metal Si, barium sulfide, europium sulfide, etc. Thus, high-quality crystals can be obtained without using any sulfide, and a high-luminance Eu-added Ba ₂ SiS ₄ phosphor can be produced without using toxic hydrogen sulfide.

The Ar gas in Embodiment 1 of the present invention is a diagram showing a method to include carbon disulfide (CS _2). It is a figure which shows the X-ray-diffraction measurement result of the dried material after the spray-drying of Example 1, the baked material which baked it at 800 degreeC, and the sulfide powder after reductive sulfidation by the method of this invention. It is a figure which shows the X-ray-diffraction measurement result of the baked product baked at 800 degreeC of Example 3 of this invention, and the sulfide powder produced in Example 3 and Example 4. FIG. It is a figure which shows the powder X-ray-diffraction measurement result after the reductive sulfidation in Examples 5-8 of this invention. Shows the fluorescence spectrum of Eu added _Ba 2 SiS ₄ phosphor in Example 1 of the present invention.

1. First step of synthesizing Eu-added Ba ₂ SiO _{4 in} which Eu of a rare earth element is uniformly dispersed:
First, in order to synthesize Eu-added Ba ₂ SiO ₄ , it is preferable to use water-soluble silicon or fumed SiO ₂ as the Si source to be added.
Water-soluble silicon is produced by the following method. Tetraethoxysilane (TEOS) and propylene glycol are weighed in the same amount as raw materials, mixed at 80 ° C. for 48 hours, a small amount of hydrochloric acid (about 0.2% of the mixed solution) is added to this mixed solution, and the mixture is stirred for 1 hour. Distilled water is added to the stirring liquid to produce water-soluble silicon having a concentration of 1M. The fumed SiO ₂ as the Si source preferably has a particle size of about 5 to 10 nm.

Next, the Si source, Ba nitrate and europium acetate are dissolved in water so that the molar ratio of Si of the Si source to (Ba + Eu) is 1: 2. The solution is stirred at room temperature to prepare an aqueous solution containing the precursor. Here, when spray drying is used for drying the aqueous solution, an aqueous solution of 0.02 to 0.4 mol / L is preferable, and when lyophilization is used, an aqueous solution of 0.2 to 0.4 mol / L is preferable.
In addition, as a Ba source to be added, a water-soluble Ba salt such as Ba nitrate or Ba acetate, and a water-soluble Eu salt as a europium source can be used.

Next, this aqueous solution is dried to obtain a dried product, and the oxide precursor in the first step is prepared.
The aqueous solution is dried using a spray drying method or a freeze drying method. First, when drying using a spray dryer, the aqueous solution is stirred for 20 to 40 minutes, and the solution is sent to the spray dryer by a pump and dried. The drying conditions are preferably a dryer inlet temperature of 200 ° C. and a pressurized air pressure of 0.1 MPa.

  When lyophilization is performed, the aqueous solution is stirred for 10 minutes to prepare a gel containing Eu uniformly. The gel is frozen with a lyophilizer at −30 ° C. for 1 hour and then with a vacuum pump. Exhaust to 0.00603 atmospheres or less. Thereafter, the film is dried at -25 ° C, 3 hours, -20 ° C, 5 hours, -15 ° C, 8 hours, 30 ° C, 5 hours.

Subsequently, Eu-added Ba ₂ in which Eu is uniformly dispersed by subjecting the oxide precursor of the dried product to a temperature of 70 to 1100 ° C., more preferably 750 to 1000 ° C., for 1 to 3 hours. SiO ₄ is produced. From the analysis of TG-DTA of the oxide precursor, desorption of water starts from 200 ° C., residual organic substances are desorbed at 400 ° C. or higher, nitric acid is desorbed at 600 ° C., and the weight becomes constant at 700 ° C. or higher. Therefore, an oxide can be synthesized by firing at a temperature of 700 ° C. or higher.

From the XRD of the dried product after spray drying when water-soluble silicon is used, there is only a peak of Ba nitrate, but when the dried product is baked at 800 ° C., a diffraction pattern of Ba ₂ SiO ₄ is obtained. Further, when the dried product after spray drying when fumed SiO ₂ is used is baked at 800 ° C., a diffraction pattern of a mixture of Ba ₂ SiO ₄ and carbonic acid Ba is obtained.
The upper limit of the firing temperature is 1100 ° C. or less, but if it exceeds 1000 ° C., CS ₂ reductive sulfidation in the second step becomes difficult, so 1000 ° C. or less is more preferable.

In the first step, Eu nitrate was dissolved in water, oxycarboxylic acid, glycol or water, barium carbonate, fumed SiO ₂ were sequentially added, and further heated to 120 to 250 ° C. to obtain a gel. Later, this gel was heat-treated at 400 to 500 ° C. to prepare a carbonate precursor, and the obtained carbonate precursor was heat-treated at 700 to 1090 ° C. to obtain Eu-added Ba ₂ SiO ₄ in which Eu was uniformly dispersed. It is also possible to produce it.
Also, barium carbonate, Eu ₂ O ₃ powder and SiO ₂ powder are mixed and fired in the air or in a reducing atmosphere at 700 to 1000 ° C., whereby Eu added Ba ₂ SiO ₄ , or Eu added BaCO ₃ and SiO ₂ powder. It is also possible to produce a mixed powder.

2. Second step of producing Eu-added Ba ₂ SiS ₄ phosphor by heat-treating Eu-added Ba ₂ SiO ₄ in an inert gas containing carbon disulfide and reducing and sulfidizing the same:
In this second step, the Eu-added Ba ₂ SiO ₄ powder obtained in the first step is heated in an inert gas containing carbon disulfide (CS ₂ ) at 900 to 1090 ° C. for 2 to 8 hours. Heat treatment is performed to obtain a fired product of Eu-added Ba ₂ SiS ₄ phosphor powder.

The temperature of this heat treatment is preferably 900 to 1090 ° C., and if it is less than 900 ° C., reductive sulfidation is insufficient, which is not preferable, and if it exceeds 1090 ° C., which is the melting point of silicon sulfide, partial melting occurs. There is a possibility that the fired product becomes non-uniform due to the movement of the melted liquid, which is not preferable. In general, it is said that sulfur vapor pressure becomes high at high temperatures, and sulfur is volatilized from the sulfide surface.
As the container used for the synthesis, an oxide such as graphite, zirconia, or alumina, or a heat-resistant container such as BN can be used, but graphite and zirconia are preferable because alumina is reduced at a high temperature and impurities are increased.

As the inert gas used here, an inert gas such as Ar gas is preferable, and as a method of including carbon disulfide (CS ₂ ) in the inert gas, an inert gas as shown in FIG. A method of passing through carbon disulfide can be used. The temperature of carbon disulfide and inert gas is 15 ° C. or higher and lower than 46 ° C., especially 20 ° C. to 25 ° C. Undesirably, a temperature of 46 ° C. or higher is not preferable because it becomes higher than the boiling point of carbon disulfide, making it difficult to control the amount of evaporation and making uniform reduction sulfurization difficult. In addition to Ar gas, nitrogen can be used as the inert gas. However, using nitrogen at a high temperature is not preferable because nitride may be formed.

Identification of the fired product of the obtained powder was performed using X-ray diffraction.
A Ba ₂ SiS ₄ single phase was obtained from the oxide obtained by spray drying using water-soluble silicon as a raw material and reduced and sulfided at 1010 ° C. When the baked product of the first step contains carbonate or when the reduced sulfidation temperature is low, an X-ray diffraction pattern including a small amount of a different phase that seems to be BaS was observed. it was found _{that Ba} 2 SiS ₄ single phase is obtained by a 1090 ° C..

First step: Synthesis of Eu-added Ba ₂ SiO ₄ [Preparation of oxide precursor in first step]
Water-soluble silicon was produced as follows. Tetraethoxysilane: 22.4 ml of TEOS (manufactured by Kanto Chemical Co., Ltd.) and propylene glycol (99% manufactured by Kanto Chemical Co., Ltd.) were weighed and mixed at 80 ° C. for 48 hours. Further, 100 μl of hydrochloric acid was added to the mixed solution and stirred at room temperature for 1 hour. Distilled water was added to this stirring solution and dissolved in 100 ml to prepare 1M water-soluble silicon.

  15 mmol of this water-soluble silicon, 28.5 mmol of Ba nitrate and 1.5 mmol of europium acetate (manufactured by Furuuchi Chemical Co., Ltd.) were added to pure water and dissolved in 500 ml, and this aqueous solution was stirred at room temperature for 30 minutes.

Next, the aqueous solution was put into a spray dryer (ADL310 manufactured by YAMATO) and spray-dried to prepare a dried product. The drying conditions were an inlet temperature of 200 ° C., an air volume of 0.55 cubic meters / min, a pump speed of 5 ml / min, and a pressurized air pressure of 0.1 MPa.
The dried product was immediately put in an alumina container, preheated at 100 ° C. to remove moisture in a box furnace, and calcined at 800 ° C. for 2 hours.

[Reduction sulfidation in the second step]
Thereafter, the fired product is put into an alumina boat and heat treated at 1010 ° C. for 2 hours under an Ar flow through a liquid carbon disulfide (99% manufactured by Wako) by the method shown in FIG. Added Ba ₂ SiS ₄ was produced. The Ar flow rate was 50 ml / min, and the flow rate was controlled with a digital flow meter (Model 8300 manufactured by Kofloc).

The measurement results of the X-ray diffraction patterns of the dried product after spray drying, the calcined product calcined at 800 ° C., and the sulfide after reduced sulfidation are shown in FIGS. 2 (a), (b) and (c). From FIG. 2 (a), the dried product is Ba nitrate, from (b) the calcined product calcined at 800 ° C. is Ba ₂ SiO ₄ and from (c), Ba ₂ SiS ₄ was synthesized by reductive sulfidation. I understand that.

In the same manner as in Example 1, only the heat treatment time for the reduction sulfidation in the second step was changed from 2 hours to 4 hours, and the Eu-added Ba ₂ SiS ₄ phosphor was produced under the same conditions.

In the same manner as in Example 1, water-soluble silicon was changed to fumed SiO ₂ (manufactured by Sigma Aldrich, particle size: 7 nm) as the Si source, and Ba nitrate was changed to Ba acetate (99%, manufactured by Wako) as the Ba source. Produced an Eu-added Ba ₂ SiS ₄ phosphor by the same method.

An Eu-added Ba ₂ SiS ₄ phosphor was produced in the same manner as in Example 3 except that the reduced sulfurization temperature (heat treatment temperature) 1010 ° C. in the second step was changed to 950 ° C.

Here, the measurement result of the X-ray-diffraction pattern of the baked product baked at 800 ° C. in Example 3 and the sulfide produced in Examples 3 and 4 is shown in FIG.
From FIG. 3 (a), the fired product fired at 800 ° C. in Example 3 is a mixture of Ba ₂ SiO ₄ and BaCO _{3. From} FIGS. 3 (b) and 3 (c), when reduced and sulfurized at 950 ° C., Ba It can be seen that a mixture of ₂ SiS ₄ and BaS is synthesized.

10 mmol of water-soluble silicon prepared in Example 1, 20 mmol of barium acetate and 1 mmol of europium acetate were dissolved in 30 ml of pure water, and this aqueous solution was stirred at room temperature for 10 minutes to prepare a gel containing Eu uniformly.
Next, this gel is frozen at −30 ° C. for 1 hour with a freeze dryer and evacuated with a vacuum pump to 0.00603 atmospheres or less. Thereafter, it was dried by changing the conditions such as -25 ° C, 3 hours, -20 ° C, 5 hours, -15 ° C, 8 hours, 30 ° C, 5 hours.

Immediately after drying, the dried product was put in an alumina container, preheated at 100 ° C. to remove moisture in a box furnace, and fired at 800 ° C. for 2 hours.
Thereafter, the fired product was placed in an alumina boat in the same manner as in Example 1 and heat treated at 1010 ° C. for 2 hours under an Ar flow through a liquid carbon disulfide (99% manufactured by Wako) as shown in FIG. Then, reduction sulfurization was performed to produce Eu-added Ba ₂ SiS ₄ . The Ar flow rate was 50 ml / min, and the flow rate was controlled with a digital flow meter (Model 8300 manufactured by Kofloc).

  A sulfide was produced in the same manner as in Example 5 except that the firing temperature in the first step was 1000 ° C.

A sulfide was produced in the same manner as in Example 5 except that the reduced sulfurization temperature in the second step was 1050 ° C.

  A sulfide was produced in the same manner as in Example 5 except that the firing temperature in the first step was 1000 ° C. and the reduced sulfurization temperature in the second step was 1050 ° C.

The measurement results of the X-ray diffraction patterns of the sulfides produced in Examples 5, 6, 7, and 8 are shown in FIG.
4A shows the results of Example 5, FIG. 4B shows the results of Example 6, FIG. 4C shows the results of Example 7, and FIG.
4A, 4C, and 4D show that only the Ba ₂ SiS ₄ phase is formed. On the other hand, FIG. 4B showing Example 6 shows that it is a mixture of Ba ₂ SiS ₄ and BaS.

Next, the fluorescence of these sulfides was measured, and the measurement result of the sulfide of Example 1 is shown in FIG. 5 as a representative.
In FIG. 5, the left spectrum is an excitation spectrum measured by changing the wavelength of the excitation light with an emission wavelength of 500 nm, and the right side is an emission spectrum when the excitation wavelength is 340 nm. The excitation peak is 340 nm, but a sub-peak is also observed at 400 nm, so that there is little decrease in intensity even at an excitation wavelength of around 400 nm.

[Evaluation of brightness]
In order to compare the luminance, the fluorescence measurement results of Examples 1 to 4, Example 7, and Example 8 were compared with the blue phosphor BaMgAl ₁₀ O ₁₇ : Eu (BAM phosphor: manufactured by Kasei Opto).
The BAM phosphor was excited by excitation light having wavelengths of 340 nm and 420 nm, and the fluorescence intensity at an emission wavelength of 450 nm was measured. Similarly, the Eu-added Ba ₂ SiS ₄ phosphor was also excited with excitation light at 340 nm and 420 nm, and the fluorescence intensity at 500 nm in the fluorescence spectrum was obtained. A value obtained by dividing the obtained intensity by the intensity of the BAM phosphor was compared as an intensity ratio. The results are shown in Table 1.

As is clear from Table 1, a high-intensity rare earth-added barium thiosilicate (Ba ₂ SiS ₄ ) phosphor can be produced without using hydrogen sulfide, and 13% to 64% of the integrated intensity of BAM in excitation light having a wavelength of 340 nm. It can be seen that excitation light with a wavelength of 420 nm has a sufficient intensity with an intensity of 63% to 325% of the integrated intensity of BAM.

  According to the method of the present invention, since the excitation light has a practically sufficient luminance at a wavelength of about 400 nm, it can be used as a phosphor emitting blue light with a near-ultraviolet LED in the vicinity of a wavelength of 400 nm.

Claims (3)

A method for producing an Eu element-added barium thiosilicate phosphor comprising an alkaline earth metal, silicon, sulfur, and Eu element imparting fluorescence,
A first step of synthesizing Ba ₂ SiO _{4 in} which Eu elements are uniformly dispersed;
A second step in which Ba ₂ SiO _{4 in} which the Eu element obtained in the first step is uniformly dispersed is heat-treated in an inert gas containing carbon disulfide and then reduced and sulfided;
A process for producing a Eu element-added barium thiosilicate phosphor, comprising: A method for producing an Eu element-added barium thiosilicate phosphor comprising an alkaline earth metal, silicon, sulfur, and Eu element imparting fluorescence,
A first step of synthesizing a mixture of Ba ₂ SiO ₄ in which Eu element is uniformly dispersed, BaCO ₃ in which Eu element is uniformly dispersed, Ba (NO ₃ ) ₂ and SiO ₂ in which Eu element is uniformly dispersed;
A method for producing an Eu element-added barium thiosilicate phosphor, comprising: a second step of heat-treating the mixture in an inert gas containing carbon disulfide and reducing and sulfidizing the mixture. In the second step, Ba ₂ SiO ₄ in which the Eu element obtained in the first step is uniformly dispersed, or the mixture is heated to 900 to 1090 ° C. in an inert gas atmosphere containing carbon disulfide. The method for producing an Eu element-added barium thiosilicate phosphor according to claim 1 or 2 , wherein the reduction and sulfidation is performed by heat treatment according to temperature.

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