SEMICONDUCTOR PARTICLES USED IN WATER DECOMPOSITION PHOTOCATALYST, PHOTOCATALYST USING THE SAME, AND METHODS OF SYNTHESIZING THEM

Abstract

In a photocatalyst which is obtained by adding a co-catalyst to semiconductor particles containing strontium titanate and which causes a water decomposition reaction in which water molecules are decomposed into oxygen molecules and hydrogen molecules according to light emission, the semiconductor particles are doped with barium or additionally with scandium. A method of synthesizing a semiconductor for the photocatalyst includes a process of synthesizing semiconductor particles containing strontium titanate doped with barium by mixing barium titanate or additionally with scandium oxide into strontium chloride or mixing strontium titanate or additionally scandium oxide into strontium chloride and barium chloride and performing firing.

Claims

1. Semiconductor particles containing strontium titanate to which a co-catalyst is added and used as a photocatalyst that causes a water decomposition reaction in which water molecules are decomposed into oxygen molecules and hydrogen molecules according to light emission, and in which strontium titanate is doped with barium.

2. The semiconductor particles according to claim 1, wherein strontium titanate is additionally doped with scandium.

3. The semiconductor particles according to claim 2, wherein the content of barium is 0.04 parts by weight to 5 parts by weight, and the content of scandium is 0.1 parts by weight to 1 part by weight with respect to 100 parts by weight of strontium titanate.

4. The semiconductor particles according to claim 3, wherein the content of barium is 0.1 parts by weight to 2 parts by weight.

5. The semiconductor particles according to claim 1, which are substantially free of aluminum.

6. The semiconductor particles according to claim 1, wherein the content of aluminum with respect to 100 parts by weight of strontium titanate is 1 part by weight or less.

7. A photocatalyst obtained by adding a co-catalyst to the semiconductor particles according to claim 1, wherein the co-catalyst is rhodium-chromium oxide (Rh/Cr.sub.2O.sub.3) or cobalt hydroxide oxide (CoOOH).

8. The photocatalyst according to claim 7, wherein the co-catalyst is added to the surface of the semiconductor particles dispersed in water by photoelectrodepositing.

9. A photocatalyst obtained by adding a co-catalyst to the semiconductor particles according to claim 5, wherein the co-catalyst is rhodium-chromium oxide (Rh/Cr.sub.2O.sub.3) or cobalt hydroxide oxide (CoOOH).

10. A photocatalyst obtained by adding a co-catalyst to the semiconductor particles according to claim 6, wherein the co-catalyst is rhodium-chromium oxide (Rh/Cr.sub.2O.sub.3) or cobalt hydroxide oxide (CoOOH).

11. A method of synthesizing semiconductor particles used in a photocatalyst which is obtained by adding a co-catalyst to semiconductor particles containing strontium titanate and which causes a water decomposition reaction in which water molecules are decomposed into oxygen molecules and hydrogen molecules according to light emission, the method comprising a process of synthesizing the semiconductor particles containing strontium titanate doped with barium by mixing barium titanate (BaTiO.sub.3) into strontium chloride (SrCl.sub.2) and performing firing.

12. The method according to claim 11, wherein, in the process of synthesizing the semiconductor particles, the semiconductor particles are doped with barium and scandium by additionally mixing scandium oxide (Sc.sub.2O.sub.3) into the strontium chloride and performing firing.

13. The method according to claim 12, wherein, in the process of synthesizing the semiconductor particles, 500 parts by mole to 2,000 parts by mole of strontium chloride and 0.1 parts by mole to 5 parts by mole of scandium oxide with respect to 100 parts by mole of barium titanate are mixed in and fired to synthesize the semiconductor particles.

14. A method of synthesizing semiconductor particles used in a photocatalyst which is obtained by adding a co-catalyst to semiconductor particles containing strontium titanate and which causes a water decomposition reaction in which water molecules are decomposed into oxygen molecules and hydrogen molecules according to light emission, the method comprising a process of synthesizing the semiconductor particles containing strontium titanate doped with barium and scandium by mixing strontium titanate (SrTiO.sub.3) and scandium oxide (Sc.sub.2O.sub.3) into a mixture containing strontium chloride (SrCl.sub.2) and barium chloride (BaCl.sub.2) and performing firing.

15. The method according to claim 14, wherein, in the process of synthesizing the semiconductor particles, the semiconductor particles are additionally doped with aluminum by additionally mixing aluminum oxide (Al.sub.2O.sub.3) into the mixture containing strontium chloride and barium chloride and performing firing.

16. The method according to claim 14, wherein, in the process of synthesizing the semiconductor particles, the semiconductor particles are synthesized by mixing a mixture containing strontium chloride and barium chloride at a molar ratio of 1:9 to 9:1 as a mixture of 1,000 parts by mole of strontium chloride and barium chloride with respect to 100 parts by mole of strontium titanate, 0.1 parts by mole to 5 parts by mole of scandium oxide (Sc.sub.2O.sub.3) and 0 parts by mole to 5 parts by mole of aluminum oxide and performing firing.

17. The method according to claim 11, wherein, in the process of synthesizing semiconductor particles, a firing temperature is 1,000? C. to 1,200? C., and a firing time is 10 hours to 30 hours.

18. A method of synthesizing a photocatalyst that causes a water decomposition reaction in which water molecules are decomposed into oxygen molecules and hydrogen molecules according to light emission using the semiconductor particles synthesized by the method according to claim 11, the method comprising a process of adding the co-catalyst to the surface of the semiconductor particles dispersed in water.

19. The method according to claim 18, wherein the co-catalyst is rhodium-chromium oxide (Rh/Cr.sub.2O.sub.3) or cobalt hydroxide oxide (CoOOH).

20. The method according to claim 19, wherein, in the process of adding the co-catalyst, the co-catalyst is added to the surface of the semiconductor particles dispersed in water by photoelectrodepositing.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like signs denote like elements, and wherein:

[0020] FIG. 1 is a schematic view illustrating processes of methods of synthesizing semiconductor particles according to the present disclosure and a photocatalyst using the same;

[0021] FIG. 2A shows values of the quantum efficiency obtained from the photocatalyst using the semiconductor particles synthesized according to the method of the present disclosure when the content of barium with respect to strontium titanate is changed;

[0022] FIG. 2B shows values of the quantum efficiency obtained from the photocatalyst using the semiconductor particles synthesized according to the method of the present disclosure when the content of scandium with respect to strontium titanate is changed in the presence of barium and aluminum;

[0023] FIG. 3A shows values of the quantum efficiency obtained from the photocatalyst using the semiconductor particles synthesized according to the method of the present disclosure when the temperature during firing in synthesis of semiconductor particles is changed; and

[0024] FIG. 3B shows values of the quantum efficiency obtained from the photocatalyst using the semiconductor particles synthesized according to the method of the present disclosure when the time during firing in synthesis of semiconductor particles is changed. Numbers in the bar graph indicate the number of experiments under the conditions.

DETAILED DESCRIPTION OF EMBODIMENTS

[0025] Methods of Synthesizing Semiconductor Particles for Water Decomposition Reaction Photocatalyst and Photocatalyst

[0026] Semiconductor particles for a water decomposition reaction photocatalyst according to the present embodiment are synthesized by heating a raw material mixture in which strontium chloride (SrCl.sub.2) is mixed with barium titanate (BaTiO.sub.3) or additionally with scandium oxide (Sc.sub.2O.sub.3) and aluminum oxide (Al.sub.2O.sub.3) (a raw material mixture in a first synthesis method) or a raw material mixture in which a mixture containing strontium chloride (SrCl.sub.2) and barium chloride (BaCl.sub.2) is mixed with strontium titanate (SrTiO.sub.3) or additionally with scandium oxide (Sc.sub.2O.sub.3), and aluminum oxide (Al.sub.2O.sub.3) (a raw material mixture in a second synthesis method) to a temperature at which SrCl.sub.2 and BaCl.sub.2 melt and become a liquid (where, a temperature at which BaTiO.sub.3, SrTiO.sub.3, Sc.sub.2O.sub.3, and Al.sub.2O.sub.3 do not melt), doping SrTiO.sub.3 with barium atoms (Ba) or additionally with scandium atoms (Sc) or additionally with aluminum atoms (Al), and converting SrTiO.sub.3 into a semiconductor (flux method). Then, the photocatalyst is synthesized by adding a co-catalyst substance to the semiconductor particles obtained by the flux method, for example, a photoelectrodepositing method (also referred to as photodepositing method).

[0027] More specifically, with reference to FIG. 1, in the present embodiment, semiconductor particles are prepared by two synthesis methods with different starting materials. In the first synthesis method, a large amount of SrCl.sub.2 powder is mixed with BaTiO.sub.3 powder or additionally mixed with Sc.sub.2O.sub.3 powder and Al.sub.2O.sub.3 powder. Preferable proportions of respective powders are as follows. [0028] with respect to 100 parts by mole of BaTiO.sub.3, [0029] SrCl.sub.2: 500 parts by mole to 2,000 parts by mole [0030] Sc.sub.2O.sub.3: 0.1 parts by mole to 5 parts by mole [0031] Al.sub.2O.sub.3: 0 parts by mole to 5 parts by mole (Al.sub.2O.sub.3 may not be contained)

[0032] In addition, in the second synthesis method, a mixture containing a large amount of SrCl.sub.2 powder and BaCl.sub.2 powder is mixed with SrTiO.sub.3 powder or additionally with Sc.sub.2O.sub.3 powder and Al.sub.2O.sub.3 powder. Preferable proportions of respective powders are as follows. [0033] with respect to 100 parts by mole of SrTiO.sub.3, [0034] SrCl.sub.2+BaCl.sub.2: 1,000 parts by mole [0035] (the molar ratio of SrCl.sub.2 and BaCl.sub.2 is 1:9 to 9:1) [0036] Sc.sub.2O.sub.3: 0.1 parts by mole to 5 parts by mole [0037] Al.sub.2O.sub.3: 0 parts by mole to 5 parts by mole (Al.sub.2O.sub.3 may not be contained)

[0038] Mixing of the above powders may be performed, for example, by grinding in an agate mortar (M) (about 30 minutes).

[0039] Thereafter, the raw material mixture powder is transferred to a firing crucible, for example, an alumina crucible (C), and fired in a firing furnace (H) ((B) in FIG. 1). In this process, as described above, the firing temperature may be a temperature at which SrCl.sub.2 melts and becomes a liquid (874? C. or higher), a temperature at which SrCl.sub.2 and BaCl.sub.2 melt and become a liquid (962? C. or higher) or a temperature at which BaTiO.sub.3, SrTiO.sub.3, Sc.sub.2O.sub.3, and Al.sub.2O.sub.3 do not melt (1,625? C. or lower), and as described below, according to experiments performed by the inventors of the present disclosure and the like, the firing temperature may be, for example, about 1,000? C. to 1,200? C., and preferably 1,100? C. to 1,200? C. In addition, the firing time for which the raw material mixture is exposed at the above temperature is a time sufficient for SrTiO.sub.3 to be doped with Ba or additionally with Sc or additionally with Al and converting SrTiO.sub.3 into a semiconductor, and according to experiments performed by the inventors of the present disclosure and the like, as described below, the firing time may be 10 hours to 30 hours and preferably about 30 hours.

[0040] After the firing process, when the fired product is cooled to room temperature, water (distilled water may be used) is added to the crucible (C), the fired product in the crucible is dispersed as particles in water while stirring by applying ultrasonic waves with an ultrasonic stirrer or the like, suction filtration is additionally performed, and thus the fired product may be collected. Such a particulate fired product is semiconductor particles P (BaSrTiO.sub.3, BaScSrTiO.sub.3 or AlBaScSrTiO.sub.3, AlBaSrTiO.sub.3) for the photocatalyst according to the present embodiment. Then, the collected semiconductor particles P may be washed with water. Such washing may be performed until the pH of washing water is 7, and washing water is free of chlorine. Thus, the semiconductor particles may be dried after washing.

[0041] In order for the above semiconductor particles to function as a photocatalyst, a co-catalyst is added to the crystal planes of semiconductor particles. It is thought that, after charges (electrons and holes) generated in semiconductor particles according to light emission in the water decomposition reaction with light move to the surface of semiconductor particles, such a co-catalyst prevents these charges from returning into the semiconductor particles again. In the present embodiment, a co-catalyst may be added to semiconductor particles by an arbitrary method, and typically, as already mentioned, as in T. Takata, 8 others, Nature, volume 581, pp. 411-414, 2020, by a photoelectrodepositing method, a co-catalyst is precipitated in the crystal planes of the semiconductor particles dispersed in water, and thus the co-catalyst may be added to the semiconductor particles. Specifically, first, semiconductor particles are dispersed in water in a transparent container such as a glass container ((C) in FIG. 1). Here, ultrasonic waves may be applied to water in which semiconductor particles are dispersed (semiconductor particle dispersion solution) so that the semiconductor particles are uniformly dispersed. Thereafter, treatments of adding salts as a raw material of the co-catalyst, emitting light L is, and precipitating metal oxides as a co-catalyst on the surface of the semiconductor particles P are performed ((D) in FIG. 1).

[0042] More specifically, as a co-catalyst added to the surface of the semiconductor particles P, as in T. Takata, 8 others, Nature, volume 581, pp. 411-414, 2020, when rhodium-chromium oxide (Rh/Cr.sub.2O.sub.3) or cobalt hydroxide oxide (CoOOH) are used, the process may be performed as follows. That is, first, a rhodium chloride (RhCl.sub.3) aqueous solution is added to a semiconductor particle dispersion solution so that the amount of rhodium (Rh) is 0.1 wt % with respect to the amount of the semiconductor particles, and light from a xenon lamp (300 W, 20 mA) is emitted to the semiconductor particle dispersion solution under atmospheric pressure for 10 minutes. Next, a potassium chromate (K.sub.2CrO.sub.4) aqueous solution is added to the semiconductor particle dispersion solution so that the amount of chromium (Cr) is 0.05 wt % with respect to the amount of the semiconductor particles, and light from a xenon lamp (300 W, 20 mA) is emitted under atmospheric pressure for 5 minutes. Then, a cobalt nitrate (Co(NO.sub.3).sub.2) aqueous solution is added to the semiconductor particle dispersion solution so that the amount of cobalt (Co) is 0.05 wt % with respect to the amount of the semiconductor particles, and light from a xenon lamp (300 W, 20 mA) is emitted under atmospheric pressure for 5 minutes. Then, as schematically shown in (D) in FIG. 1, RhCr oxide and Co oxyhydroxide are adhered to the surface of the semiconductor particles P, and thus the prepared compound functions as a photocatalyst that causes a water decomposition reaction with light. Here, in the process of adding a co-catalyst to the surface of the semiconductor particles by a photoelectrodepositing method, the concentration of salts for the co-catalyst added to the semiconductor particle dispersion solution may be appropriately adjusted. According to experiments performed by the inventors, for example, it is found that, when the concentration of salts for the co-catalyst is 4 times the above concentration, the quantum efficiency decreases significantly, and thus such a salt concentration is preferably adjusted so that the concentration does not become excessive. In addition, addition of a co-catalyst to the surface of the semiconductor particles may be performed by an impregnation method (adding salts to the dispersion solution and applying heat) in addition to the photoelectrodepositing method.

[0043] The performance of the semiconductor particles prepared by the synthesis method according to the present embodiment is evaluated by measuring the quantum efficiency [number of hydrogen molecules?2/number of emitted photons] in the water decomposition reaction with light when a co-catalyst is added to impart photocatalytic properties. Regarding the performance of such semiconductor particles, as will be understood from the following experiment example, in the composition (detected through ICP-MS) of the semiconductor particles, when the content of barium is 0.1 parts by weight to 2 parts by weight with respect to 100 parts by weight of strontium titanate, a quantum efficiency of about 70% or more is stably provided (when the content of scandium is 0.1 parts by weight). In addition, in the composition of the semiconductor particles, when 0.7 parts by weight to 0.8 parts by weight of barium is present with respect to 100 parts by weight of strontium titanate, if the content of scandium is 0.1 parts by weight to 1 part by weight, a quantum efficiency of more than 70% is obtained (when there is no scandium, the quantum efficiency is about 30%). Here, regarding the presence of aluminum, no significant difference in the quantum efficiency is observed under conditions in which the content of aluminum is less than 1 part by weight with respect to 100 parts by weight of strontium titanate. In addition, no significant difference in the quantum efficiency is observed between when the starting material is obtained in the first synthesis method and when the starting material is obtained in the second synthesis method. Therefore, according to the present embodiment, when semiconductor particles in which strontium titanate is doped with barium or additionally with scandium are synthesized and a photocatalyst is prepared using the same, it is possible to provide semiconductor particles and a photocatalyst that stably provide higher quantum efficiency.

Experiment Example

[0044] According to the teachings of the present embodiment, semiconductor particles in which strontium titanate was doped with barium or additionally with scandium or aluminum and a photocatalyst using the same were synthesized, the quantum efficiency of the photocatalyst was measured, and the effectiveness of the present embodiment was verified. Here, it should be understood that the following experiment example shows effectiveness of the present embodiment and does not limit the scope of the present disclosure.

[0045] Semiconductor particles were synthesized according to the above process. Specifically, first, SrCl.sub.2 powder, BaTiO.sub.3 powder, Sc.sub.2O.sub.3 powder and Al.sub.2O.sub.3 powder at various proportions in the first synthesis method and SrCl.sub.2 powder, BaCl.sub.2 powder, SrTiO.sub.3 powder, Sc.sub.2O.sub.3 powder and Al.sub.2O.sub.3 powder at various proportions in the second synthesis method were ground and mixed in an agate mortar for 30 minutes. The powder mixture was transferred to an alumina crucible and then fired in a firing furnace by setting various firing temperatures and firing times. Here, in the firing process, the temperature was raised from room temperature to the firing temperature in 2 hours, and after the firing time was elapsed, the sample was cooled to room temperature over 6 hours. After cooling, distilled water was added to the crucible containing the fired product, ultrasonic waves were applied with an ultrasonic stirrer and stirring was performed, and the fired product in the crucible (the material adhered to the inner wall of the crucible was also dispersed) was dispersed in water as particles and collected by suction filtration. Then, the collected particulate fired product was washed with distilled water. In washing, the pH of the washing water was checked using pH test paper, the presence of chlorine in the washing water was checked for whether silver chloride was generated by adding 0.1 M silver nitrate to the washing water, and washing was performed until the pH of the washing water reached 7 and chlorine was no longer detected. Then, the particulate fired product after washing, that is, the semiconductor particles, were dried at 70? C. The composition of the semiconductor particles was detected through ICP-MS.

[0046] In the preparation of the photocatalyst using the semiconductor particles, in a heat-resistant glass container (400 ml), 100 mg of semiconductor particles powder was dispersed in 100 ml of distilled water. Then, first, a rhodium chloride (RhCl.sub.3) aqueous solution was added to a semiconductor particle dispersion solution so that the amount of rhodium (Rh) was 0.1 wt % with respect to the amount of the semiconductor particles, light from a xenon lamp (300 W, 20 mA) was emitted to the semiconductor particle dispersion solution under atmospheric pressure for 10 minutes, and next, a potassium chromate (K.sub.2CrO.sub.4) aqueous solution was added to the semiconductor particle dispersion solution so that the amount of chromium (Cr) was 0.05 wt % with respect to the amount of the semiconductor particles, and in the same manner as above, light from a xenon lamp (300 W, mA) was emitted to the semiconductor particle dispersion solution under atmospheric pressure for 5 minutes, and finally, a cobalt nitrate (Co(NO.sub.3).sub.2) aqueous solution was added to the semiconductor particle dispersion solution so that the amount of cobalt (Co) was 0.05 wt % with respect to the amount of the semiconductor particles, and in the same manner as above, light from a xenon lamp (300 W, 20 mA) was emitted to the semiconductor particle dispersion solution under atmospheric pressure for 5 minutes. Here, light from a xenon lamp was emitted while the glass container was covered with a quartz disk. Thus, the semiconductor particle dispersion solution after the treatment was directly used as a solution in which a photocatalyst was dispersed (photocatalyst dispersion solution) for measurement of the quantum efficiency.

[0047] In the measurement of the quantum efficiency of the photocatalyst, first, the glass container containing the photocatalyst dispersion solution was degassed with a vacuum pump and then filled with argon gas, and thus air in the glass container was replaced with argon gas. Thereafter, the glass container was connected to a gas chromatograph through a glass pipe, light from a xenon lamp (300 W, 20 mA) was emitted to the photocatalyst dispersion solution in the glass container through a 365 nm bandpass filter, and a water decomposition reaction was caused to generate hydrogen gas. In the detection of the amount of hydrogen gas generated, the hydrogen gas generated in the glass pipe was accumulated when light emission was performed for 2 hours, the accumulated gas was introduced into the gas chromatograph, and the amount of hydrogen gas was detected (measurement was performed every 20 minutes). In the detection of the amount of hydrogen gas in the chromatograph, using a standard gas with a known number of moles of hydrogen gas in advance, a calibration curve between the number of moles of hydrogen and an area of a detection data part corresponding to hydrogen gas was created, and using this calibration curve, the number of moles generated was determined from the area of the detection data part of hydrogen gas introduced from the glass pipe to the gas chromatograph. On the other hand, regarding the number of photons emitted to the photocatalyst dispersion solution in the glass container, the wattage P (energy amount per unit time) of total light emitted to the photocatalyst dispersion solution in the glass container used for measurement was measured with a photodiode sensor, and the number of photons I incident on the photocatalyst dispersion solution per unit time was calculated by the following formula.

I(/s)=P(W)??(m)/[h(J.Math.s)?c(m/s)]

[0048] Here, ? is the wavelength of emitted light, h is the Planck's constant, and c is the speed of light. Thus, the quantum efficiency was calculated by the following formula.

quantum efficiency (%)=n(/s)?NA?2/I?100

[0049] Here, n is the number of moles of hydrogen gas generated per unit time, and NA is the Avogadro's number.

[0050] As a result, first, the quantum efficiencies measured with photocatalysts prepared using the semiconductor particles synthesized by variously changing the content of barium are shown in FIG. 2A. Here, in the drawing, the content of barium in the semiconductor particles with respect to 100 parts by weight of strontium titanate is expressed in parts by weight. In addition, in the composition, the content of scandium was 0.1 parts by weight (not including aluminum). The firing time during firing was set to 30 hours, and the firing temperature was set to 1,150? C. As can be understood with reference to the drawing, when the content of barium was 0.04 parts by weight to 5 parts by weight, the quantum efficiency was about 70% or more, and when the content of barium was 0.1 parts by weight to 2 parts by weight, a high quantum efficiency value of 80% to 90% was stably obtained. Therefore, it was shown that, when the content of barium in the semiconductor particles with respect to 100 parts by weight of strontium titanate was 0.04 parts by weight to 5 parts by weight, and more preferably, when the content of barium was 0.1 parts by weight to 2 parts by weight, a photocatalyst that provides high quantum efficiency could be obtained.

[0051] The quantum efficiencies measured with the photocatalysts prepared using semiconductor particles synthesized by changing the content of scandium in the presence of barium and aluminum are shown in FIG. 2B. Here, with respect to 100 parts by weight of strontium titanate, the content of barium was 0.7 parts by weight to 0.8 parts by weight, and the content of aluminum was 0.2 parts by weight. The firing time during firing was 30 hours, and the firing temperature was 1,150? C. Based on the results in the drawing, it was shown that, even without scandium, a quantum efficiency of about 30% could be obtained, but when the content of scandium was 0.1 parts by weight to 1 part by weight, a photocatalyst with a high quantum efficiency of more than 70% or 80% could be obtained. In addition, with reference to the results in FIG. 2A together, it can be understood that, in the semiconductor particles, when barium of about 0.1 parts by weight to 2 parts by weight was present, the presence of aluminum on the order of 0.1 parts by weight did not make a significant difference in the quantum efficiency of the photocatalyst.

[0052] Furthermore, the quantum efficiency of the photocatalyst using the semiconductor particles (with respect to 100 parts by weight of strontium titanate, the content of barium was 0.75 parts by weight, the content of scandium was 0.58 parts by weight, and the content of aluminum was 0.18 parts by weight) synthesized by the first synthesis method was 82%, and the quantum efficiency of the photocatalyst using the semiconductor particles (with respect to 100 parts by weight of strontium titanate, the content of barium was 0.75 parts by weight, the content of scandium was 0.62 parts by weight, and the content of aluminum was 0.14 parts by weight) synthesized by the second synthesis method was 84%. Therefore, it can be understood that there was no significant difference between the photocatalyst using the semiconductor particles synthesized by the first synthesis method and the photocatalyst using the semiconductor particles synthesized by the second synthesis method.

[0053] Next, the quantum efficiencies measured with photocatalysts prepared using the semiconductor particles synthesized by variously changing the firing temperature and the firing time during firing of the powder mixture are shown in FIG. 3A and FIG. 3B. Here, the semiconductor particles were prepared so that the composition contained 0.3 parts by weight of barium and 0.1 parts by weight of scandium with respect to 100 parts by weight of strontium titanate. First, with reference to FIG. 3A, if the firing time was constant (30 hours), when the firing temperature was 1,000? C. to 1,200? C., the quantum efficiency exceeded about 70%, and when the firing temperature was 1,100? C. to 1,200? C., the quantum efficiency exceeded about 80%, and when the firing temperature was 1,150? C., the quantum efficiency was maximized. On the other hand, with reference to FIG. 3B, when the firing temperature was constant (1,150? C.), the quantum efficiency exceeded 80% within a firing time range of 10 hours to 30 hours, and no significant difference was observed within this time range. Therefore, it was shown that, when the firing time was in a range of 10 hours to 30 hours and the firing temperature was 1,000? C. to 1,200? C., and more preferably 1,100? C. to 1,200? C., it was possible to synthesize semiconductor particles that stably provide high quantum efficiency.

[0054] It can be clearly understood that the above description is related to the embodiments of the present disclosure, and those skilled in the art can easily make many modifications and changes, and the present disclosure is not limited to the above exemplified embodiments, but can be applied to various devices without departing from the concept of the present disclosure.