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Zn2SiO4:Mn phosphor particles prepared by spray pyrolysis using a filter expansion aerosol generator
Pergamon
Materials Research Bulletin 35 (2000) 1143–1151
Zn2SiO4:Mn phosphor particles prepared by spray pyrolysis using a filter expansion aerosol generator Y.C. Kang, S.B. Park* Department of Chemical Engineering, Korea Advanced Institute of Science and Technology, 373-1, Kusongdong, Yusong-gu, Taejon, 305-701, Korea (Refereed) Received 17 May 1999; accepted 23 August 1999
Abstract Manganese-doped zinc silicate phosphor particles were prepared by spray pyrolysis using FEAG (Filter Expansion Aerosol Generator) process. The characteristics of cathodoluminescence, crystallinity, and morphology of Zn2SiO4:Mn particles were investigated. The as-prepared and calcined particles were spherical shape and 1 micrometer in diameter, and aggregation between particles was not observed even after calcination at high temperature. The particles prepared at 600°C had amorphous phase, and zinc oxide peaks appeared at 700°C. The peaks of the -Zn2SiO4 with orthorhombic structure was obtained at 1000°C. Pure phase willemite structure was obtained after calcination at 1200°C for 5 h when adding the 80 –90% of stoichiometric amount of zinc nitrate. The maximum cathodoluminescence (CL) intensity of particles was obtained at 1.3 mol% doping concentration of Mn. The particles calcined at 1200°C for 5 h has the maximum CL intensity of 198 cd/m2. © 2000 Elsevier Science Ltd. All rights reserved. Keywords: A. Ceramics; A. Composites; B. Chemical synthesis; D. Luminescence; D. Optical properties
Introduction Various types of multicomponent oxide phosphor particles were widely studied for improved performance in displays and lamps. The mean size of particles is very important factor for high resolution and high efficiency in displays [1,2]. Small particles improve aging
* Corresponding author. Fax: 82-42-869-3910. E-mail address: [email protected] (S.B. Park). 0025-5408/00/$ – see front matter © 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 0 2 5 - 5 4 0 8 ( 0 0 ) 0 0 3 0 6 - 8
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by forming a densely packed phosphor layer. It has been predicted that the optimum phosphor characteristics can be obtained with particle sizes on the order of 1 m. Spherical morphology is also required for high brightness and high resolution of displays. If the phosphor particles have spherical shape, scattering of light emitted from phosphors become diminished. Additionally, spherical phosphor particles are suitable for making high packing density phosphor layer [3,4]. Manganese-doped willemite, Zn2SiO4, is used as green phosphor in fluorescent lamps, cathode ray tubes, and flat panel displays [5–9] Zn2SiO4:Mn particles have been mainly prepared by solid state reactions. In solid-state reactions, it is difficult to prepare phase-pure willemite because of the difference in volatilities of zinc oxide and silicon oxide. In addition, high reaction temperature, long heating time, and milling process are required. Therefore, agglomerated particles with irregular shape and large size are produced by the solid-state reaction method. To overcome the disadvantage of the solid-state reaction method, various liquid solution processes have been introduced for preparing Zn2SiO4:Mn phosphor [7–9]. These liquid solution processes require lower preparation temperatures than that of the solid-state reaction process, but particles of irregular and agglomerated morphology are still produced. Recently, gas phase reaction processes were applied to the preparation of multicomponent phosphor materials. In general, gas phase reactions produce particles of fine size and spherical morphology. Sievers et al. [1] prepared Y2O3:Eu phosphors by CO2-assisted aerosolization. In this technique, supercritical CO2 is combined with aqueous solutions of water-soluble metal nitrates or acetates in a low-dead-volume tee to form emulsions at 10 MPa. Spherical and submicron phosphor particles are formed by rapid desolvation of the aerosol in a tubular furnace by dehydration and pyrolysis. Bihari et al. [10] prepared Y2O3:Eu nanocrystalline phosphors by gas-phase condensation by using CO2 laser heating of ceramic pellets. It should be noted that these gas phase reactions are currently confined to the preparation of phosphors with simple composition. In Kang et al.’s works [11–13], ultrasonic spray pyrolysis, which is one of the gas phase reaction methods, was applied to the preparation of multicomponent phosphor materials. Spray pyrolysis is a method of producing particles, in which a misted stream of precursor solution is dried, precipitated, and decomposed in a tubular furnace reactor. Particles produced by spray pyrolysis are relatively uniform in size and composition because of microscale reaction within a droplet and the lack of milling process. In spray pyrolysis, the rare-earth dopants are well distributed inside host materials, so the produced particles are expected to have good luminescence characteristics compared with other solid or liquid processes. In this study, manganese-doped willemite, Zn2SiO4, phosphor particles were prepared by spray pyrolysis using the FEAG process [14]. Characteristics of particles such as phase purity, crystallinity, mean size, morphology, and cathodoluminescence (CL) were investigated.
2. Experimental The apparatus used in this work was a filter expansion aerosol generator (FEAG), of which details have appeared elsewhere [14,15]. In the FEAG process, the solutions are atomized
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into droplets of 2 m at 5 ml/min and delivered into a hot-wall reactor at 60 Torr. As the aerosol stream passes through the reactor, the solvent evaporates and the metal salts decompose into individual oxide particles. The reaction of individual particles into single phase multicomponent oxide particles then follows in the high temperature of the reactor. The starting solutions were prepared from zinc nitrate, TEOS (tetraethyl orthosilicate), and manganese acetate. Small amount of nitric acid was added for clear solution. The reaction temperatures were increased from 700 to 1000°C. The as-prepared particles were calcined above 1000°C for crystallization and activation of phosphor materials. To find optimum post-treatment conditions, the particles prepared at 900°C were calcined at each temperatures of 1000, 1100, 1200, and 1300°C. The prepared particles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and centrifugal particle size analysis (CPSA). Cathodoluminescence and chromaticity of the particles were measured by a Minolta CS-100.
3. Results and discussions Fig. 1 shows the SEM photographs of as-prepared and calcined Zn2SiO4:Mn particles. The as-prepared particles at 900°C were calcined at 1000° for 5 h. Both particles had spherical shape, and agglomeration was not apparent even after calcination at high temperature. The mean size of Zn2SiO4:Mn particles prepared from precursor solution of 0.3 M was 1 m. XRD spectra of the particles prepared from the FEAG process was shown in Fig. 2. The particles prepared at 600°C had amorphous phase, and zinc oxide peaks appeared at 700°C. The peaks of the -Zn2SiO4 with orthorhombic structure was obtained at 1000°C. In Fig. 3, XRD spectra of calcined particles were shown. The calcined particles above 800°C for 5 hours had crystalline phase of willemite. The as-prepared particles had poor crystallinity of -Zn2SiO4 and zinc oxide because of the short residence time of particles inside the hot wall reactor. But each component is distributed well inside a particle. Therefore, willemite structure was obtained at lower calcination temperatures than that of solid-state reaction method. On the other hand, ZnO peaks as impurity were shown after calcination below 1000°C. Because of the low boiling point (165°C) of TEOS, some TEOS in droplets evaporated before pyrolysis into SiO2. Due to the volatility of zinc oxide, the XRD intensities of zinc oxide peaks were reduced when the calcination temperature was above 1000°C, and pure phase willemite structure was obtained after calcination at 1200°C for 5 h. The crystallite size of particles calculated from Scherrer’s formula was varied from 290 to 430 nm when the calcination temperature was changed from 900 to 1400°C. The maximum crystallite size was obtained at 1200°C, and the crystallinity of the particles was decreased with increasing the calcination temperature above 1200°C. At high temperatures above 1300°C, the willemite structure destroyed because zinc oxide in the willemite structure evaporated, and the crystallinity of particles decreased. Fig. 4 shows the XRD spectra of particles prepared from different ratios of zinc nitrate and TEOS. The as-prepared particles at 900°C were calcined at 1000°C for 10 h. When adding
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Fig. 1. SEM photographs of as-prepared and calcined particles.
the 80 –90 mol% of the stoichiometric amount of zinc nitrate, pure phase willemite and the highest crystallinity was achieved. Fig. 5 shows the excitation and emission spectra of Zn2SiO4:Mn particles. For the measurement of PL spectra, the as-prepared particles with 1.3 mol% doping of Mn were calcined at 1200°C for 5 h. The particles absorbed excitation energy in the range from 220 nm to 300 nm, and the maximum excitation wavelength was near 253 nm. The main emission peak of particles was 527 nm, resulting in a green emission. The CL intensities of Zn2SiO4:Mn particles were measured when it was excited by field emitter arrays at 400 V and 1 mA/min2 in a high vacuum chamber(10⫺6 Torr). To
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Fig. 2. XRD spectra of particles at different preparation temperatures. (P600: Preparation temperature ⫽ 600°C).
find the optimum CL intensity, the amount of zinc nitrate in precursor solution was changed from 100 to 60% relative to the stoichiometric amount. The manganese concentration was 1 mol% and the as-prepared particles were calcined at 1000°C for 10 h. In Fig. 6, the CL intensities of Zn2SiO4:Mn particles were varied from 85.9 to 131 cd/m2
Fig. 3. XRD spectra of particles calcined at different temperatures. (C700: Calcination temperature ⫽ 700°C).
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Fig. 4. XRD spectra of particles prepared from different ratios of zinc nitrate and TEOS.
when the amount of zinc nitrate was changed from 100 to 60% relative to the stoichiometric amount. The particles prepared from precursor solution with 80% zinc nitrate relative to the stoichiometric amount had the highest CL intensity. Therefore, the amount of zinc nitrate in precursor solution was fixed at 80% of the stoichiometric amount for the best luminescence of phosphor particles. In Fig. 7, the CL intensities of Zn2SiO4:Mn particles at different manganese concentrations were shown. When the doping concentration of Mn was changed from 0.75 to 2 mol%, the maximum CL intensity was obtained at 1.3 mol% doping concentration of Mn. In Fig. 8, calcination temperature for the crystallization and activation of Zn2SiO4:Mn particles with 1.5 mol% of Mn was changed from 900 to 1300°C to examine its effect on the CL intensity. The particles calcined at 1200°C for 5 h have the maximum CL intensity of 198 cd/m2. This result of CL intensities of particles is well coincided with the results of XRD. In the XRD spectra of particles, the particles calcined at 1200°C had the highest crystallinity of willemite. Generally, particles with large crystallite size have higher brightness than that of particles with small crystallite size, because of low concentration of defects, which act as sites for the nonradiative recombination of electron-hole pairs.
4. Conclusions Mn-doped zinc silicate phosphor particles with spherical shape, nonaggregation, and submicron size were prepared by spray pyrolysis using the FEAG process. Spray pyrolysis had many advantages for the preparation of multicomponent phosphor particles. Rare-earth
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Fig. 5. Excitation and emission spectra of Zn2SiO4:Mn particles.
Fig. 6. CL intensities of particles prepared from different ratios of zinc nitrate and TEOS.
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Fig. 7. CL intensities of particles at different doping concentrations of Mn.
doped multicomponent phosphor particles with pure phase could be prepared at lower temperature than that of the solid-state reaction. The particles were relatively uniform in size and composition because of the microscale reaction within a droplet and the lack of milling process in the spray pyrolysis process. In addition, calcined particles had nonagglomeration at the calcination conditions for optimum brightness.
Fig. 8. CL intensities of particles at different calcination temperatures.
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References [1] R.E. Sievers, P.D. Milewski, C.Y. Xu, B.A. Watkins, Proceedings of Third International Conference on the Science and Technology of Display Phosphors, 1997, p. 303. [2] Y.D. Jiang, Z.L. Wang, F. Zhang, H.P. Paris, C.J. Summers, Proceedings of Third International Conference on the Science and Technology of Display Phosphors, 1997, p. 261. [3] S. Oshio, K. Kitamura, T. Shigeta, S. Horii, T. Matsuoka, T. Kanda, Proceedings of International Display Workshops, 1997, p. 621. [4] S. Oshio, K. Kitamura, T. Shigeta, S. Horii, T. Matsuoka, S. Tanaka, H. Kobayashi, J Electrochem Soc 146 (1) (1999) 392. [5] T. Miyata, T. Minami, K. Saikai, S. Takata, J Lumin 60 – 61 (1994) 926. [6] C. Barthou, J. Benoit, P. Benalloul, A. Morell, J Electrochem Soc 141 (2) (1994) 524. [7] I.F. Chang, J.W. Brownlow, T.I. Sun, J.S. Wilson, J Electochem Soc 136 (11) (1989) 3532. [8] R. Morimo, K. Matae, Mater Res Bull 24 (1989) 175. [9] Q.H. Li, S. Komarneni, R. Roy, J Mater Sci 30 (1996) 2358. [10] B. Bihari, H. Eilers, B.M. Tissue, J Lumin 75 (1997) 1. [11] Y.C. Kang, S.B. Park, I.W. Lenggoro, K. Okuyama, J Phys Chem Solids 60 (3) (1999) 379. [12] Y.C. Kang, I.W. Lenggoro, K. Okuyama, S.B. Park, J Electrochem Soc 146 (3) (1999) 1227. [13] Y.C. Kang, I.W. Lenggoro, S.B. Park, K. Okuyama, J Solid State Chem 146 (1999) 168. [14] Y.C. Kang, S.B. Park, J Aerosol Sci 26 (7) (1995) 1131. [15] Y.C. Kang, S.B. Park, J Mater Sci 31 (1996) 2409.
Materials Research Bulletin 35 (2000) 1143–1151
Zn2SiO4:Mn phosphor particles prepared by spray pyrolysis using a filter expansion aerosol generator Y.C. Kang, S.B. Park* Department of Chemical Engineering, Korea Advanced Institute of Science and Technology, 373-1, Kusongdong, Yusong-gu, Taejon, 305-701, Korea (Refereed) Received 17 May 1999; accepted 23 August 1999
Abstract Manganese-doped zinc silicate phosphor particles were prepared by spray pyrolysis using FEAG (Filter Expansion Aerosol Generator) process. The characteristics of cathodoluminescence, crystallinity, and morphology of Zn2SiO4:Mn particles were investigated. The as-prepared and calcined particles were spherical shape and 1 micrometer in diameter, and aggregation between particles was not observed even after calcination at high temperature. The particles prepared at 600°C had amorphous phase, and zinc oxide peaks appeared at 700°C. The peaks of the -Zn2SiO4 with orthorhombic structure was obtained at 1000°C. Pure phase willemite structure was obtained after calcination at 1200°C for 5 h when adding the 80 –90% of stoichiometric amount of zinc nitrate. The maximum cathodoluminescence (CL) intensity of particles was obtained at 1.3 mol% doping concentration of Mn. The particles calcined at 1200°C for 5 h has the maximum CL intensity of 198 cd/m2. © 2000 Elsevier Science Ltd. All rights reserved. Keywords: A. Ceramics; A. Composites; B. Chemical synthesis; D. Luminescence; D. Optical properties
Introduction Various types of multicomponent oxide phosphor particles were widely studied for improved performance in displays and lamps. The mean size of particles is very important factor for high resolution and high efficiency in displays [1,2]. Small particles improve aging
* Corresponding author. Fax: 82-42-869-3910. E-mail address: [email protected] (S.B. Park). 0025-5408/00/$ – see front matter © 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 0 2 5 - 5 4 0 8 ( 0 0 ) 0 0 3 0 6 - 8
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by forming a densely packed phosphor layer. It has been predicted that the optimum phosphor characteristics can be obtained with particle sizes on the order of 1 m. Spherical morphology is also required for high brightness and high resolution of displays. If the phosphor particles have spherical shape, scattering of light emitted from phosphors become diminished. Additionally, spherical phosphor particles are suitable for making high packing density phosphor layer [3,4]. Manganese-doped willemite, Zn2SiO4, is used as green phosphor in fluorescent lamps, cathode ray tubes, and flat panel displays [5–9] Zn2SiO4:Mn particles have been mainly prepared by solid state reactions. In solid-state reactions, it is difficult to prepare phase-pure willemite because of the difference in volatilities of zinc oxide and silicon oxide. In addition, high reaction temperature, long heating time, and milling process are required. Therefore, agglomerated particles with irregular shape and large size are produced by the solid-state reaction method. To overcome the disadvantage of the solid-state reaction method, various liquid solution processes have been introduced for preparing Zn2SiO4:Mn phosphor [7–9]. These liquid solution processes require lower preparation temperatures than that of the solid-state reaction process, but particles of irregular and agglomerated morphology are still produced. Recently, gas phase reaction processes were applied to the preparation of multicomponent phosphor materials. In general, gas phase reactions produce particles of fine size and spherical morphology. Sievers et al. [1] prepared Y2O3:Eu phosphors by CO2-assisted aerosolization. In this technique, supercritical CO2 is combined with aqueous solutions of water-soluble metal nitrates or acetates in a low-dead-volume tee to form emulsions at 10 MPa. Spherical and submicron phosphor particles are formed by rapid desolvation of the aerosol in a tubular furnace by dehydration and pyrolysis. Bihari et al. [10] prepared Y2O3:Eu nanocrystalline phosphors by gas-phase condensation by using CO2 laser heating of ceramic pellets. It should be noted that these gas phase reactions are currently confined to the preparation of phosphors with simple composition. In Kang et al.’s works [11–13], ultrasonic spray pyrolysis, which is one of the gas phase reaction methods, was applied to the preparation of multicomponent phosphor materials. Spray pyrolysis is a method of producing particles, in which a misted stream of precursor solution is dried, precipitated, and decomposed in a tubular furnace reactor. Particles produced by spray pyrolysis are relatively uniform in size and composition because of microscale reaction within a droplet and the lack of milling process. In spray pyrolysis, the rare-earth dopants are well distributed inside host materials, so the produced particles are expected to have good luminescence characteristics compared with other solid or liquid processes. In this study, manganese-doped willemite, Zn2SiO4, phosphor particles were prepared by spray pyrolysis using the FEAG process [14]. Characteristics of particles such as phase purity, crystallinity, mean size, morphology, and cathodoluminescence (CL) were investigated.
2. Experimental The apparatus used in this work was a filter expansion aerosol generator (FEAG), of which details have appeared elsewhere [14,15]. In the FEAG process, the solutions are atomized
Y.C. Kang, S.B. Park / Materials Research Bulletin 35 (2000) 1143–1151
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into droplets of 2 m at 5 ml/min and delivered into a hot-wall reactor at 60 Torr. As the aerosol stream passes through the reactor, the solvent evaporates and the metal salts decompose into individual oxide particles. The reaction of individual particles into single phase multicomponent oxide particles then follows in the high temperature of the reactor. The starting solutions were prepared from zinc nitrate, TEOS (tetraethyl orthosilicate), and manganese acetate. Small amount of nitric acid was added for clear solution. The reaction temperatures were increased from 700 to 1000°C. The as-prepared particles were calcined above 1000°C for crystallization and activation of phosphor materials. To find optimum post-treatment conditions, the particles prepared at 900°C were calcined at each temperatures of 1000, 1100, 1200, and 1300°C. The prepared particles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and centrifugal particle size analysis (CPSA). Cathodoluminescence and chromaticity of the particles were measured by a Minolta CS-100.
3. Results and discussions Fig. 1 shows the SEM photographs of as-prepared and calcined Zn2SiO4:Mn particles. The as-prepared particles at 900°C were calcined at 1000° for 5 h. Both particles had spherical shape, and agglomeration was not apparent even after calcination at high temperature. The mean size of Zn2SiO4:Mn particles prepared from precursor solution of 0.3 M was 1 m. XRD spectra of the particles prepared from the FEAG process was shown in Fig. 2. The particles prepared at 600°C had amorphous phase, and zinc oxide peaks appeared at 700°C. The peaks of the -Zn2SiO4 with orthorhombic structure was obtained at 1000°C. In Fig. 3, XRD spectra of calcined particles were shown. The calcined particles above 800°C for 5 hours had crystalline phase of willemite. The as-prepared particles had poor crystallinity of -Zn2SiO4 and zinc oxide because of the short residence time of particles inside the hot wall reactor. But each component is distributed well inside a particle. Therefore, willemite structure was obtained at lower calcination temperatures than that of solid-state reaction method. On the other hand, ZnO peaks as impurity were shown after calcination below 1000°C. Because of the low boiling point (165°C) of TEOS, some TEOS in droplets evaporated before pyrolysis into SiO2. Due to the volatility of zinc oxide, the XRD intensities of zinc oxide peaks were reduced when the calcination temperature was above 1000°C, and pure phase willemite structure was obtained after calcination at 1200°C for 5 h. The crystallite size of particles calculated from Scherrer’s formula was varied from 290 to 430 nm when the calcination temperature was changed from 900 to 1400°C. The maximum crystallite size was obtained at 1200°C, and the crystallinity of the particles was decreased with increasing the calcination temperature above 1200°C. At high temperatures above 1300°C, the willemite structure destroyed because zinc oxide in the willemite structure evaporated, and the crystallinity of particles decreased. Fig. 4 shows the XRD spectra of particles prepared from different ratios of zinc nitrate and TEOS. The as-prepared particles at 900°C were calcined at 1000°C for 10 h. When adding
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Fig. 1. SEM photographs of as-prepared and calcined particles.
the 80 –90 mol% of the stoichiometric amount of zinc nitrate, pure phase willemite and the highest crystallinity was achieved. Fig. 5 shows the excitation and emission spectra of Zn2SiO4:Mn particles. For the measurement of PL spectra, the as-prepared particles with 1.3 mol% doping of Mn were calcined at 1200°C for 5 h. The particles absorbed excitation energy in the range from 220 nm to 300 nm, and the maximum excitation wavelength was near 253 nm. The main emission peak of particles was 527 nm, resulting in a green emission. The CL intensities of Zn2SiO4:Mn particles were measured when it was excited by field emitter arrays at 400 V and 1 mA/min2 in a high vacuum chamber(10⫺6 Torr). To
Y.C. Kang, S.B. Park / Materials Research Bulletin 35 (2000) 1143–1151
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Fig. 2. XRD spectra of particles at different preparation temperatures. (P600: Preparation temperature ⫽ 600°C).
find the optimum CL intensity, the amount of zinc nitrate in precursor solution was changed from 100 to 60% relative to the stoichiometric amount. The manganese concentration was 1 mol% and the as-prepared particles were calcined at 1000°C for 10 h. In Fig. 6, the CL intensities of Zn2SiO4:Mn particles were varied from 85.9 to 131 cd/m2
Fig. 3. XRD spectra of particles calcined at different temperatures. (C700: Calcination temperature ⫽ 700°C).
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Fig. 4. XRD spectra of particles prepared from different ratios of zinc nitrate and TEOS.
when the amount of zinc nitrate was changed from 100 to 60% relative to the stoichiometric amount. The particles prepared from precursor solution with 80% zinc nitrate relative to the stoichiometric amount had the highest CL intensity. Therefore, the amount of zinc nitrate in precursor solution was fixed at 80% of the stoichiometric amount for the best luminescence of phosphor particles. In Fig. 7, the CL intensities of Zn2SiO4:Mn particles at different manganese concentrations were shown. When the doping concentration of Mn was changed from 0.75 to 2 mol%, the maximum CL intensity was obtained at 1.3 mol% doping concentration of Mn. In Fig. 8, calcination temperature for the crystallization and activation of Zn2SiO4:Mn particles with 1.5 mol% of Mn was changed from 900 to 1300°C to examine its effect on the CL intensity. The particles calcined at 1200°C for 5 h have the maximum CL intensity of 198 cd/m2. This result of CL intensities of particles is well coincided with the results of XRD. In the XRD spectra of particles, the particles calcined at 1200°C had the highest crystallinity of willemite. Generally, particles with large crystallite size have higher brightness than that of particles with small crystallite size, because of low concentration of defects, which act as sites for the nonradiative recombination of electron-hole pairs.
4. Conclusions Mn-doped zinc silicate phosphor particles with spherical shape, nonaggregation, and submicron size were prepared by spray pyrolysis using the FEAG process. Spray pyrolysis had many advantages for the preparation of multicomponent phosphor particles. Rare-earth
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Fig. 5. Excitation and emission spectra of Zn2SiO4:Mn particles.
Fig. 6. CL intensities of particles prepared from different ratios of zinc nitrate and TEOS.
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Fig. 7. CL intensities of particles at different doping concentrations of Mn.
doped multicomponent phosphor particles with pure phase could be prepared at lower temperature than that of the solid-state reaction. The particles were relatively uniform in size and composition because of the microscale reaction within a droplet and the lack of milling process in the spray pyrolysis process. In addition, calcined particles had nonagglomeration at the calcination conditions for optimum brightness.
Fig. 8. CL intensities of particles at different calcination temperatures.
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References [1] R.E. Sievers, P.D. Milewski, C.Y. Xu, B.A. Watkins, Proceedings of Third International Conference on the Science and Technology of Display Phosphors, 1997, p. 303. [2] Y.D. Jiang, Z.L. Wang, F. Zhang, H.P. Paris, C.J. Summers, Proceedings of Third International Conference on the Science and Technology of Display Phosphors, 1997, p. 261. [3] S. Oshio, K. Kitamura, T. Shigeta, S. Horii, T. Matsuoka, T. Kanda, Proceedings of International Display Workshops, 1997, p. 621. [4] S. Oshio, K. Kitamura, T. Shigeta, S. Horii, T. Matsuoka, S. Tanaka, H. Kobayashi, J Electrochem Soc 146 (1) (1999) 392. [5] T. Miyata, T. Minami, K. Saikai, S. Takata, J Lumin 60 – 61 (1994) 926. [6] C. Barthou, J. Benoit, P. Benalloul, A. Morell, J Electrochem Soc 141 (2) (1994) 524. [7] I.F. Chang, J.W. Brownlow, T.I. Sun, J.S. Wilson, J Electochem Soc 136 (11) (1989) 3532. [8] R. Morimo, K. Matae, Mater Res Bull 24 (1989) 175. [9] Q.H. Li, S. Komarneni, R. Roy, J Mater Sci 30 (1996) 2358. [10] B. Bihari, H. Eilers, B.M. Tissue, J Lumin 75 (1997) 1. [11] Y.C. Kang, S.B. Park, I.W. Lenggoro, K. Okuyama, J Phys Chem Solids 60 (3) (1999) 379. [12] Y.C. Kang, I.W. Lenggoro, K. Okuyama, S.B. Park, J Electrochem Soc 146 (3) (1999) 1227. [13] Y.C. Kang, I.W. Lenggoro, S.B. Park, K. Okuyama, J Solid State Chem 146 (1999) 168. [14] Y.C. Kang, S.B. Park, J Aerosol Sci 26 (7) (1995) 1131. [15] Y.C. Kang, S.B. Park, J Mater Sci 31 (1996) 2409.