INTRODUCTIONPhosphor materials are inorganic materials emitting luminescence in the visible spectral region. Phosphor materials should have narrow size distribution, non-agglomeration and spherical morphology for good luminescent characteristics. Recently, multicomponent oxide particles are studied as phosphor materials for the plat panel display such as FED and PDP(Lee and Yoo, 1996; Morimo et al., 1994). In multicomponent phosphor materials such as titanate, aluminate and silicate, phase purity of particles is very important. In solid state reactions, high reaction temperature, long heating time and milling process are required for phase pure multicomponent particles. Therefore, it is unavoidable to produce agglomerated particles of irregular shapes by solid state reaction. Another disadvantage of the soilid state reaction method is the destruction of phospher materials during the milling process. The physical and chemical damages of surface decrease the brightness of phosphor.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 more uniform in size and composition because of microscale reaction within a droplet and the lack of milling process. Multicomponent materials are also easily prepared by spray pyrolysis, in which droplets of known stoichiometric composition are formed from wide range of precursors soluble to water or organic solvent. Since the particle size and size distribution are determined by the size and size distribution of droplet, selection of spray generator is important to produce uniform and submicron particles.In this study, praseodymium doped calcium titanate particles, one of the phosphor materials, were prepared by spray pyrolysis using filter expansion aerosol generator(FEAG). The characteristics of particles such as photoluminescence, mean size and morphology were investigated.EXPERIMENTAL METHODSExperimental apparatus used in this work was described elsewhere(Kang and Park, 1995). The starting materials was TTIP(Titanium isopropoxide), calcium nitrate and praseodymium nitrate. Titanium hydroxide precipitates was formed when TTIP was added to water at room temperature. The titanium nitrate solution was then formed by adding nitric acid to the titanium hydroxide suspension and stirring for 30 minutes. Calcium nitrate and praseodymium nitrate were dissolved in the titanium nitrate solution with Ca/Ti molar ratio 1:1. The amount of praseodymium changed from 0.1 mol% to 1 mol% for the maximum photoluminescence. Solution concentration was increased from 0.08 mol/l to 1 mol/l, and the mean size and size distribution were measured. The reaction temperatures were increased from 700 °C to 1000 °C. The prepared particles were calcined above 1000 °C for activation of phosphor materials. To find optimum calcination conditions, the particles prepared at 900 °C were post-treated at temperatures between 1000 °C to 1300 °C, and calcination time was 3, 5 and 7 hours.The prepared particles were characterized with X-ray diffractometry(XRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM), and centrifugal particle size analyzer(CPSA, SP-CP3, Schimadzu). Photoluminescence and chromaticity of the particles were measured by Minolta CS-100.RESULTS AND DISCUSSIONFrom the XRD spectra, the particles prepared at 800 °C are amorphous because of low temperature and short residence time as 0.01 sec. But the particles prepared at 900 °C have crystalline phase with sharp peaks of perovskite. The prepared particles had spherical morphology, and the mean size was increased from 0.90 to 1.68μm as the overall solution concentration was increased from 0.08 to 1.1μm. Fig. 1 shows the SEM photograph of calcium titanate particles when the overall solution concentration was 1.1 mol/l. The particles calcined at 1000 °C for 5 hr had also spherical morphology, and agglomeration of particles was not serious. The mean size of calcined particles was 2.6 μm.Comparing the brightness of various praseodymium concentration, the particles with 0.4 mol% praseodymium had the highest brightness. Fig. 2 is the PL(photoluminescence) spectra of particles calcined at 1200 °C for 3 hr with 0.4 mol% praseodymium. The excitation wavelength was near 329.5 nm, and the emission wavelength was near 615 nm. The PL of the particles annealed at 1200 °C for 5hr was 22.2 cd/m 2 . In order to compare the effectiveness of the current aerosol method with the solid-state reaction method, a serious of particles were prepared by a solid state reaction method. The maximum brightness was obtained from particles annealed at 1200 °C for 12 hr. But the PL of these particles was only 11 cd/m 2 .