Seung Kwon Hong

Luminescence Characteristics of Eu-Doped Calcium Magnesium Chlorosilicate Phosphor Particles Prepared by Spray Pyrolysis

Europium (Eu)-doped calcium magnesium chlorosilicate [Ca8Mg(SiO4)4Cl2:Eu2+] phosphor particles were prepared by spray pyrolysis and their luminescence characteristics were optimized by changing the Ca precursor type, the Eu2+ content, and the post-treatment temperature. It was found that the ratio of calcium nitrate to calcium chloride, which were used as the source of Ca and Cl, respectively, significantly affects the luminescence intensity and the particle morphology. Photoluminescence intensity was monotonically increased by increasing calcium chloride content with respect to calcium nitrate content in the spray solution due to increases in the crystallinity and phase purity of Ca8Mg(SiO4)4Cl2:Eu2+. Ca8Mg(SiO4)4Cl2:Eu2+ was gradually turned from a spherical shape to a polyhedral shape of micron size as the calcium chloride content was increased in the spray solution. The concentration quenching of Eu2+ was observed at 0.375 mol % Ca. The optimized Ca8Mg(SiO4)4Cl2:Eu2+, which showed a broad emission spectrum from 460 to 550 nm with a peak position at 502 nm, had a high brightness under the excitation by short- and long-wavelength ultraviolet lights and is expected to be successfully applied as a green phosphor for UV light emitting diodes (LEDs).

Morphology Control of Gd2O3:Eu Phosphor Particles with Cubic and Monoclinic Phases Prepared by High-Temperature Spray Pyrolysis

Gd2O3:Eu phosphor particles with cubic and monoclinic phases were directly prepared by high-temperature spray pyrolysis from aqueous, polymeric precursor and colloidal solutions. The colloidal solution with nanosized silica was effective for the preparation of Gd2O3:Eu phosphor particles with a cubic phase, a high photoluminescence intensity and a good morphology. The phosphor particles prepared from colloidal solutions with nanosized silica obtained by hydrolysis had a small size, a narrow size distribution, a spherical shape and a filled morphology. The optimum doping concentration of nanosized silica particles was 0.5 wt % of the product particles. The phosphor particles prepared by spray pyrolysis from colloidal solutions at temperatures below 1580 °C had the photoluminescence spectrra of the cubic phase and a maximum photoluminescence intensity at a temperature of 1560 °C.

Effect of boric acid flux and drying control chemical additive on the characteristics of Y2O3:Eu phosphor particles prepared by spray pyrolysis

Y2O3:Eu phosphor particles with a spherical shape, a fine size, and high brightness under vacuum ultraviolet (VUV) illumination were prepared by spray pyrolysis. The polymeric precursors were needed to modify the spray solution to prepare spherical particles. The use of only flux with the polymeric precursors did not produce dense and spherical Y2O3:Eu particles; that is, the produced particles were very porous. The addition of both a drying control chemical additive (DCCA) and boric acid to a spray solution containing polymeric precursors was found to produce Y2O3:Eu phosphor particles with a dense structure while maintaining the spherical morphology. According to X-ray diffraction (XRD) analysis, the DCCA induced an enhancement of crystallinity. The use of boric acid flux improved the photoluminescence (PL) intensity under VUV illumination. In addition, the use of both boric acid flux and a DCCA with polymeric precursors further improved the PL intensity owing to the enhancement of the morphology and the crystallinity.

CeTb)MgAl11O19 phosphor particles prepared by spray pyrolysis from spray solution containing citric acid and ethylene glycol

(CeTb)MgAl11O19 (CTMA) phosphor particles were prepared by spray pyrolysis from polymeric precursor solutions under severe preparation conditions. Citric acid and ethylene glycol used as polymeric precursors formed as-prepared and post-treated (CeTb)MgAl11O19 phosphor particles with a spherical shape and a dense morphology. The CTMA phosphor particles prepared from polymeric precursor solutions at 1600°C had a completely spherical shape, a dense morphology, and a nonaggregated morphology after post-treatment at 1400°C. The CTMA phosphor particles prepared from the polymeric precursor solution had a lower impurity content than those prepared from a pure aqueous solution. All the phosphor particles prepared from the polymeric precursor solution had higher photoluminescence intensities than those prepared from the pure aqueous solution at all temperatures. The photoluminescence intensity of the CTMA phosphor particles prepared from the polymeric precursor solution was 108% that of the phosphor particles prepared from the pure aqueous solution at 1600°C.

Direct Synthesis of High-Brightness (CeTb)MgAl11O19 Phosphor Particles by Spray Pyrolysis with Boric Acid Flux

High-brightness (CeTb)MgAl11O19 (CTMA) phosphor particles were directly prepared by high temperature spray pyrolysis. The boric acid flux added into spray solution affected the morphology and photoluminescence intensity of the CTMA phosphor. The phosphor particles prepared from spray solution with 20 wt % boric acid of the product had a spherical shape and a filled morphology at 1600°C. The phosphor particles prepared by spray pyrolysis from spray solution without flux material under reducing atmosphere at 1600°C had high photoluminescence intensities under ultraviolet. The boric acid flux improved the photoluminescence intensities of the CTMA phosphor. The maximum photoluminescence intensity of the phosphor particles prepared from spray solution with an optimum amount of added boric acid flux was 114% of that of the phosphor particles prepared from spray solution without flux material. The particles directly prepared by spray pyrolysis from spray solution with 20 wt % boric acid of the product had a pure crystal structure of the CTMA phosphor.

Effects of Y/Gd Ratio and Boron Excess on Vacuum Ultraviolet Characteristics and Morphology of (Y,Gd)BO3:Eu Phosphor Particles Prepared by Spray Pyrolysis

(Y1-xGdx)BO3:Eu (0≤x≤1) phosphor particles were prepared by spray pyrolysis. The optimal amount of boric acid for the high photoluminescence intensity of there particles differed depending on the molar ratio of Y to Gd. With decreasing Y/Gd molar ratio, an increasing amount of excess boric acid was required. The difference in excess quantity of boric acid, which was demanded for the highest photoluminescence intensity according to the Y/Gd ratio, influenced the morphology and mean size of the (Y,Gd)BO3:Eu phosphor particles. The (Y1-xGdx)BO3:Eu (0≤x≤1) phosphor particles had a regular morphology. The mean sizes of the GdBO3:Eu and YBO3:Eu phosphor particles were 1.4 and 1 µm, respectively. The high reactivity of boron and yttrium components produced YBO3:Eu phosphor particles with high photoluminescence intensities by spray pyrolysis using a spray solution with a stoichiometric amount of boric acid.

Characteristics of TAG:Ce Phosphor Particles Prepared by Ultrasonic Spray Pyrolysis

Tb3Al5O12:Ce (TAG:Ce) phosphor particles were prepared by spray pyrolysis process. The TAG:Ce phosphor particles prepared by spray pyrolysis had good characteristics such as fine size, narrow size distribution, and high photoluminescence intensity under blue light excitation. The TAG:Ce phosphor particles had the maximum photoluminescence intensity after post-treatment at 1550oC under reducing atmosphere. The photoluminescence intensity of the prepared TAG:Ce phosphor particles was 85% of the optimized YAG:Ce phosphor particles.

Characteristics of Fe powders prepared by spray pyrolysis from a spray solution with ethylene glycol as the source material of heat pellet

Fe powders as the heat pellet material for thermal batteries are prepared from iron oxide powders obtained by spray pyrolysis from a spray solution of iron nitrate with ethylene glycol. The iron oxide powders with hollow and thin wall structure produce Fe powders with elongated structure and fine primary particle size at a low reducing temperature of 615 °C. The mean size of the primary Fe powders with elongated structure decreases with increasing concentration of ethylene glycol dissolved into the spray solution. The heat pellets prepared from the fine-size Fe powders with elongated structure have good ignition sensitivities below 1 watt. The heat pellets formed from the Fe powders obtained from the spray solution with 0.5 M EG have an extremely high burn rate of 26 cms−1.

The Characteristics of Fine-Sized LiMn(12-X)/6Alx/6O4(0.05≤x≤2) Powders Prepared by Spray Pyrolysis

The series of partially Al-substituted lithium manganese oxides were prepared by spray pyrolysis process from spray solutions with citric acid and ethylene glycol. The as-prepared particles obtained from spray solution with citric acid and ethylene glycol turned to fine-sized LiMn(12- x)/6Alx/6O4(0.05≤x≤2) particles with regular morphology after post-annealing. The discharge capacities of the particles post-annealed at temperature of 800oC changed from 128 to 84 mAh/g when the x of the LiMn(12-x)/6Alx/6O4 particles was changed from 0 to 2. The Al-doped LiMn2O4 fine particles prepared by spray pyrolysis from spray solution with citric acid and ethylene glycol had good cycle properties.

Effect of preparation temperature on the formation of Sr2CeO4 phosphor particles in the spray pyrolysis

Sr2CeO4 phosphor particles were prepared by spray pyrolysis at various preparation temperatures. The effect of preparation temperatures on the morphology, crystal structure and photoluminescence characteristics of the post-treated Sr2CeO4 phosphor particles was studied. Phase pure Sr2CeO4 phosphor particles were not produced by spray pyrolysis without post-treatment. The optimum post-treatment temperature to produce the Sr2CeO4 phosphor particles with high photoluminescence intensity was 1,000 °C in spray pyrolysis. The spherical morphology of the as-prepared particles obtained at high preparation temperatures above 1,400 °C had maintained after post-treatment at 1,000 ‡C. The relative photoluminescence intensities of the Sr2CeO4 phosphor particles varied with the preparation temperatures in the spray pyrolysis. The as-prepared particles obtained by spray pyrolysis at preparation temperatures below 1,400 °C converted into phase pure Sr2CeO4 phosphor particles after post-treatment at 1,000 ‡C. The optimum preparation temperature of the as-prepared particles was 1,400 °C to produce the Sr2CeO4 phosphor particles with spherical shape and high photoluminescence intensity in the spray pyrolysis.