Hyun Sook Roh

Synthesis of Nanosize Gd2 O 3 : Eu Phosphor Particles with High Luminescence Efficiency under Ultraviolet Light

To synthesize nanosize Gd 2 O 3 :Eu phosphor particles with high luminescence efficiency under UV light, organic additives such as citric acid and ethylene glycol and N2 a CO 3 , flux were introduced in large-scale spray pyrolysis. Gd 2 O 3 :Eu phosphor particles prepared from solution with polymeric precursors such as citric acid and ethylene glycol had micrometer size and spherical shape. However, particles prepared from polymeric precursor solution with Na 2 CO 3 flux were nanosize and had nonaggregation characteristics. The as-prepared spherical particles with micrometer size turned into nanosized particles during post-treatment by recrystallization process. The nanosized Gd 2 O 3 :Eu phosphor particles showed high brightness under 254 nm UV light. The photoluminescence (PL) intensity of the particles prepared from polymeric precursor solution with Na 2 CO 3 flux material and post-treated at 1050°C, which are nanosize and have nonaggregation characteristics, was identical to 109% of that of the Y 2 O 3 : Eu commercial product. The particles post-treated at 1150°C had a PL intensity 34% higher than the commercial product while showing aggregated characteristics.

Morphology of Oxide Phosphor Particles Prepared by Colloidal Seed‐Assisted Spray Pyrolysis

Gd 2 O 3 :Eu phosphor particles of spherical and filled morphology were prepared by spray pyrolysis. Morphology control of Gd 2 O 3 :Eu phosphor particles in spray pyrolysis was attempted by using colloidal and aqueous solutions. The particles prepared from colloidal solutions containing small amounts of gadolinium hydroxy carbonate sol as seed material had a filled morphology before and after the post treatment; whereas the particles prepared from aqueous solutions were hollow and the structure was broken after post treatment at 1200°C. The particles prepared from colloidal seed solution with 250 nm sol had a spherical and filled morphology with a clean surface; the particles prepared from colloidal seed solution with 70 nm sol had a collapsed spherical shape. The particles prepared from colloidal and aqueous solutions had similar photoluminescent intensities.

Vacuum ultraviolet characteristics of nano-sized Gd2O3:Eu phosphor particles

Nano-sized Gd2O3:Eu phosphor particles having a high photoluminescence efficiency under vacuum ultraviolet (VUV) light were prepared by ultrasonic spray pyrolysis. The introduction of organic additives such as citric acid and ethylene glycol and Na2CO3 flux material in a large-scale spray pryolysis enabled the formation of Gd2O3:Eu phosphor particles with nano-size, spherical-like shape, clean surface, and non-aggregation characteristics even at high solution concentration as 1 M. To enhance the photoluminescene (PL) intensities of nano-sized Gd2O3:Eu phosphor particles under VUV light of 147 nm wavelength, the doping concentration of Eu, addition amounts of polymeric precursors and Na2CO3 flux, and posttreatment temperature were optimized. The nano-sized Gd2-xO3:Eux (x=0.1) phosphor particles prepared from solution containing 3 wt.% Na2CO3, 0.2 M citric acid and 0.2 M ethylene glycol and posttreated at 1150°C for 3 h showed the maximum PL intensity, which corresponded to 115% that of the commercial Y2O3:Eu product.

Morphological control of Zn2SiO4:Mn phosphor particles by adding citric acid in spray pyrolysis process

Zn2SiO4:Mn phosphors for plasma display panels (PDP) application were synthesized by large-scale ultrasonic spray pyrolysis process using metal alkoxide precursor. To avoid the formation of irregular-shaped particles owing to the hollowness and phase-segregation characteristics of the silicon component, organic additive, citric acid (CA) was introduced in the spray pyrolysis. The influence of CA addition on the morphological and luminescent characteristics of the Zn2SiO4:Mn phosphor particles was investigated. The amount of CA addition is an important factor in controlling the morphological and luminous characteristics of Zn2SiO4:Mn phosphor particles. The particles prepared from the solution containing an appropriate amount of CA had a completely spherical shape, dense morphology, nonaggregation characteristics, and higher photoluminescence intensity than the commercial product, while those prepared from the solution containing excessive CA had an irregular shape, high porosity, rough surfaces, and lower brightness than the commercial product.

High luminescence Y2O3 : Eu phosphor particles prepared by modified spray pyrolysis

Highly efficient phosphor material with a well-crystallized micron size, spherical morphology, and nonaggregation characteristics is a desired requirement for flat panel displays and lamps [1–5]. Phosphor particles are mainly prepared by conventional solid-state reaction or liquid solution methods. The characteristics of phosphor materials are highly affected by preparation method. The conventional processes have disadvantages in that the are difficulties in controlling the morphology and maintaining the uniformity in composition of phosphor particles [6–8]. Spray pyrolysis is a feasible process for the preparation of improved phosphor particles.The phosphor particles prepared by spray pyrolysis almost satisfy the requirements of phosphor particles for flat panel displays [9]. But a disadvantage of spray pyrolysis in some case is the lack of morphological control over the product particles and the subsequent frequent formation of hollow and/or porous particles. The hollowness of particles can cause a reduction in brightness and long-term stability of phosphor particles. Therefore, morphology control of phosphor particles in the spray pyrolysis is crucial. In spray pyrolysis, high-solubility precursors, low evaporation rates, small droplet sizes, low solution concentrations, and long residence times promote solid particle formation [10]. Morphological control of particles in spray pyrolysis can also be carried out by using stable colloidal seed solution prepared by liquidphase reaction method [11]. Flame spray pyrolysis is another method for producing solid particles, where the high-temperature flame used as an energy source causes melting as the particle to be spherical and dense [12]. In conventional solid-state reaction and liquid solution methods, flux materials are inevitably used to promote crystal growth and improve the brightness of phosphor particles. To improve the luminescence characteristics of phosphor particles, flux material was also introduced in the preparation of phosphor particles by spray pyrolysis. The phosphor particles pre-

Red-Emitting Phosphor Particles with Spherical Shape, Dense Morphology, and High Luminescent Efficiency under Ultraviolet

Gd2O3:Eu phosphor particles of spherical shape, filled morphology, and high brightness were prepared by large-scale spray pyrolysis. The morphology control of Gd2O3:Eu particles was attempted by adding organic precursors in a spray solution. The influence of chain length of organic additives and introduction of esterification reaction within the droplet on the morphological and luminescent characteristics of Gd2O3:Eu particles was studied. The particles prepared from aqueous solution with no organic additive showed the hollow and porous shell structure and poor brightness, while those particles prepared from solutions with only polyethylene glycol (PEG) exhibited relatively filled structure and high brightness. The longer the chain length of added PEG is, the better morphological and luminescence characteristics the particles showed. The introduction of esterification reaction within the droplet by adding citric acid (CA) and ethylene glycol (EG) or PEG with various molecular weight enhanced the morphological characteristics and significantly improved photoluminescence characteristics regardless of chain length of PEG. The particles prepared from solution containing 0.1 M CA and 0.1 M PEG (M.W. 1500) showed the maximum photoluminescence intensity, which was 148% that of commercial product.

Improvement of Brightness of Gd2O3:Eu Phosphor Particles Using Boric Acid Flux in the Spray Pyrolysis

Gd2O3:Eu phosphor particles of high brightness were directly prepared by the spray pyrolysis from solution with boric acid flux. The particles prepared from solutions with boric acid flux had higher photoluminescence (PL) intensities than that of particles prepared from solution without flux. The particles prepared from the solution of 10 wt% boric acid had the highest PL intensity, which was higher by 43% than that of the particles prepared from solution without flux. The roles of boric acid flux in improving PL intensity of Gd2O3:Eu phosphor particles in the spray pyrolysis were to promote crystal growth and to reduce surface defect of particles. They were different from ones in solid state reaction.

ZnGa2O4:Mn Phosphor Particles with Spherical Shape and Clean Surface

ZnGa2O4:Mn phosphor particles of spherical shape, clean surface, filled morphology, and improved photoluminescence characteristics were prepared by a modified spray pyrolysis technique and the effect of precursor type on the luminescence intensity of ZnGa2O4:Mn was investigated. The morphology control of ZnGa2O4:Mn phosphor particles in spray pyrolysis was attempted by using the stable colloidal solution obtained by the liquid phase reaction method as a spraying solution. The ZnGa2O4:Mn particles prepared from the colloidal solution had a spherical shape, clean surface, and filled morphology even after post-treatment at 1200°C. The ZnGa2O4:Mn particles prepared from Zn chloride and Mn acetate showed the maximum photoluminescence intensity, which was 24% higher than that of particles prepared from Zn nitrate and Mn nitrate.