Jae Seok Lee

Enhanced Luminescence Properties of YAG : Ce3 + Nanophosphor Prepared by Flame Spray Pyrolysis

Cerium-doped Y 3 Al 5 O 12 (YAG):Ce 3+ nanophosphor particles were synthesized using flame spray pyrolysis (FSP) from urea-added nitrate liquid precursor with different molar ratios of yttrium to aluminum. The effect of urea and Y:Al molar ratio in the liquid precursor on the crystallinity and luminescence properties of YAG:Ce 3+ nanophosphors was studied. The cubic YAG structure was obtained after heat-treatment of as-prepared particles. The addition of urea leads to a higher flame temperature and helps in the formation of crystalline phase during FSP. A higher molar concentration of Al in the liquid precursor helped in better incorporation of the dopant atom in the lattice and also promoted the formation of YAG phase. Well-dispersed spherical particles with an estimated size of 50 nm were obtained by the process. The YAG:Ce 3+ nanophosphors synthesized using urea and excess aluminum in liquid precursor showed better crystallinity and higher luminescence intensity.

Synthesis and Characterization of YAG:Ce3+ Nanophosphor prepared by Flame Spray Pyrolysis

Among the various types of synthesis techniques for phosphors, flame spray pyrolysis (FSP) is a powerful method which is capable of producing particles with good crystallinity and high luminescence efficiency. In this work, we have studied the possibility of producing yellow light emitting Ce doped Y3Al5O12 (YAG:Ce) nanophosphor particles using FSP. The challenges in forming YAG arise because of its complex stoichiometry and existence of numerous crystalline states. 3 M of urea was added to increase the flame temperature. The as-prepared nanoparticles were annealed in the temperature range 800°C to 1100°C for 1 hour. As-prepared phosphor particles were found to be YAlO3 which transformed to YAG when annealed above 900°C . PL intensity of the phosphors increased with increase in annealing temperature. These results indicate the possibility of fabrication of high quality YAG:Ce nanophosphor particles via a simple process.

Single-Step Synthesis of Cubic Y2O3:Eu3+ Nanophosphor by Flame Spray Pyrolysis

In this report, we investigated a single-step process for formation of high crystallinity Y2O3:Eu3+ red nanophosphor by flame spray pyrolysis (FSP) without post-heat treatments. Crystallinity of as-formed nanophosphor particle was improved by addition of urea to the nitrate-based liquid precursor. Urea increased the temperature in the flame zone thus ensuring Y2O3:Eu3+ formation at higher flame temperature. Higher temperature reached during combustion of urea promoted the formation of better crystallinity, nano-sized and spherical-shaped particles. The effect of urea in the precursor to obtain high-efficiency Y2O3:Eu3+ nanophosphor was studied.

Solid Phase Crystallization (SPC) of a-Si Thin Film Induced by a Novel Approach for Photovoltaic Devices

The solid phase crystallization (SPC) of amorphous silicon thin films by a novel modification of nucleation step was investigated at low temperature. The thin film consists of polycrystalline nanoparticles embedded in an amorphous matrix which can act as nuclei, resulting in a lower thermal energy for the nucleation. Thus, this energy can shorten the transition time from amorphous to polycrystalline silicon and lower the processing temperature. The crystallinity and the crystallized volume fraction of silicon thin film annealed by the conventional furnace have been extensively studied by XRD and HRTEM. It was believed that high quality Si nanoparticles would act as nuclei for growth of crystalline Si, thus removing the high temperature requirement for nucleation. The crystalline films induced by nanoparticles can be used for the photovoltaic devices on glass substrates at a maximum temperature of 530oC.