Papers by Author: Sung Hoon Lee

Abstract: Spray pyrolysis was used to prepare ZnS:Mn2+ yellow nanophosphor. As an increase in firing temperature for spray pyrolysis, more nanoparticles of a hexagonal phase were formed together with these of the cubic structure. The optimized emission intensity was observed when the nanophosphor was fired at 900 oC after using a spraying solution of 3.5 pH. The particle size ranged from 60 nm to 400 nm. The ZnS:Mn2+ nanophosphor showed a redshift of about 10 nm in the emission spectrum compared to the microphosphor synthesized by solid-state reaction. The temperature-dependence photoluminescence showed different spectroscopic behaviour and displayed a longer decay time than the microphosphor.

Abstract: Manganese-doped ZnS nanophosphors were synthesized by two different methods: hydrothermal and low-temperature precipitation methods. The nanophosphors prepared by the hydrothermal precipitation and low-temperature methods had the size of 20 nm and 4 nm, respectively, and both were the cubic phase. The emission intensity of the nanophosphor prepared by the hydrothermal method was optimized at 10 mole % of Mn2+ concentration whereas that by low-temperature precipitation method was optimized at 3 mole % of Mn2+. The precipitationprepared nanophosphor, of size 4nm, showed a blueshift in the excitation spectrum and a redshift in the emission spectrum compared to the hydrothermal-prepared 20 nm nanophosphor. These phenomena can be explained in terms of the quantum confinement effect. The decay times especially were lengthened with decreasing particle size. This can be explained in terms of the variation in the transition probability induced from the quantum confinement effect.