Study of crystallization kinetics, microstructure and optical properties of Ce: YAG glass-ceramics for white LED applications

Abstract

CeO2 doped Y2O3-Al2O3-SiO2 (YAS) glass composition was synthesized and devitrified to a single phase Ce: YAG glass–ceramics phosphor with controlled heat treatment process. Kinetic predictions for crystallization of the glass were derived from isoconversional analysis of DTA data using AKTS software. Activation energy of crystallization (E) at reaction progress (α = 0.5) estimated 659 kJ mol−1. The kinetic parameters were calculated as n = m = 2, representing two-dimensional nucleation and crystal growth with constant number of surface nuclei in this glass composition. From microstructure analysis of glass–ceramics we have seen the dendritic growth of crystals in the glass matrix originating from the surface creating a glass–ceramics phosphor layer of ~ 50 μm thick. No nucleation or crystal growth observed in the glass beyond 50 μm depth. Surface roughness found to increase the nucleation and accelerate the crystallization in the glass–ceramics layer. Five glass–ceramics samples prepared with increasing isothermal holding time and their photoluminescence spectra obtained by excitation with a blue LED light source. Intensity of broad band yellow emission increased with the increase in holding time which enhances the amount of Ce: YAG crystalline phase in glass–ceramics. A device was assembled for the demonstration of white light generation using an optimized glass–ceramics phosphor and blue LED in tandem.