Microstructure, phase transformation and photoluminescence of YAG:Ce ceramics by CO2 laser sintering

Abstract

This study applied laser sintering to transform yttria, alumina, and cerium nitrate powders into Y3Al5O12:Ce (YAG:Ce) phosphor layers. Different hatch distances (0.3 mm–0.7 mm) were performed on the precursors to evaluate their reaction area, depth, and affected zone. Microscopic images and x-ray diffraction results indicated that a hatch distance corresponding to the laser spot size (0.5 mm) is the critical distance between laser scan vectors so as to avoid the residual precursors. Moreover, the grains in YAG:Ce layers presented a texture structure of columns, which are identical to the heat flows during laser sintering. Transmission electron microscopy revealed amorphous boundaries surrounded YAG:Ce single crystals. Photoluminescence of laser-sintered YAG:Ce (0.3 mm hatch distance) by blue excitation was enhanced by around 40% as compared to the solid state reacted one, which should result from rougher surfaces as well as the presence of amorphous boundaries for better light penetration and propagation.