Electron paramagnetic resonance and luminescence study of sol-gel derived YAG : Cr powder

Abstract

Electron paramagnetic resonance (EPR) and luminescence studies were carried out for the sol-gel-derived YAG:Cr powders subjected to three kinds of heat treatment processes. The results show that powders processed using the two-step heat treatment process with the addition of 20 wt% LiCl and by direct heat treatment at 1500 degrees C exhibit good luminescence properties. The emission spectrum for the powders obtained by the two-step process shows the R-line at 688 nm, whereas the powders directly heat treated at 1500 degrees C display an additional R-line of Al2O3 : Cr at 694 nm: EPR measurements show that the presence or absence of absorption peaks depends on the Cr3+ environment in-the host lattice resulting from the different methods of heat treatment of the powder. The EPR spectra of YAG:Cr3+ phosphors were interpreted to indicate both Cr3+ single ion and Cr3+-Cr3+ pair (with spin three) transitions.