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

Electron paramagnetic resonance (EPR) and luminescence studies were carried out for the sol-gel-derived YAG:Cr powders subjected to three kinds of hea t treatment processes. The results show that powders processed using the tw o-step heat treatment process with the addition of 20 wt% LiCl and by direc t heat treatment at 1500 degrees C exhibit good luminescence properties. Th e 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 deg rees C display an additional R-line of Al2O3 : Cr at 694 nm: EPR measuremen ts show that the presence or absence of absorption peaks depends on the Cr3 + environment in-the host lattice resulting from the different methods of h eat treatment of the powder. The EPR spectra of YAG:Cr3+ phosphors were int erpreted to indicate both Cr3+ single ion and Cr3+-Cr3+ pair (with spin thr ee) transitions.