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 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°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°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.