The structure and photoluminescence performances of ZnxAl2O4:Cr3+ crystals with various annealing temperatures

ZnxAl2O4: Cr3+ (0.1 mol%) crystals were synthesized by using sol-gel method follow by the annealing treatment with temperatures ranging from 600 degrees C to 1000 degrees C. A series of emission peaks associated with the spin-forbidden E-2(g)->(4)A(2g) transition of Cr3+ ions were observed at the range from 650 nm to 720 nm. With the Zn/Al molar ratio increasing, the results of X-ray photoelectron spectra showed that the excess Al ions occupying tetrahedral sites decreased. Meanwhile the full width at half maximum of emission peaks became much narrower, and the intensity ratio between R line and N line increased for all samples but decreased with the annealing temperature increasing.