Controlling disorder in the ZnGa sub(2)O sub(4):Cr sup(3+) persistent phosphor by Mg sup(2+) substitution

Abstract

In this work we study the effect of increasing site occupancy disorder on the persistent luminescence of Cr sup(3+) doped zinc gallate spinel. This disorder was introduced by progressive substitution of Zn sup(2+) by Mg sup(2+) ions, and was studied by photoluminescence, x-ray diffraction, extended x-ray absorption fine structure (EXAFS), x-ray absorption near edge structure (XANES) and electron paramagnetic resonance (EPR) spectroscopy. It was found that increasing Mg/Zn ratio decreases the number of Cr sup(3+) in undistorted octahedral sites, increases the number of Cr sup(3+) with neighbouring antisite defects and also increases Cr sup(3+) ions with Cr - O - Cr linkages (referred as Cr clusters), which is responsible for the decrease in the intensity of persistent luminescence. Both XANES and EPR spectra could be simulated by a linear combination of Cr sup(3+) spectra with above three types of Cr sup(3+) environments. The increasing site occupancy disorder and formation of Cr clusters was found to be correlated with the decreasing lattice parameter of the host lattice