Combustion synthesized MgAl2O4:Cr phosphors-An EPR and optical study

Magnesium aluminate (MgAl2O4) doped with trivalent chromium (Cr3+) was synthesized by the combustion method. The prepared sample was characterized by X-ray powder diffraction, Brunauer-Emmet-Teller (BET) adsorption isotherms and diffuse-reflectance UV-vis spectroscopy techniques. Electron paramagnetic resonance (EPR) and photoluminescence (PL) studies have been performed at room temperature and at 110 K. The EPR spectrum exhibit resonance signals at g=5.37, 4.53, 3.82, 2.26 and 1.96 characteristic of Cr3+ ions. The luminescence of Cr3+-activated MgAl2O4 exhibits a red emission peak around 686 nm from the synthesized phosphor particles upon 551 nm excitation. The luminescence is assigned to a transition from the upper 2Eg→4A2g ground state of Cr3+ ions. By correlating EPR and optical data the crystal field splitting parameter (Dq), Racah inter-electronic repulsion parameter (B) and the bonding parameters have been evaluated and discussed. The bonding parameters suggests that the ionic nature of Cr3+ ions with the ligands and the Cr3+ ions are in distorted octrahedral environment.