Combustion synthesized MgAl 2O 4:Cr phosphors—An EPR and optical study

Abstract

Magnesium aluminate (MgAl 2O 4) doped with trivalent chromium (Cr 3+) 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 Cr 3+ ions. The luminescence of Cr 3+-activated MgAl 2O 4 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 2E g→ 4A 2g ground state of Cr 3+ ions. By correlating EPR and optical data the crystal field splitting parameter ( D q), Racah inter-electronic repulsion parameter ( B) and the bonding parameters have been evaluated and discussed. The bonding parameters suggests that the ionic nature of Cr 3+ ions with the ligands and the Cr 3+ ions are in distorted octrahedral environment.