Combustion synthesized MgAl(2)O(4):Cr phosphors-An EPR and optical study

Magnesium aluminate (MgAl(2)O(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(2)O(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 (2)E(g)-->(4)A(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. (C) 2008 Elsevier B.V. All rights reserved