Characterization, EPR and photoluminescence studies of LiAl5O8:Cr phosphors

Red emitting Cr3+ doped LiAl5O8 powder phosphor was prepared by combustion route using corresponding metal nitrates and urea in a single step. The prepared powder was characterized by X-ray diffraction and surface area measurements were carried out by Brunauer–Emmet–Teller adsorption isotherms. The electron paramagnetic resonance spectrum in the low field regions is typical for isolated Cr3+ ions whereas the resonance signal in the high field region with g = 1.95 is due to exchange coupled Cr3+–Cr3+ pairs. The optical studies show two broad and intense bands characteristic of Cr3+ ions in distorted octahedral symmetry. The photoluminescence spectrum gives a narrow red emission at 710 nm corresponding to 2Eg → 4A2g transition upon excitation of 562 nm. The crystal field parameter (Dq), Racah inter-electronic repulsion parameters (B and C) and nephelauxetic parameters have been evaluated and discussed.