Electron Paramagnetic Resonance and Photoluminescence Studies of Ultraviolet-Emitting ZnAl2O4:Gd3+ Phosphors

Gadolinium-doped ZnAl2O4 ultraviolet-emitting powder phosphor was prepared at ∼773 K within a few minutes by the combustion route. A cubic spinel structure of the as-prepared sample was confirmed by the x-ray diffraction method. The morphology and homogeneity of chemical composition of the sample were analyzed using scanning electron microscopy and energy-dispersive x-ray analysis, respectively. Electron paramagnetic resonance (EPR) and photoluminescence studies were performed on the Gd-doped ZnAl2O4 phosphors. The EPR spectrum exhibited signals with effective g values at g = 5.7, 4.4, 3.4, 2.8, 2.3, and 2.0. The signals with effective g values at g = 5.7, 2.8, and 2.0 are attributed to strong, intermediate, and weak cubic crystal fields. The signal at g = 4.4 is attributed to a strong crystal field with orthorhombic symmetry. The signals at g = 3.4 and 2.3 are attributed to the vitreous structure. The emission spectrum exhibits an intense band in the ultraviolet (UV) region centered at 312 nm (32,051 cm−1), being assigned to the 6P7/2 → 8S7/2 transition.