Multicolor tunable bright photoluminescence in Ca2+/Mg2+ modified Eu3+ doped ZnGa2O4 phosphors under UV excitation for solid state lighting applications

Abstract

The Eu³⁺ doped and Mg²⁺/Ca²⁺ co-doped ZnGa₂O₄ phosphor samples were synthesized by solid-state reaction method and their structural and optical properties studied. The phase, crystallinity and particles size of the phosphor samples were studied by XRD and SEM measurements. EDS analyses were used to identify the elements present in the phosphor materials. The vibrational groups present in the phosphor samples were examined by Fourier transform infrared (FTIR) measurements. Pure ZnGa₂O₄ emits intense blue light under 260 nm excitation. However, Eu³⁺ doped and Mg²⁺/Ca²⁺ co-doped ZnGa₂O₄ phosphor samples exhibit intense red emission under 393 nm excitation. A bluish white color is observed in these samples under 290 nm excitation. The maximum PL emission intensity is found at 0.1 mol% Eu³⁺ doping concentration. For higher concentrations, concentration quenching was observed due to dipole–dipole interaction. The emission intensity is enhanced upto 1.20 and 2.91 times on co-doping of Mg²⁺ and Ca²⁺ via induced crystal field due to charge imbalance. The emission intensity of the phosphor is found to enhance further on annealing the samples at 873 K. Under various excitation wavelengths, color tunability was seen from blue to bluish-white to red regions. The lifetime of the ⁵D₀ level of the Eu³⁺ ion improves via doping of Mg²⁺/Ca²⁺ ions and it increases appreciably on annealing. The temperature dependent photoluminescence study (TDPL) reveals a thermal quenching behavior of the sample with thermal stability ∼65% and activation energy ∼0.223 eV in the Eu³⁺/Ca²⁺ co-doped ZnGa₂O₄ phosphor sample.