Color tunability and NIR luminescence in Cr3+/Li+ co-doped ZnGa2O4 phosphor for solid state lighting and NIR LEDs

Abstract In this work, we report the color tunable photoluminescence in the Cr 3+ /Li + doped and co-doped ZnGa 2 O 4 (ZGO) phosphors synthesized by solid state reaction method. The phase and surface morphology of ZGO phosphor were examined by XRD and SEM measurements, respectively. The EDS spectra revealed the presence of Zn, Ga, Cr and O elements in the phosphor. The vibrational structure of the phosphor materials has been analyzed by FTIR measurements. The Cr 3+ doped phosphor shows electronic absorption bands at 302, 408 and 544 nm alongwith the host CTB at 260 nm. The optical band gap of the phosphor decreases via doping of Cr 3+ and Cr 3+ /Li + ions. The ZGO is a self-activated host and emits broad blue emission with maximum at 434 nm upon excitation at 260 nm. The Cr 3+ doped phosphors show emission bands due to spin-allowed as well as spin-forbidden transitions due to Cr 3+ ion in the blue, green and NIR regions on excitation with 260, 302, 408 and 544 nm wavelengths. The emission intensity is optimum for 0.5 mol% concentration of Cr 3+ ion. The emission intensity of Cr 3+ doped ZGO phosphor increases via doping of Li + ion. The color tunability has been observed in the phosphor upon 260 and 302 nm excitations. The lifetimes of 4 T 2 ( 4 F) and 2 E states of Cr 3+ ion have been measured and it is found that it decreases with increasing concentrations of Cr 3+ and Cr 3+ /Li + ions. The Cr 3+ /Li + doped and co-doped ZGO phosphors may be suitable candidates for display devices, solid state lighting and NIR LEDs.