A study on the optimal luminescence properties and thermoluminescence characteristics of ZnAl2O4:Eu3+nanophosphor for solid-state lighting and dosimetric applications

This study examines the photoluminescence and thermoluminescence properties of Eu3+ doped (0.3-3 mol%) ZnAl2O4 nanocrystals, prepared via microwave combustion method using piper-nigrum seeds extract as reducing agent followed by the annealing at 900 degrees C for 1.5 h. The XRD and Rietveld analysis confirms cubic spinel nanocrystals (14 nm-18 nm), where Eu3+ replaces Zn2+ ions at tetrahedral sites. The charge transfer bands associated to Eu-O are displayed in the diffuse reflectance spectra of all the samples. The direct optical energy band gap determined by K-M function was found to decrease from 3.26 eV to 3.18 eV with increasing dopant concentration. Upon excitation at 394 nm, ZnAl2O4 emits red light (616 nm) with the dominant 5D0 -> 7F2 transition. With CIE colour coordinates of x = 0.5874, y = 0.4100, correlated colour temperature of 1574 K, colour rendering index of 73, red colour purity of 97.5 %, and quantum efficiency of 62 %, the ZnAl2O4:Eu3+ (1mol%) sample exhibits exceptional luminescence performance. The PL concentration quenching and radiative transition probability is discussed by crystal field symmetry and Judd-Ofelt (J-O) theory. The high radiative transition probability, high external quantum efficiency, high covalency, low symmetric environment around the Eu3+ ions are some important conclusions from the analysis of J-O parameters. From the thermoluminescence kinetics, TL glow curves show peaks at 416 K and 577 K, with activation energies between 0.63 eV and 1.12 eV. The kinetics and other parameters were evaluated by computerized glow curve deconvolution method. The linear TL dose response establishes its potential as a gamma-radiation dosimeter, making the ZnAl2O4 nanophosphor suitable radiation dosimetry applications. Furthermore, highly efficient sharp red emission shows its potential for solid-state lighting.