An insight into optical spectroscopy of intense green emitting ZnAl2O4:Tb3+ nanoparticles: photo, thermally stimulated luminescence and EPR study

Electron paramagnetic resonance, photoluminescence and thermally stimulated luminescence properties of un-doped ZnAl2O4 and Tb3+ doped ZnAl2O4 phosphors were investigated. The phosphors were synthesized at 1170 K via sol-gel route using the respective metal nitrates and citric acid. The nano-particle nature of the phosphor was confirmed by X-ray diffraction and Scanning Electron Microscope techniques. Time resolved photoluminescence and thermally stimulated luminescence spectroscopic techniques were used to characterize the emission and excitation properties of the system. The decay curve of Tb3+ had shown single exponential behavior with λem=542 and λex=230 nm. TSL glow curve of the ZnAl2O4:Tb3+ nano-phosphor showed a single glow peak at 414 K with heating rate (β)=1 K/s. The trap parameters such as activation energy and frequency factor for the glow peak were determined assuming the Arrhenius behavior for the system. Electron paramagnetic resonance, technique was used to identify the chemical nature of the traps/defects centers responsible for the glow peak. Detailed EPR-TSL correlation study confirmed the destruction of the hole trapped center to be responsible for the observed glow peak. Based on the findings, a probable mechanism was proposed for the glow peak. The emission spectrum of the nano-phosphor was plotted on a standard CIE diagram, which suggested a strong green emission from the phosphor.