Enhanced luminescence of ZnO:RE3+ (RE=Eu, Tb) nanorods by Li+ doping and calculations of kinetic parameters

Lithium co-doped ZnO:Eu3+ and ZnO:Tb3+ nanophosphors were prepared by co-precipitation method and the effect of Li+ co-doping was systematically studied by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), UV-Vis-NIR reflectance, Photoluminescence (PL) spectroscopy and Thermoluminescence (TL) studies. XRD pattern shows typical peak pattern for hexagonal wurtzite structure and matches JCPDS card no. 79-0206. A shift of the (1 0 1) peak towards the lower angle in Li+ co-doped samples can be observed showing the increase of lattice constant for the incorporation of Li+ ions in the lattice sites. The present samples are found to be consisting of nanorods of diameter 60-90 nm as revealed by the SEM image. The FTIR pattern shows the enhancement of peak intensity for the ZnO in the Li+ co-doped samples. The diffuse reflectance study shows red shift of the absorption edges in Li+ co-doped ZnO:Eu3+ and Li+ co-doped ZnO:Tb3+. PL study reveals that a very small amount of Li+ is very effective for charge compensation and for producing lattice defect to enhance the rare-earth related emissions, whereas a little excess of Li+ brings oxygen vacancies, which leads to luminescence quenching. The prominent peaks of the TL glow curves of Li+ co-doped ZnO:RE3+ samples are found to be increased than that of ordinary ZnO:RE3+ samples. The peaks are also shifted towards the lower temperature from the peaks of ZnO:RE3+ due to the Li+ co-doping. The TL glow curves of the Li+ co-doped ZnO:RE3+ samples are found to obey first order kinetics. The samples are found to be very useful in thermoluminescence dosimetry.