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.