Microstructural and photoluminescence properties of sol-gel derived Tb3+ doped ZnO nanocrystals

Un-doped and Tb3+ doped ZnO nanocrystals with different concentrations of Tb3+ were synthesized by a sol-gel method and their photoluminescence (PL) properties were investigated. The successful incorporation of Tb3+ ions with different concentration (0.15, 0.5 and 1 mol %) in ZnO was realized and confirmed through different characterization. High crystalline ZnO products were produced without the need of a post-heat treatment. Elemental mapping conducted on the as prepared samples using Scanning electron microscope (SEM) equipped with energy dispersive X-ray spectrometer (EDX) revealed homogeneous distribution of Zn, O, and Tb ions. The high resolution transmission electron microscope (HR-TEM) analyses indicated that the un-doped and Tb3+ doped samples were composed of homogeneously dispersed particles of high crystallinity with an average size ranging from 3 to 6 nm in diameter, which was in agreement with X-ray diffraction (XRD) analyses. Raman spectroscopy was used to further elucidate the wurtzitic structure of the prepared samples. PL study revealed that among different Tb3+ concentrations, 0.5 mol% Tb3+ doped ZnO nanoparticles showed clear emission from the dopant originating from the 4f-4f intra-ionic transitions of Tb3+ while the broad defects emission was dominating in the 0.15 and 1 mol% Tb3+ doped ZnO. Optical band gap was extrapolated from the Ultraviolet Visible spectroscopy (UV-Vis) absorption analysis using TAUC's method and the widening of the optical band gap for the 0.15 and 0.5 mol% Tb3+ doped samples and the reduction of the optical band gap for the 1 mol% Tb3+ doped sample as compared to the un-doped sample was observed. Energy transfer mechanism between Tb3+ and ZnO is discussed in detail.