Structural characterizations and up-conversion emission in Yb3+/Tm3+ co-doped ZnO nanocrystals by tri-doping with Ga3+ ions

ZnO:Yb3+,Tm3+,Ga3+ up-conversion nanoparticles (UCNPs) with sizes of between 20 and 65 nm are synthesized by the hydrothermal method. The size of the nanocrystals is affected by different Ga3+ concentrations. The variation in size has influence on the particles' visible blue and red up-conversion (UC) emission. In this paper, X-ray powder diffraction results show different amounts of gallium substituting for Zn in the ZnO lattice. When the concentration of Ga3+ is 3 mol%, the resulting UCNPs exhibit strong UC emission, longer fluorescence lifetime and narrower band gap. Due to their adjustable size and UC fluorescence properties, ZnO:Yb3+,Tm3+,Ga3+ nanocrystals have broad prospects for future applications in the biomedical field.