Controllable synthesis and size-dependent upconversion luminescence properties of Lu2O3:Yb3+/Er3+ nanospheres

Lu2O3:Yb3+/Er3+ nanocrystals with various sizes and shapes (nano-aggregates, sub-micrometer wires, and nanospheres) have been synthesized by the soft chemistry coprecipitation route. By regulating the reactant ratio of rare earth to urea precipitant ([RE3+]/(NH2)(2)CO), uniform spherical Lu2O3:Yb3+/ Er3+ nanoparticles with the sizes of 45, 100, 165, 200, and 250 nm were obtained in the experiments. The phases, morphologies, as well as the luminescence properties of as-prepared samples were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and upconversion luminescence (UCL) spectra, respectively. Under the excitation of a 980 nm diode laser, the Lu2O3:Yb3+/Er3+ samples showed size-dependent upconversion luminescence property. From the results of Fourier transform infrared (FTIR) spectra and dynamical analysis, it was confirmed that the surface effect is dominant in influencing the UCL of Er3+ in the spherical Lu2O3:Yb3+/Er3+ samples. By coating Lu2O3:Yb3+/Er3+ nanospheres with different shell layers, UCLs of Er3+ were changed greatly in these core-shell samples. The possible physical mechanism involved in size/surface-dependent upconversion processes was discussed in detail.