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

Abstract

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)₂CO), 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.