[Upconversion properties of sodium and aluminum fluorides coated BaF2 material].

Sodium and aluminum fluorides coated BaF2 was synthesized by hydrothermal method. It was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and fluorescence spectrophotometer, respectively. The analysis results indicated that sodium and aluminum fluorides existed in the form of sodium fluoride and sodium fluoroaluminate, which combined with BaF2 surface via chemical bonds, and exhibited coated structure. Fluorescence spectroscopy testing showed that there were two wide upconversion emission peaks with maxima at 304 and 324 nm under the excitation at 583 and 863 nm, respectively. Its phosphorescence life time was greater than 18.4 ms, and the emission intensity exhibited a rising process from the beginning and a decaying process after 15 ms. The luminescence mechanism was proposed according to the energy conversion process of the upconversion emission, the results showed that the upconversion emission belonged to the quantum confinement effect-interface light emission center radiative recombination.

[Preparation and luminescent performance of Tb3+ doped SiO2 core-shell nanoparticles].

The authors synthesized the core-shell nanoparticles of SiO2-coated SiO2:Tb3+ by using sol-gel method (SiO2:Tb3+ @SiO2), and studied the influence of core-shell ratio and preparation craftwork on its luminescence properties. The photograph of TEM and EDS showed that SiO2:Tb3+ were coated successfully by SiO2. The authors found that the samples of SiO2:Tb3+ @SiO2 prepared by mixing of core and shell after shell aging with the ratio of core/shell being 1.2 g/25 mL had the stronger fluorescence intensity. Time-resolved spectra showed that the SiO2:Tb3+ @SiO2 had longer fluorescence life time than SiO2:Tb3+.