Upconversion emission enhancement in silica-coated Gd2O3:Tm3+, Yb3+ nanocrystals by incorporation of Li+ ion

Silica-coated Tm3+, Yb3+, Li+-tridoped Gd2O3 nanocrystals (GTYLS) were prepared by a reverse microemulsion method. The blue upconversion luminescence intensity of this nanocomposite was enhanced remarkably by the incorporation of Li+ ions as compared with that of lithium-free Gd2O3:Tm3+, Yb3+@SiO2 (GTYS) nanocomposites. X-ray diffraction patterns (XRD) of GTYS and GTYLS revealed that Gd2O3 were cubic, silica shell was noncrystalline. The transmission electron microscope (TEM) photographs showed that the core of GTYLS was crystalline with the size of 50–60 nm, and the size of silica shell was about 15 nm. FT-IR spectra indicated that the absorption bands of OH became weaker with increasing the concentration of Li+. The enhanced luminescence is due to the distortion of the local asymmetry around Tm3+ and the decrease of OH generated by Li+ ion incorporation in the lattices.