Influence of surface coating on the upconversion emission properties of LaPO4:Yb/Tm core-shell nanorods

A solution based hydrothermal method is used for the preparation of LaPO4 : Yb-Tm doped and LaPO4:Yb/Tm core-shell upconverted nanorods. The morphologies, structure, formation mechanism, and upconversion emission properties of these nanocrystals are investigated in detail. Tensile strain is observed for LaPO4:Yb-Tm doped material but compressive strain is obtained for LaPO4:Yb/Tm core-shell material. Analysis suggests that the lattice strain plays an important role on the upconversion emission. Bright blue (475 nm) and red (650 nm) upconversion emissions associated to (1)G(4) -> H-3(6) and F-3(2) -> H-3(6) transitions were observed and a significant higher in upconversion emission intensity is observed in core-shell nanorods. The effective decay time calculated are 230 and 110 mu s for core-shell and doped nanorods, respectively, indicating the removal of surface defects due to surface coating. It reveals that the core-shell structure shows better upconversion emission efficiency. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3143890]