Impact of LaF3 and silica shell formation on the crystal, optical and photo-luminescence properties of LaF3:Ce/Tb nanoparticles

摘要

LaF3:Ce/Tb and LaF3:Ce/Tb@LaF3 core and core/shell nano-structures were synthesized by the polyol process at low temperature. X-ray diffraction patterns, transmission electron microscopy images, energy dispersive X-ray, FTIR, UV/Vis, and photoluminescence spectra and band gap energy were used to investigate the impact of shell formation on the crystal structure, opto-electronic, photoluminescence and lifetime properties of the core-nanoparticles (core-NPs). The TEM image shows that the as-prepared luminescent core and core/shell/SiO2-NPs consist of polycrystals aggregated with a narrow size distribution, which can be easily dispersed in aqueous and non-aqueous solvents to form a transparent colloidal solution. The TEM image illustrated that the core and core/shell/SiO2 NPs are irregular hexagonals with a mean diameter of 20-35 nm. It is observed that the band gap energy gradually decreased after shell formation which may be due to the decreased crystallinity of the luminescent nanoproducts. The excitation spectra show a characteristic charge transfer transition of Ce~3+ 4f-5d(275) and all excitations of Tb~(3+) ~7F_6 - ~5D_j(7D_j = 1-6) ions, respectively. The excitation, emission and decay time clearly revealed that the luminescence efficiency was greatly enhanced after inert shell formation, whereas after silica surface modification the luminescence efficiency decreased because non-radiative decay is higher in core and core/shell NPs.