Modification on populating paths of β-NaYF4:Nd/Yb/Ho@SiO2@Ag core/double-shell nanocomposites with plasmon enhanced upconversion emission

Nd/Yb/Ho-doped hexagonal NaYF4 nanocrystals were synthesized and excited at 808 nm to avoid an overheating effect under 980 nm laser excitation. A core/double-shell nanocomposite (NaYF4:Nd/Yb/Ho@SiO2@Ag nanoparticles) was then developed to enhance upconversion luminescence intensity. The fabricated system exhibited a metal-induced effect and was used to determine the influence of SiO2 layer thickness on upconverting optical properties. SiO2 layer with different thicknesses were used to adjust the distance between NaYF4 nanocrystals and the outer layer of Ag nanocrystals. The largest enhancement of upconversion luminescence occurred when 10 nm-thick SiO2 shell was used, with enhancement factors of 15 and 7.5 for green and red emissions, respectively. Results indicated that the degree of luminescence enhancement was correlated with the competition of the three interactions occurred between fluorophores and metal NPs. After coating with Ag nanoparticles, some modifications were found on the upconversion processes of NaYF4 core nanoparticles and the underlying mechanisms were discussed respectively. The controllable upconversion luminescence renders metal-upconverted nanocomposites as suitable for bioassay, bioimaging, and energy conversion applications, which require high sensitivity and low background. (C) 2016 Optical Society of America