Fabrication of core@spacer@shell Au_nanorod@mSiO₂@Y₂O₃:Er nanocomposites with enhanced upconversion fluorescence

Herein, we report the fabrication of well-defined Au_nanorod@mSiO₂@Y₂O₃:Er nanocomposites with a Au nanorod core, an Y₂O₃:Er shell, and mesoporous silica as spacer. The thickness of the mesoporous silica layer could be simply controlled by varying the reaction time and the amount of silica precursor. The nanocomposites were characterized by X-ray diffraction, transmission electron microscopy and UV-vis absorption spectroscopy. Thanks to the two distinct plasmon absorptions of the Au nanorod associated with the longitudinal and transverse surface plasmon resonances modes, the plasmon resonances matched very well to the absorption and emission wavelengths of Y₂O₃:Er in the near IR and visible regions, respectively. The strongest enhancement is observed when the optimized silica thickness is around 40 nm, resulting in about 10- and 8-fold enhancement for green and red emissions, respectively. Besides the enhanced upconversion fluorescence, the prepared nanocomposites with unique properties and functions offered by Au nanorod and mesoporous silica structure are expected to be useful in photothermal therapy, drug delivery, medical diagnostics and therapy.