Enhanced Energy-Transfer Properties in Core-Shell Photoluminescent Nanoparticles Using Mesoporous SiO2 Intermediate Layers

Abstract

Multi-layer core-shell nanoparticles (YVO₄:Nd³⁺/mSiO₂/SiO₂) consisting of silica cores (SiO₂), mesoporous silica (mSiO₂) intermediate layers, and Neodymium doped rare-earth phosphor (YVO₄:Nd³⁺) shell layers were successfully synthesized using the stepwise sol-gel method. The morphological structure and optical properties of the functional core-shell nanoparticles were characterized and evaluated by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) analysis. mSiO₂ intermediate layers were utilized as the bridge between the core and shell materials. Their porous surfaces served to anchor the YVO₄:Nd³⁺ crystals. This prevents energy loss during the energy transfer of electrons, resulting in improved optical properties. The use of intermediate layer combinations of mSiO₂/SiO₂ in the coreshell structure also improved cost-effectiveness, because the core is filled with cheap silica, not expensive phosphors. Even though the nanoparticles used only a thin layer of the photoluminescent shell materials, the optical properties, resulting from the energy-transfer emitting mid-infrared light, were remarkably enhanced by increasing the crystallinity of the phosphor. To demonstrate the practical use of the synthesis method, the photoluminescent properties of the core-shell nanoparticles were optimized by adjusting the annealing temperature and scaling to mass production. We believe that our efficient synthetic strategy provides a facile way of obtaining functional, cost-effective core-shell nanoparticles with improved photoluminescent properties.