Comparative Structural, Optical, and Photoluminescence Studies of YF3:Pr, YF3:Pr@LaF3, and YF3:Pr@LaF3@SiO2 Core-Shell Nanocrystals

Praseodymium (Pr3+)-doped YF3 (core) and LaF3-covered YF3:Pr (core-shell) nanocrystals (NCs) were prepared successfully by an ecofriendly, polyol-based, co-precipitation process, which were then coated with a silica shell by using a sol-gel-based Stober method. X-ray diffraction (XRD), transmission electron microscopy (TEM), thermal analysis, Fourier transform infrared (FTIR), UV/vis, energy bandgap, and photoluminescence studies were used to analyze the crystal structure, morphology, and optical properties of the nanomaterial. XRD and TEM results show that the grain size increases after sequential growth of crystalline LaF3 and the silica shell. The silica surface modification enhances the solubility and colloidal stability of the core-shell-SiO2 NCs. The results indicate that the surface coating affects the optical properties because of the alteration in crystalline size of the materials. The emission intensity of silica-modified NCs was significantly enhanced compared to that of core and core-shell NCs. These results are attributed to the formation of chemical bonds between core-shell and noncrystalline SiO2 shell via La-O-Si bridges, which activate the "dormant" Pr3+ ions on the surfaces of the nanoparticles. The luminescence efficiency of the as-prepared core, core-shell, and core-shell-SiO2 NCs are comparatively analyzed, and the observed differences are justified on the basis of the surface modification surrounding the luminescent seed core NCs.