Photocatalytic and Photoluminescence Properties of Core–Shell SiO₂@TiO₂:Eu³⁺,Sm³⁺ and Its Etching Products

A novel multifunctional core–shell, yolk–shell SiO 2 @TiO 2:Eu 3+ /Sm 3+ and hollow TiO 2:Eu 3+ /Sm 3+ structures were successfully synthesized. The relationship between morphology/ions doping and multifunctional properties including photoluminescence and photocatalysis has been discussed in detail for the first time using systematic characterization techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), photoluminescence (PL), ultraviolet–visible light (UV-vis) analysis, Fourier transform infrared (FT-IR) spectroscopy, Brunauer–Emmett–Teller (BET) surface area analysis, and X-ray photoelectron spectroscopy (XPS). Upon ultraviolet (UV) excitation, the products show the characteristic red and orange–red emission lines of Eu 3+ and Sm 3+, respectively. In addition, Judd–Ofelt intensity parameters (Ω 2, Ω 4 ) were used to investigate the symmetry and coordination state of Eu 3+ ions in the products with different morphologies. The relative luminescence intensities were in the following order: yolk–shell > core–shell > hollow structure. This phenomenon can be ascribed to the unique yolk–shell configuration, which possesses appropriate interior cavity used for multiple reflections and scattering, allowing for more-efficient utilization of the light. Moreover, compared with yolk–shell and hollow structure, the core–shell spheres exhibit excellent photoactivity for the degradation of MO, because the existence of Ti–O–Si bonds increases the surface acidity of the sample, thereby activating the oxidation reaction. In addition, the electron activation in the TiO 2 matrix can be facilitated through intermediate oxygen atoms. Moreover, products doped with different rare-earth (RE 3+ ) ions exhibited distinguishable photocatalytic performance. The surfactant-free method provides a promising route toward the development of multifunctional materials for many applications in photocatalysis and PL.