Judd-Ofelt analysis, photoluminescence and photocatalytic properties of core-shell SiO2@TiO2:Eu3+ nanospheres with different diameters

SiO2@TiO2:Eu3+ nanospheres with different diameters were fabricated by a surfactant-free sol-gel process. The influence of the diameter of SiO2 on photocatalytic and luminescence properties of SiO2@TiO2:Eu3+ nanospheres has been investigated in detail. The sample with the biggest diameter exhibits the strongest red emission and the highest photocatalytic efficiency on degradation of methyl orange. The structure, phase composition and grain size were determined using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results show that the grain size of TiO2 increases with the increase of SiO2 size owing to a relatively smaller curvature. In addition, CS-621 (the sample with the biggest diameter) with varied Eu3+ ions concentrations ranged from 2% to 18% were prepared to investigate the optimum luminescence behavior and concentration quenching effect of Eu3+ ions, most interestingly, the higher doping concentration of Eu3+ ions can accelerate the phase transformation of TiO2 from anatase to rutile. Moreover, Judd-Ofelt (J-O) parameters were calculated to study the site symmetry and coordination environment of Eu3+ ions. The core-shell structured and size tuned bifunctional SiO2@TiO2:Eu3+ nanospheres provide a platform for fabricating other new functional materials and can be applied in the fields of W-LEDs, biological imaging, photocatalysis, etc.