Interfacial Energy Transfer in Hollow Double-Shelled TiO2:x%Eu3+@SiO2:y%Tb3+ Nanospheres for Tissue Imaging

In this paper, hollow double-shelled TiO2:x%Eu3+@SiO2:y%Tb3+ nanospheres (C1–Ti-x/Si-y) were fabricated using carbon spheres as hard template followed by a two-step sol–gel coating process. The results demonstrate that there is strong interaction between the inner TiO2 layer and outer SiO2 layer, which can be characterized by the high surface content of Ti–O–Si bonds. The strong interaction makes it possible to achieve efficient energy transfer from Tb3+ to Eu3+ ions through crossing the double-shelled interface. The interfacial energy transfer (IET) efficiency from Tb3+ to Eu3+ ions is strongly influenced by the doping concentration of Eu3+ ions whose maximum is determined to be 30.2%. Furthermore, the surface of inner TiO2 layer is modified by the outer SiO2 layer through this strong interaction, which significantly enhances the emission intensity and suppresses the concentration quenching of Eu3+ ions. Under 377 nm excitation, C1–Ti-x/Si-y simultaneously exhibits red and green emissions derived from Eu3+ and Tb3+ ions, respectively. Moreover, by varying the doping concentration of Tb3+ and Eu3+ ions, the luminescence color of the samples can be tuned from green to orange and red. The characterization results show that our proposed phosphors may provide potential applications in tissue imaging.