Competitive sensitization effect towards Luminescence-tuned Lanthanide-doped TiO2/SiO2 Core-shell nanoparticles for enhanced responsivity oxygen detection

Abstract

The luminescence of TiO2 doped with Sm3+ can be excited through TiO2 band-to-band absorption, which exhibits oxygen sensitivity. However, its carrier behaviors and oxygen sensing mechanism have not yet been clarified, which inhibits the further improvement of sensitivity. In this study, using Eu3+ ions as an “energy level probe,” we demonstrated a novel strategy using a C@SiO2:2%Sm3+@TiO2 hollow double-shell nanostructure containing surface oxygen vacancies, designated a competitive sensitization effect for the first time. Density-functional theory combined with the experimental results revealed the carrier behaviors and oxygen sensing mechanism. Further, we demonstrated that the charge state of oxygen vacancies is controlled by the adsorption and desorption of dioxygen molecules, which affects electron relaxation and indirectly affects the luminescent behaviors. The effective exploitation of the competitive sensitization effect and revelation of the oxygen sensing mechanism ensured that the excitation of Sm3+ in C@SiO2:2%Sm3+@TiO2 can be controlled by the ambient oxygen concentration. Therefore, compared to the widely reported Sm3+-doped TiO2, C@SiO2:2%Sm3+@TiO2 demonstrated increased oxygen sensitivity (by over three folds) with a detection minimum of sub-100 ppm. Moreover, as ambient oxygen concentration changes, the luminescence color of the films prepared by using C@SiO2:2%Sm3+@TiO2 and commercial blue phosphors changes significantly (from pink to blue).