Synthesis and photocatalytic activity of δ-doped hexagonal NaYF4:Yb,Tm@TiO2/RGO nanocrystals

Abstract

Enhancement of the luminescence efficiency of up-conversion nanocrystals is essential for the development of near-infrared (NIR)-responsive photocatalysts. In this study, δ-doped hexagonal NaYF₄:Yb,Tm@TiO₂ (β-NaYF₄:Yb,Tm@TiO₂) nanocrystals, with the dopant ions Tm³⁺ and Yb³⁺ in two-dimensional planes, integrated with reduced graphene oxide (RGO) nanosheets were synthesized by a simple solvothermal process and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), luminescence and ultraviolet absorption spectroscopy. The core, inner shell and outter shell of the δ-doped β-NaYF₄:Yb,Tm are in the most efficient host structure phase, with a diameter of 29 nm and thicknesses of 6.4 and 1.2 nm, respectively. The δ-doped β-NaYF₄:Yb,Tm exhibits about a 13 times increase in the luminescence intensity than the bare β-NaYF₄:Yb,Tm due to the effective reduction of both the surface and inner defects around Yb³⁺. Moreover, the δ-doped β-NaYF₄:Yb,Tm@TiO₂/RGO exhibits significantly enhanced photocatalytic activity in the degradation of rhodamine B (RhB) under both NIR and UV irradiation. Our results highlight that the δ-doping construction of the most efficient host structure is promising for developing NIR-responsive photocatalysts.