A dual-functional upconversion core@shell nanostructure for white-light-emission and temperature sensing

Abstract

A strategy to simultaneously achieve white-light-emission and temperature sensing via a 980 nm excitable upconversion core@shell nanoarchitecture design was provided. Specifically, the prepared Yb/Ho/Ce: NaGdF₄@Yb/Tm: NaYF₄ active-core@active-shell nanocrystals enabled the spatially confined doping of Ho³⁺ in the core and Tm³⁺ in the shell and thus greatly reduced the adverse energy transfers between them, leading to intense upconversion emissions for both Ho³⁺ and Tm³⁺ activators. Notably, introducing Ce³⁺ into the core resulted in the competition of radiation transitions from the Ho³⁺: ⁵S₂, ⁵F₄ green-emitting states and Ho³⁺: ⁵F₅ red-emitting one, which was beneficial to tune the red to green intensity ratio and ultimately realize white-light luminescence. Temperature-dependent upconversion emission spectra of the core@shell samples evidenced the joint contribution of Ce³⁺ in the core and Tm³⁺ in the shell to improve sensitivity for temperature detection. As a consequence, the core@shell nanostructure was demonstrated to have a high temperature sensitivity (2.4% K⁻¹) and excellent signal discriminability (3040 cm⁻¹), being potentially applicable as an optical thermometric material.