Self-calibrated optical thermometer LuNbO4:Pr3+/Tb3+ based on intervalence charge transfer transitions

Abstract

A Pr³⁺/Tb³⁺ co-doped LuNbO₄ phosphor was synthesized as a self-calibrated optical thermometer using a high-temperature solid-state method, and its structure and luminescent property were elaborately investigated. Under intervalence charge transfer (IVCT) excitation at 305 nm, the sample LuNbO₄:Pr³⁺/Tb³⁺ exhibited several bands in the green and red regions, originating from characteristics transitions of Pr³⁺ and Tb³⁺ ions. Through monitoring thermo-responsive emission intensity ratios from the ¹D₂ → ³H₄ (Pr³⁺) and ⁵D₄ → ⁷F₅ (Tb³⁺) transitions, sensitive thermometry with good signal discriminability was achieved in phosphor LuNbO₄:Pr³⁺/Tb³⁺ owing to a significant difference in thermal activation energy between Pr³⁺ and Tb³⁺ under IVCT excitation. Moreover, the maximum absolute sensitivity and relative sensitivity reached about 0.024 K⁻¹ at 493 K and 1.26% K⁻¹ at 463 K, respectively, for the LuNbO₄:Pr³⁺/Tb³⁺ sample, which implies that the present phosphor could be considered as a promising candidate for self-calibrated optical thermometers.