Efficient Sr2Ta2O7:Bi3+,Ln3+ (Ln3+ = Eu3+,Sm3+) phosphors for optical thermometry and anti-counterfeiting†

Abstract

Designing multifunctional phosphors for optical thermometry and anti-counterfeiting remains a meaningful challenge. In this study, we present a series of Sr₂Ta₂O₇:Bi³⁺,Ln³⁺ (Ln³⁺ = Eu³⁺, Sm³⁺) luminescent materials for optical thermometry and anti-counterfeiting. Sr₂Ta₂O₇:Bi³⁺,Ln³⁺ phosphors were synthesized, and their crystal structure, luminescence properties, and energy transfer processes were investigated in detail. Under 310 nm excitation, Sr₂Ta₂O₇:Bi³⁺ exhibits blue light emission at 475 nm, due to the metal–metal charge transfer effect (MMCT) of the Bi³⁺ ions. Moreover, tunable multicolor luminescence was achieved by codoping Bi³⁺ and Ln³⁺ ions. A series of novel optical thermometers with an optimal relative sensitivity of 2.98% K⁻¹ were designed based on the luminescence of the Bi³⁺ and Ln³⁺ ions with different temperature sensitivities. High and low temperature cycling experiments demonstrated the reliability of the optical thermometer. Finally, potential applications in fingerprint anti-counterfeiting and discoloration behavior under UV light at different temperatures were explored. These results provide a model for integrating multifunctional optical applications into a single material.