Terbium and holmium codoped yttrium phosphate as non-contact optical temperature sensors

Abstract

Optical thermometry has attracted many studies for non-contact high-resolution real-time temperature sensing. Most promising approaches are based on the ratio of up-converted luminescence intensities of two thermally coupled excited states. Here, we proposed a new strategy utilizing the temperature dependence of the anti-Stokes luminescence by exciting a thermally populated low-lying state to the excited state. Our scheme not only retains the advantage of previous approaches in reducing noise from the Stokes-type stray light, but also has the advantage of high quantum yield as a result of a one-photon excitation process. The temperature-dependent luminescence of Tb³⁺, Ho³⁺ codoped YPO₄ is employed to demonstrate our scheme. The results show that, under a certain excitation, the emission of Tb³⁺ enhances dramatically while that of Ho³⁺ declines with increasing temperature. The sharp temperature-dependent intensity ratio was used to calibrate temperature. A maximum relative sensitivity of 2.51% K⁻¹ at 310 K was obtained, substantially superior to values previously reported for acknowledged optical thermometry phosphors. These results indicate that the YPO₄:Tb³⁺,Ho³⁺ can be a promising candidate to achieve accurate optical temperature sensing with a high sensitivity, and the mechanism proposed can be used to develop better optical thermometry.