White-emitting orthosilicate phosphor α-Sr2SiO4:Ce3+/Eu2+/K+: a bimodal temperature sensor with excellent optical thermometric sensitivity

Abstract

Non-contact temperature sensors with low cost, high reliability and high sensitivity have attracted increasing research interest in recent years. In this study, we synthesized a bimodal optical temperature sensor Sr₂SiO₄:Ce³⁺/Eu²⁺/K⁺ with excellent thermometric sensitivity through a high-temperature solid-state reaction method. In the matrix of α-Sr₂SiO₄, Ce³⁺ luminescence exhibits excellent thermal stability (∼129.1%@250 °C), while Eu²⁺ shows strong thermal quenching (∼21.7%@250 °C), leading to a significant change in the fluorescence intensity ratio (FIR) of Ce³⁺ (437 nm) and Eu²⁺ (550 nm) as a function of temperature. This feature enables the phosphor exhibiting outstanding sensitivity in the temperature range of 298–523 K. To be exact, it demonstrates a maximal relative sensitivity of 0.93% K⁻¹ at 348 K. Its absolute sensitivity linearly increases and reaches 3.46% K⁻¹ at 523 K. Besides, it has a large chromaticity shift (ΔE = 228 × 10⁻³ in 298–523 K) against temperature, making the temperature change visible to the naked eye. We first demonstrate a CIE chromaticity coordinate technique for temperature sensing with high accuracy and good sensitivity by using the function of x or (x² + y²)^0.5 against T. These unique optical thermometric features allow Sr₂SiO₄:Ce³⁺/Eu²⁺/K⁺ to serve as an accurate and reliable thermometer probe candidate for temperature sensing applications.