Sensitive Thermometry through Upconversion of Er³⁺, Yb³⁺ Codoped Silicate KLaSiO₄

With the increasing demand for precise temperature measurement, noncontact ratiometric fluorescence thermometry has gained significant attention due to its high accuracy and simplified calibration. The lack of an optimal optical thermometer encourages researchers to develop new ones. In this work, a new ratiometric fluorescent thermometer KLaSiO4:Er3+/Yb3+ synthesized by the sol–gel method is investigated. The phosphor exhibits excellent temperature characteristics in two luminescence modes: downconversion luminescence (excitation wavelength: 375 nm) and upconversion luminescence (excitation wavelength: 980 nm). These characteristics are systematically investigated in the temperature range of 80–773 K based on the luminescence intensity ratio. At 300 K, the relative sensitivity values are 0.7% K–1 for downconversion luminescence and 0.86% K–1 for upconversion luminescence, indicating that the phosphors hold great potential for multimode optical temperature sensing.