Abstract
The determination of temperature is essential in many applications in the biomedical, technological, and industrial fields. Optical thermometry appears to be an excellent alternative for conventional electric temperature sensors because it is a non-contact method that offers a fast response, electromagnetic passivity, and high temperature sensitivity. In this paper, we propose an optical thermometer probe comprising an Er3+/Yb3+ co-doped tellurite glass attached to the tip of an optical fibre and optically coupled to a laser source and a portable USB spectrometer. The ratio of the up-conversion green emission integrated peak areas when excited at 980 nm was temperature dependent, and it was used to calibrate the thermometer. The thermometer was operated in the range of 5–50 °C and 50–200 °C, and it revealed excellent linearity (r2 > 0.99), suitable accuracy, and precisions of ±0.5 and ±1.1 °C, respectively. By optimizing Er3+ concentration, we could obtain the high green emission intensity, and in turn, high thermal sensitivity for the probe. The probe fabricated in the study exhibited suitable properties for its application as a temperature sensor and superior performance compared to other Er3+ -based optical thermometers in terms of thermal sensitivity.
Highlights
Temperature is a fundamental parameter as it governs various chemical and physical intracellular interactions that occur in the life cycle of biological cells[1,2,3]
From the differential scanning calorimetry (DSC) curves recorded for the tellurite glass (TG) samples, we determined the glass transition temperature, Tg (±2 °C), the onset temperature of crystallisation, Tx (±2 °C), and the glass thermal stability against crystallisation, ΔT=Tx−Tg (±3 °C)
A portable optical thermometer based on the UC green fluorescence intensity ratio of an Er3+/Yb3+ co-doped tellurite glass was developed by exploring the radiative transition from the thermally coupled 2H11/2 and 4S3/2 excited levels to the 4I15/2 ground state of Er3+
Summary
Temperature is a fundamental parameter as it governs various chemical and physical intracellular interactions that occur in the life cycle of biological cells[1,2,3]. Sensors based on the temperature-dependent fluorescence intensity ratio (FIR) of active ion-containing hosts in different materials, such as glass ceramics[7], nanoparticles[9] and glasses[10], have been increasingly reported. Among RE3+, praseodymium[20], neodymium[21], europium[22], holmium[21], and erbium[18,23,24] have been used for optical temperature sensing because they generate emissions that are dependent on temperature owing to the presence of thermally coupled levels. Erbium ions have a thermally coupled pair of energy levels, 2H11/2 and 4S3/2, whose green emission intensity ratio varies with temperature, allowing it to act as a probe for measuring environmental temperature where it is inserted[29]. The use of an IR excitation source instead of an ultraviolet (UV) excitation source has the advantage of being commercially less expensive and more portable, in addition to being more suitable for biological applications
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