Full Optical Contactless Thermometry Based on LED Photoluminescence

Abstract

In this work, we report a contactless temperature measurement method based on the photoluminescence (PL) of an AlInGaP light-emitting diode (LED) structure under open-circuit conditions. The proposed method has been evaluated between 90 and 460 K, but a broader temperature range is possible. The system is based on the temperature-dependent PL variation of a commercial AlInGaP LED designed to emit at 630 nm at room $T$ . The sample is placed inside a temperature-controlled cryostat equipped with a transparent glass window. After exciting the sample by means of a green 532-nm laser, the emitted PL spectrum has been collected by an optical fiber and acquired by means of a charge-coupled device (CCD) array spectrometer. In the first part of the work, the most effective calibration is discussed as a function of the properties of the sampled spectrum; both PL emission peak and spectral width have been considered to calculate the optimal estimated temperature. The effect of spectrometer resolution on temperature estimation has been evaluated by comparing and analyzing the results from two spectrometers with different pixel densities. The effects of excitation intensity and angular positioning have also been evaluated. Finally, uncertainty due to calibration, together with measurement accuracy and precision, has been calculated over 50 acquisitions resulting on average in ±1, ±0.7, and ±0.3 K, respectively, on a temperature range of 300 K.