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Thermal sensors based on optical cavities have extremely high precision spectrally resolved optical responses, but their measurements need complex spectrometric systems in stable fixtures, which restricts their biological uses.

Temperature-dependent color variations are also evident in phase-changing materials such as liquid crystals, although their apparent color might be limited by the surrounding illumination, viewing angles, polarizations, and other factors.

Photoluminescent (PL) materials or devices can be used to sense temperature, and the emission intensity, peak wavelength, decay lifetime, etc., are dependent on the temperature. Several optoelectronic devices based on designed semiconductor heterostructures have been developed for various optical sensing applications.

This study demonstrated the capability of an optoelectronic upconversion device for thermal sensing, and spatially resolved temperature mapping in ambient environments.

The suggested temperature sensing method is focused on a fully integrated optoelectronic upconversion device, schematically depicted in Figure 1a, comprising of a low-bandgap gallium arsenide (GaAs) based double junction photodiode and a large-bandgap indium gallium phosphide (InGaP) based light-emitting diode (LED) arranged in series.

The device structure, which was formed on a GaAs substrate with a sacrificial interlayer, is shown in Figure 1b as a cross-sectional scanning electron microscopy (SEM) picture.

The PL emission of the devices is temperature dependent. Figure 1d shows the device’s spectroscopic performance under steady-state NIR excitation at 770–830 nm.

Figures 1e shows device performance data from ten distinct devices.

These experimental results are quantitatively consistent with theoretical calculations based on a comprehensive diode balancing model and the empirical Varshni formula for the bandgap energy-temperature connection.

Read more: Optoelectronic Thermometer as an Alternative Approach for Temperature Sensing