An Optoelectronic thermometer based on microscale infrared-to-visible conversion devices

Thermometric detectors are crucial in evaluating the condition of target objects spanning from environments to the human body. Optical-based thermal sensing tools have received extensive attention, in which the photon upconversion process with low autofluorescence and high tissue penetration depth is considered as a competent method for temperature monitoring, particularly in biomedical fields. Here, we present an optoelectronic thermometer via infrared-to-visible upconversion, accomplished by integrated light receiving and emission devices. Fully fabricated thin-film, microscale devices present temperature-dependent light emission with an intensity change of 1.5% °C^-1 and a spectral shift of 0.18 nm °C^-1. The sensing mechanism is systematically characterized and ascribed to temperature dependent optoelectronic properties of the semiconductor band structure and the circuit operation condition. Patterned device arrays showcase the capability for spatially resolved temperature mapping. Finally, in vitro and in vivo experiments implemented with integrated fiber-optic sensors demonstrate real-time thermal detection of dynamic human activity and in the deep brain of animals, respectively.