Optoelectronic thermometer based on microscale infrared-to-visible conversion devices
Temperature sensing with the high spatial and temporal resolution is crucial in a variety of disciplines, including industrial manufacturing, environmental monitoring, and healthcare monitoring.
Because of their benefits of distant detection, minimum intrusion, tolerance to electromagnetic interference, and high resolution, optical-based sensors are promising choices for temperature monitoring in biological diagnostics. Luminous intensity, wavelength, peak width, and/or decay duration can all be used to create optical sensing modalities.
The upconversion mechanism reduces biological autofluorescence, improves tissue penetration, and produces clearly observable and capturable visible light signals, making it a more acceptable tool for biological sensing.
In a new paper published in Light Science & Application (“An Optoelectronic thermometer based on microscale infrared-to-visible conversion devices”), a team of scientists, led by Dr. He Ding from the School of Optics and Photonics, Beijing Institute of Technology, Prof. Xing Sheng from Department of Electronic Engineering, Tsinghua University, and co-workers have developed an optoelectronic NIR-to-visible upconversion device based on designed semiconductor heterostructures, exhibiting a linear response, fast dynamics, and low excitation power.
The optoelectronic upconversion device’s temperature-dependent photoluminescence properties are extensively explored, and its capacity for thermal sensing is proven.
The proposed temperature sensing strategy is based on a fully integrated optoelectronic upconversion device (Figure 1a), which consists of a low-bandgap gallium arsenide (GaAs) based double junction photodiode and a large-bandgap indium gallium phosphide (InGaP) based light-emitting diode (LED) connected 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 lithographically specified and epitaxially released microscale devices (size 300300 m2) achieve efficient NIR-to-visible upconversion with a linear response and rapid dynamics, as previously established (Figure 1c)
The red emission of the optoelectronic upconversion device is accompanied by a decreasing intensity and a redshift of the emission peak from 625 nm to 637 nm with rising temperature under near-infrared light stimulation in the wavelength range of 770–830 nm (Figure 2a).
(a) Excitation and upconverted photoluminescence (PL) emission spectra at different temperatures (25–90 °C). (b) Peak wavelength and PL intensity of the upconverted red emission as a function of temperature, calculated (dash line) and observed (dots), with the shaded range representing the standard deviation recorded among 10 samples. (Photo courtesy of the study’s authors).
An intensity-temperature sensitivity of 1.5 percent °C-1 and a spectrum-temperature sensitivity of 0.18 nm °C-1 were calculated based on synergic variables attributed to the material’s properties and structure design (Figure 2b).
The authors propose many uses for such a robust optoelectronic upconversion optical thermometer: “We can accomplish spatially resolved heat-sensing using a large-area device array of optoelectronic upconversion devices” (Figure 3a). For example, we utilize air cannons to create hot airflow that blows on the sample, disrupts the upconversion emission, and finally extinguish it. We can acquire the geographical distribution and real-time changes in temperature based on the connection between emission intensity and temperature,” stated He Ding of Beijing Institute of Technology.
Graph 3. (a) Temperature mapping and spatially resolved PL responses of a device array under nonuniform heating (left) (right). (b) On the left, a photo of the fibre sensor used to measure exhaling temperature. Right: Dynamic temperature signals acquired by the fibre sensor based on emission peak wavelength shifts and PL intensity variations during cyclic exhaling actions, compared to data simultaneously recorded by the thermocouple. The grey areas reflect exhalation activities. (c) On the left, a photo of a behaving mouse with a fibre sensor and a thermocouple implanted in the brain for temperature monitoring. Right: Dynamic temperature data produced by the fibre sensor in the mouse brain based on emission peak wavelength shifts and PL intensity variations, compared to thermocouple values. The shaded gray region represents the time period when the mouse is placed in a hot environment at around 40 ºC. (Image courtesy of the researchers)
“The upconversion device may be removed from the produced substrate and combined with fibre optics to create light-guided heat sensors,” says the researcher. Such an optical-based technology, in addition to tethered electrical sensors, is better ideal for usage in areas with severe electromagnetic interferences, and is especially capable of acquiring data during magnetic resonance imaging (MRI). As a proof-of-concept demonstration, such a fiber-coupled, portable system may be easily implemented for biomedical applications, such as monitoring the exhalation behaviour of human and deep tissue with the implantation in the mouse brain (Figures 3b and 3c).” Tsinghua University’s Xing Sheng stated
“The MRI-compatible, implanted sensors paired with fibre optics have both research and therapeutic implications, with the possibility for deep-body temperature monitoring.” These materials and device concepts provide a powerful toolkit with a wide range of uses in the environment and healthcare.” Xing Sheng came to a conclusion and made a prediction.