Infrared-to-Visible Upconversion Imagers: Recent Advances and Future Trends

Infrared detection and imaging serve as powerful means in a wide range of fields such as automatic surveillance, biomedical imaging, and industrial inspection, extending human vision far beyond the visible world. Traditional infrared imagers based on rigid inorganic materials struggle to meet the dramatically increasing demand for high-performance infrared detectors, as their development and application are impeded by high manufacturing costs and complex fabrication processes. Upconversion devices that can directly convert invisible infrared input to visible images without pixel arrays and readout circuits have emerged as attractive alternatives to conventional infrared imagers. To date, continued explorations on novel materials and working mechanisms have enabled upconversion devices with excellent performances, low manufacturing costs, and compatibility with flexible and convenient fabrication methods, such as solution processing. This review focuses on the recent progress of upconversion imagers for infrared detection and visualization. We outline the fundamental working principles and the vital performance metrics of upconverters, then summarize and discuss the materials, strategies as well as fabrication process employed in state-of-the-art devices to effectively achieve long detection wavelength, high conversion efficiency, and enhanced resolution. Additionally, the diverse application scenarios are demonstrated. Lastly, the limitations and challenges are identified to promote the practical application of upconversion imagers. Specifically, the potential of infrared-to-visible upconversion imagers for improving immersive AR/VR interaction experiences is highlighted, providing new perspectives for the future development of upconversion imaging technology, which is very promising to advance compact, high-performance, and economical infrared imaging systems.