Advances in infrared visualization via photoelectric upconversion

Photoelectric upconversion for infrared visualization detection is an emerging and transformative area in optoelectronics, enabling the perception of light beyond the visible spectrum. This technology integrates a near-infrared (NIR) or short-wave infrared (SWIR) photodetector (PD) with a visible light-emitting diode (LED) within a single device, facilitating the direct conversion of infrared photons to electrons and subsequently to visible photons. This innovative approach marks a significant departure from traditional pixelated sensor technologies, offering numerous advantages such as non-invasive, real-time imaging; enhanced sampling ease; compact and possibly flexible designs; and the capability to extend the human visual range. As a result, photoelectric upconversion techniques have shown tremendous potential across multiple fields, including biomedical diagnostics, public safety, national defense, and advanced industrial inspection.This review comprehensively explores the latest research developments in this rapidly evolving field. We begin by dissecting the fundamental components of infrared upconversion devices (UCDs), providing detailed insights into their material systems, device architectures, and operational mechanisms. The materials landscape is systematically categorized and critically analyzed, encompassing organic semiconductors, quantum dots (QDs), perovskites, and two-dimensional materials. Each material class is examined for its unique advantages and constraints. For example, organic materials are valued for their cost-effective processing and mechanical flexibility, while quantum dots offer tunable band gaps that significantly enhance detection capabilities into the SWIR range. Our discussion highlights the remarkable research progress originating from advancements in materials science and device physics, showcasing how organic materials have achieved substantial improvements in optoelectronic performance through their synthetic adaptability. Moreover, we underscore the achievements of QD-based UCDs, which have facilitated access to longer wavelengths, although challenges regarding material toxicity and stability persist. An essential architectural innovation is the introduction of multi-unit tandem structures, which involve stacking multiple PD or LED subunits to optimize the utilization of photogenerated charge carriers. This architectural development increases both upconversion efficiency and operating voltage beyond conventional limitations.Aside from examining the core optoelectronic performance, we consider the broadening application prospects of UCD technology. Its practical value has been validated across various real-world scenarios, such as biomedical monitoring techniques that include photoplethysmography (PPG) for heart rate and blood oxygen saturation measurements, as well as non-invasive vascular imaging, where non-invasive capabilities prove critical. The integration of UCDs into wearable devices has led to developments in smart eyewear and anti-surveillance technologies for augmented reality and security applications. Furthermore, their incorporation into interactive color displays and multifunctional optical communication systems demonstrates key benefits, including low power consumption, high resolution, and the potential for large-area, pixelless imaging.Finally, we summarize current challenges in achieving widespread commercialization of this promising technology, such as the limited spectral range and environmental stability of specific materials, the pursuit of higher efficiency under weak light conditions, and the complexities of scalable manufacturing and integration processes. We propose forward-looking solutions that emphasize the importance of innovative material design, precise device engineering, and optimized fabrication techniques, aiming to provide a robust theoretical framework and practical guidance for the future optimization and real-world application of high-performance infrared imaging devices.