Visualization of near-infrared light and applications

Development of high performance near-infrared (NIR) visualization devices offers an exciting opportunity for a plethora of applications in bio imaging, food, wellness, surveillance, and environmental monitoring. NIR visualization devices include an NIR photodetector (PD) unit monolithically integrated with a visible light-emitting diode (LED) unit, enabling the direct visualization of the incident invisible NIR light. In a NIR visualization device, the NIR PD unit serves as one of the charge-injection layers in the LED unit. The hole-electron current balance in the NIR visualization device is controlled by the photocurrent generated in the NIR PD in the presence of the NIR light. The visible light emission in the LED unit is observed in area where the effective charge injection occurs, adjusted by the NIR PD unit in the presence of the NIR light, such that the objects reflecting or illuminating NIR light can be visualized. Likewise, the charge injection in the LED unit can be suppressed in the absent of NIR light or it is reduced due to the decrease in photocurrent in the NIR PD unit, e.g., the presence of the NIR absorbing materials that partially block the NIR light. This review provides a comprehensive overview discussing the operation principle of the NIR visualization devices and the recent progresses made in different types of NIR visualization devices prepared using different inorganic, organic functional semiconductor materials and their combinations. The photon-to-photon conversion efficiency is highly dependent on the quantum efficiency of the NIR PD unit and the LED unit in the NIR visualization device. The efforts and progresses in the development of a series of NIR visualization devices and the applications in 3D image analysis, NIR detection card, bio images, health and environmental monitoring and detection are presented.