Near-infrared organic lasers with ultra-broad emission bands by simultaneously harnessing four-level and six-level systems

Organic lasers with broad emission bands in near-infrared (NIR) region are crucial for their applications in laser communication, night-vision as well as bioimaging owing to the abundance of selectable lasing wavelengths. However, for most organic gain materials, gain regions are limited in a small wavelength range because of the fixed energy level systems. Herein, we design a strategy to realize NIR organic lasers with broad emission bands based on tunable energy level systems induced by cascaded excited-state intramolecular proton transfer (ESIPT). A novel gain material named DHNN was developed, which can undergo a cascaded double-ESIPT process supporting four-level and six-level systems simultaneously. By doping DHNN into polystyrene microspheres, NIR lasers with tunable emission bands can be achieved based on the careful modulation of microcavities. Finally, organic lasers with an ultra-broad emission band ranging from 700 to 900 nm was successfully achieved by harnessing four-level and six-level systems simultaneously.