Strategies to approach high performance in Cr3+-doped phosphors for high-power NIR-LED light sources

Optics: Visibly powerful near-infrared light-emitting diodes A near-infrared light-emitting (NIR-LED) diode that emits high-power light could pave the way for the development of next-generation monitoring and detecting devices. Although solid-state NIR-LEDs are used in such devices, their narrow emission band limits their range of applications. Broadband NIR-emitting phosphor-converted LEDs offer the best solution. However, creating NIR phosphors that are sufficiently excited by blue light is challenging. Now, a team of Chinese and American researchers, led by Yongfu Liu from the Chinese Academy of Sciences, has created a NIR-LED that emits light in the 700-900 nm with an output of 109.9 mW at 520 mA after excitation with blue light. The device has the highest recorded power rating to date and could be used in applications from bioimaging and night-vision technologies, to monitoring food and medicines. Broadband near-infrared (NIR)-emitting phosphors are key for next-generation smart NIR light sources based on blue LEDs. To achieve excellent NIR phosphors, we propose a strategy of enhancing the crystallinity, modifying the micromorphology, and maintaining the valence state of Cr3+ in Ca3Sc2Si3O12 garnet (CSSG). By adding fluxes and sintering in a reducing atmosphere, the internal quantum efficiency (IQE) is greatly enhanced to 92.3%. The optimized CSSG:6%Cr3+ exhibits excellent thermal stability. At 150 degrees C, 97.4% of the NIR emission at room temperature can be maintained. The fabricated NIR-LED device emits a high optical power of 109.9 mW at 520 mA. The performances of both the achieved phosphor and the NIR-LED are almost the best results until now. The mechanism for the optimization is investigated. An application of the NIR-LED light source is demonstrated.