LAUSR

Near‐infrared (NIR) luminescence materials with broadband emissions are necessary for the development of light‐emitting diodes (LEDs) based light sources. However, most known NIR‐emitting materials are limited by their low external quantum efficiency. This work demonstrates how the photoluminescence quantum efficiency of europium‐activated calcium oxide (CaO:Eu) NIR phosphor can be significantly improved and stabilized at operating temperatures of LEDs. A carbon paper wrapping technology is innovatively developed and used during the solid‐state sintering to promote the reduction of Eu3+ into Eu2+. In parallel, the oxygen vacancies in the CaO lattice are repaired utilizing GeO2 decomposition. Through this process, a record‐high external quantum efficiency of 54.7% at 740 nm is obtained with a thermal stability greatly improved from 57% to 90% at 125 °C. The as‐fabricated NIR‐LEDs reach record photoelectric efficiency (100 [email protected]%) and output power (100 mA @ 319.5 mW). This discovery of high‐performance phosphors will open new research avenues for broadband NIR LED light sources in a variety of photonics applications.