Abstract
Phosphors are the key enabling components for down-converted light emitting diodes (LEDs) which are regarded as the most efficient, cheapest and smallest broadband light sources1,2.Although myriad phosphors have been developed3–8, very few finally come into practical use in consideration of efficiency, stability and price. Unlike visible phosphors, broadband near-infrared (NIR) phosphors rarely achieved high efficiency and high stability9–13, and furthermore, they usually contain high content of rare-metal elements14–18, thus precluding NIR applications of phosphor-converted LEDs (pc-LEDs). Here, we report such a class of broadband NIR phosphors that possesses excellent luminescence properties while is free of rare-metal elements, by revealing weak-field octahedral sites for Cr3+ occupation in MgAl2O4 spinel that is conventionally believed to only offer strong-field octahedral sites. Such weak-field octahedral sites are attributed to the intrinsic cation inversion in the spinel structure, and can be finely engineered by superstoichiometric Al2O3. We further introduce SiO2 to break the inversion symmetry of octahedral sites for boosting the 3d–3d transition probabilities and thus the photoexcitation efficiency. The corresponding pc-LED prototype delivers bright and stable broadband NIR light with an optical power of 180.8 mW and a photoelectric efficiency of 16.0% at the rated current, more than two times those of the commercialized and reported counterparts, meaning a big step forward for broadband light sources.