Chromium Ion Pair Luminescence: A Strategy in Broadband Near-Infrared Light-Emitting Diode Design.

Portable near-infrared (NIR) light sources are in high demand for applications in spectroscopy, night vision, bioimaging, and many others. Typical phosphor designs feature isolated Cr ion centers, and it is challenging to design broadband NIR phosphors based on Cr-Cr pairs. Here, we explore the solid-solution series SrAlGaO:0.12Cr ( = 0, 2, 4, 6, 8, 10, and 12) as phosphors featuring Cr-Cr pairs and evaluate structure-property relations within the series. We establish the incorporation of Ga within the magentoplumbite-type structure at five distinct crystallographic sites and evaluate the effect of this incorporation on the Cr-Cr ion pair proximity. Electron paramagnetic measurements reveal the presence of both isolated Cr and Cr-Cr pairs, resulting in NIR luminescence at approximately 650-1050 nm. Unexpectedly, the origin of broadband NIR luminescence with a peak within the range 740-820 nm is related to the Cr-Cr ion pair. We demonstrate the application of the SrAlGaO:0.12Cr phosphor, which possesses an internal quantum efficiency of ∼85%, a radiant flux of ∼95 mW, and zero thermal quenching up to 500 K. This work provides a further understanding of spectral shifts in phosphor solid solutions and in particular the application of the magentoplumbites as promising next-generation NIR phosphor host systems.