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

Abstract

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 3+ ion centers, and it is challenging to design broadband NIR phosphors based on Cr 3+ –Cr 3+ pairs. Here, we explore the solid-solution series SrAl 11.88– x Ga x O 19:0.12Cr 3+ ( x = 0, 2, 4, 6, 8, 10, and 12) as phosphors featuring Cr 3+ –Cr 3+ 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 3+ –Cr 3+ ion pair proximity. Electron paramagnetic measurements reveal the presence of both isolated Cr 3+ and Cr 3+ –Cr 3+ 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 3+ –Cr 3+ ion pair. We demonstrate the application of the SrAl 5.88 Ga 6 O 19:0.12Cr 3+ 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.