Data-Driven Discovery of Broadband Cr³⁺ Phosphors Emitting in the Second Near-Infrared Window

Extending emission into the NIR-II window (>1000 nm) would enable deeper tissue penetration with reduced scattering, but such emission is exceedingly rare, with only six materials previously reported. Finding new Cr³⁺ phosphors is challenging because the emission maximum (λ_em) and full width at half-maximum (fwhm) are highly sensitive to host composition, crystal structure, and local coordination environment, making them hard to predict in advance.

Here, we present a data-driven framework for identifying Cr³⁺ phosphors and apply it to find two new NIR-II-emitting materials, LiInW₂O₈ and NaScW₂O₈, with broadband emission centered at 1085 and 1100 nm, respectively, and a third NIR-I emitter, Ba₂ScTaO₆, centered at 890 nm. This effort required building a data set of 208 experimentally reported Cr³⁺ phosphor spectra using an automated literature-extraction pipeline and training two CatBoost regression models to independently predict λ_em and fwhm.