Relaxing Cr3+ Site-Occupation Constraints to Enable Ultrawideband Emission Covering NIR-I and NIR-II

Near-infrared (NIR) luminescence capable of covering NIR-I and NIR-II is highly promising for biomedical imaging and non-invasive inspection. However, achieving both broadband and long-wavelength emission remains challenging due to the activator ion site-occupation constraints. In this work, we report La 3 TiGa 5 O 14 :Cr 3+ (LTG:Cr 3+ ) phosphor that exhibits an ultrawideband NIR emission spanning the spectral range of 650–1400 nm. The underlying mechanism involves Ti and Ga site exchange, which triggers local polyhedral reorganization. This structural transformation creates a weak crystal field, large Stokes shift, lower energy barrier of activator ion site occupancy, and more sites favorable for Cr 3+ incorporation ─ collectively relaxing Cr 3+ site-occupation constraints. The optimized LTG:0.03Cr 3+ phosphor exhibits NIR emission at 1017 nm with an exceptionally broad full width at half maximum (FWHM) of 476 nm. Moreover, introducing Ta 5+ as a charge-compensating dopant boosts NIR emission intensity by nearly 3.9-fold. A prototype NIR LED device fabricated with this phosphor demonstrates effective multi-channel signal detection. This work advances site-occupancy engineering from extrinsic doping to intrinsic polyhedral reorganization, providing a molecular design framework for high-performance NIR phosphor.