Single crystal Cr3+-doped NIR phosphor: enhanced luminescence intensity and improved thermal stability†

Single crystals of Cr³⁺-doped guanidine-based organic–inorganic hybrid fluorides (GA₃GaF₆:Cr³⁺) with sizes up to 6 × 5 × 2 mm³ were successfully synthesized using a facile room-temperature solvent exchange crystallization method. The GA₃GaF₆:Cr³⁺ single crystal exhibits near-infrared (NIR) emission centered at 802 nm with a full width at half-maximum (FWHM) of 130 nm upon blue light excitation. Compared to polycrystalline powders, the GA₃GaF₆:Cr³⁺ single crystal demonstrates enhanced luminescence intensity and improved thermal stability. Notably, the bright green GA₃GaF₆:Cr³⁺ single crystal maintains its structural integrity at temperatures up to 540 K without degradation and retains over 75% of its initial luminescence intensity at 373 K. Furthermore, the GA₃GaF₆:Cr³⁺ single crystals exhibit excellent environmental stability, preserving 77% of their initial luminescence intensity after exposure to high temperature and high humidity (85 °C, 85% RH) for 5 days. This work represents a significant advancement in the development of organic–inorganic hybrid fluoride single-crystal materials for near-infrared emitting devices.