Dual-site occupation induced broadband near-infrared luminescence in SrHf4(PO4)6: Cr3+ toward emerging spectroscopic applications

Broadband near-infrared phosphor-converted LEDs (NIR pc-LEDs) are highly desirable for emerging spectroscopic applications. However, the simultaneous realization of long-wavelength emission and broad spectral coverage remains challenging. Herein, we report a novel Cr 3+ -activated phosphate phosphor SrHf 4 (PO 4 ) 6 : Cr 3+ that exhibits broadband NIR emission centered at 890 nm with a full width at half maximum of 162 nm under blue-light excitation. The red-shifted and broadened emission is enabled by a weak crystal-field environment and the dual-site occupation of Cr 3+ in the SrHf 4 (PO 4 ) 6 lattice. Structural analysis and electron paramagnetic resonance measurements indicate that Cr 3+ ions occupy both Sr 2+ and Hf 4+ sites, which is further supported by the emission-band deconvolution, wavelength-dependent lifetime analysis and formation-energy calculations. The thermal-quenching behavior is also investigated to clarify the non-radiative relaxation mechanism associated with electron-phonon coupling. Moreover, a prototype NIR pc-LED fabricated with the optimized phosphor delivers an output power of 57.4 mW and a photoelectric conversion efficiency of 5.1% at 350 mA, demonstrating its potential applications in non-destructive testing, information encryption and night-vision imaging. This work provides a structurally interpretable dual-site strategy for extending and broadening Cr 3+ NIR emission in phosphate hosts, offering guidance for the development of advanced broadband NIR light sources.