Achieving Flat Ultra-Broadband NIR Emission in Cr3+ Doped Garnet-Type Phosphors Enabled by Structural Regulation Toward Multi-Functional Spectroscopy Applications

Cr3+-activated near-infrared (NIR) emitting phosphors are considered as one of the most potential light-conversion materials for NIR phosphor converted light-emitting diodes (NIR pc-LEDs). However, it is still a challenge for a single Cr3+ ion to achieve a flat ultra-broadband emission toward multi-functional spectroscopy applications. Herein, a chemical unit co-substituting strategy is utilized to regulate the crystallographic occupancy of Cr3+ ions, and a flat ultra-broadband NIR emission is successfully realized with a record emission wavelength of 915 nm in garnet-type phosphors Ca3Sc2-xHfxAlxSi3-xO12: yCr(3+) (0 <= x <= 1, 0.02 <= y <= 0.06), together with a large full width at half maximum (FWHM) regulation from 130 to 250 nm. The relation between the site occupation of Cr3+ ions in disordered [CaO8], [(Sc, Hf)O-6] and [(Si, Al)O-4] polyhedrons and the corresponding NIR emission are clarified by carefully evaluating the structural evolution, Raman spectra, electron paramagnetic resonance and time-resolved emission lifetime spectra of Cr3+ ions. The corresponding crystal field strength of Cr3+ ions is investigated to further clarify the multi-sites induced flat broadband NIR emission. Finally, a blue light pumped NIR pc-LED is fabricated with a total output power of 37.58 mW and photoelectric conversion efficiency (PCE) of 13.67%@100 mA, which realizes the multi-functional applications in night vision imaging, non-destructive detection and palmprint vein recognition for assistant medical treatment.