Energy extraction from dark Fe3+ in A2Sc2B4O11:Fe3+, Yb3+ (A = Sr, Ba) toward promoted NIR luminescence and pc-LED light source for multifunctional applications

Abstract New generation of Cr 3+ -free eco-friendly phosphors (no risk of Cr 3+ → Cr 6+ oxidization toxicity) are highly sought to develop broadband NIR light sources. As an essential element for body health, Fe 3+ ion would be an exceptional alternative in strong octahedral crystal field. Here, the Fe 3+ activators were utilized in orthoborate-pyroborate A 2 Sc 2 B 4 O 11 for creating novel NIR-emitting phosphors. A broad absorption over 240–450 nm due to O 2- → Fe 3+ charge transfer transition was recorded for Sr 2 Sc 2 B 4 O 11 :Fe 3+ (SSBO:Fe 3+ ) at 370 nm and Ba 2 Sc 2 B 4 O 11 :Fe 3+ (BSBO:Fe 3+ ) at 355 nm. Resultant NIR emissions with large full width at half maximum about 170 nm were obtained for SSBO:Fe 3+ peaked at 975 nm and BSBO:Fe 3+ at 930 nm. The unique excitation of Fe 3+ doping towards near-ultraviolet (near-UV) region was initially achieved for potential advantage of coupling a mainstream UV chip. Codoping of Yb 3+ into A 2 Sc 2 B 4 O 11 :Fe 3+ made emission peak red-shift towards 1000 nm and ~ 160-fold enhancement in the integral intensity owing to a robust energy extraction from the major dark (nonluminous) Fe 3+ . The optimized SSBO:0.02Fe 3+ ,0.15Yb 3+ exhibited considerable internal and external quantum efficiency ~ 78% and 48%, respectively. Compared to the luminescence thermal stability of ASBO:Fe 3+ (32%@373 K, i.e., sustaining 32% of its room-temperature emission intensity at 373 K), the Yb 3+ codoping endowed much superior stability > 63%@373 K, and additional temperature sensing with relative sensitivity ~ 1.5% K −1 at 423 K. Ultimately, by coating the novel phosphors onto UV ~ 365 nm chips, the home-made pc-LEDs were applied in night vision, food inspection, biomedical imaging, and spectroscopy analysis.