Ultra-broadband near-infrared emission of AlNbO4:Cr3+ transparent glass-ceramics

Abstract

Broadband near-infrared (NIR) light has wide applications in the fields of deep-tissue imaging, photodynamic therapy and industrial inspection. NIR pc-LED is regarded as a promising solution for high-performance NIR light sources due to its spectral tunability and compact design. However, the low absorption and poor chemical stability caused by a high scattering of phosphors and organic encapsulation, limit the further applications. In this study, a novel pure Cr³⁺-doped AlNbO₄ transparent glass-ceramics (GCs) was prepared via a heat-treated (HT) technique. As the HT temperature increased from 820 °C to 900 °C, the crystallinity, crystal size and luminous intensity increase gradually, while the transmittance decrease in turn. Cr³⁺ preferentially substitutes for Al³⁺ sites and occupies octahedral coordination centers in AlNbO₄ phase. The GC exhibits a high transmittance over 60 % and a high absorptivity of 80.1 % at a HT temperature of 900 °C. An ultra-broadband NIR emission (650-1400 nm) was obtained with a peak wavelength of 870 nm and a full width at half maximum (FWHM) of 237 nm under excitation at 442 nm. The GCs show an intermediate crystal field environment (Dq/B ≈ 2.3), which indicates an intermediate electron-phonon coupling and leads to a broadband NIR light. The GCs show an external quantum efficiency (EQE) of 17.7 % and a thermal-quenching resistance of 55.7 % initial intensity at 348 K. The optimized NIR LED device fabricated with AlNbO₄:Cr³⁺ GC demonstrates a significant application potential in the fields of non-destructive security inspection and biomedical imaging.