Zero-thermal-quenching broadband NIR-II emitting Mg4Nb2O9: Ni2+ phosphor via defective engineering and multi-site occupation

Developing phosphor-converted light-emitting diodes (pc-LEDs) for portable near-infrared (NIR) spectroscopy applications has generated significant demand for NIR-II phosphors. However, developing a NIR-II phosphor with both broadband emission and good thermal stability remains a significant challenge. Herein, we report a novel Ni 2+ -doped Mg 4 Nb 2 O 9 (MNO) phosphor that exhibits a full-width at half maximum (FWHM) of 213 nm, covering a wavelength range of 1100–1700 nm, with a peak at 1319 nm when excited by 405 nm ultraviolet (UV) light. The optimized phosphor exhibited an internal quantum efficiency (IQE) of 38.31 %. By combining first-principles calculations with experimental analysis, we established that Ni 2+ ions occupy the three octahedral cation sites in the MNO host. Notably, the MNO: 0.004Ni 2+ phosphor maintains 102 % of its initial emission intensity at 423 K compared to room temperature (RT), exhibiting a zero-thermal-quenching property, which can be attributed to the thermal energy transfer from oxygen vacancy defects to activator ions, large thermal energy barrier, as well as the high rigidity of the MNO host. An NIR-II pc-LED device was constructed by encapsulating the optimized phosphor within a UV LED chip. The application of nondestructive NIR spectroscopy in detection, night vision, and bioimaging further demonstrates the potential of this device.