Efficient broad-band NIR-II emitting phosphor Mg4Ta2O9: Ni2+ with satisfactory thermal stability of luminescence

The applications of near-infrared (NIR) spectroscopy in the fields of medicine and food safety require efficient and compact NIR light sources, for example, NIR phosphor converted light-emitting diodes (pc-LEDs). In recent years, Ni2+ has become one of the main activators for its broadband NIR-II (1000–1700 nm) emission under ultraviolet or visible light excitation. However, two important effects (Concentration quenching which decreases the emission intensity and temperature quenching which decreases the adaptability of phosphor in high-power applications) seriously hinder the development of Ni2+ doped NIR-II emitting phosphors. It is an urgent and important task to restrain both concentration and thermal quenching of the Ni2+ luminescence to develop an efficient NIR-II emitting phosphor. Here, novel NIR-II emitting Mg4Ta2O9: Ni2+ phosphors with perovskite-like structure were synthesized and investigated. In Mg4Ta2O9, the quenching concentration of Ni2+ is as high as 0.045. This is a relatively high value for Ni2+ activated NIR-II emitting phosphors. Mg4Ta2O9: 0.045Ni2+ presents broadband emission (1100–1700 nm, the full width at half maximum (FWHM) = 218 nm) with internal and external quantum efficiency of 64.2% (IQE) and 7.2% (EQE), respectively. The phosphor exhibits excellent luminous thermal stability (at 423 K, it keeps 84.85% of initial intensity at room temperature). High structure stiffness of Mg4Ta2O9 is responsible for the high quenching concentration and desirable luminous thermal stability. This work developed an efficient NIR-II emitting phosphor which exhibits desirable thermal stability of luminescence. Theoretically, this work points out a direction for future development of efficient NIR-II emitting phosphors, selecting an inorganic compound with high structural rigidity as the host for Ni2+ doping.