NaYS2:Er3+ - a highly efficient NIR II response multi-photon up-conversion phosphor

The second near-infrared (NIR II) response photon up-conversion (UC) materials show great application prospects in the fields of biology and optical communication. However, it is still an enormous challenge to obtain efficient NIR II response materials. Herein, we developed a series of Er3+ doping ternary sulfides phosphors with highly efficient UC emissions under 1532 nm irradiation. Excitingly, β-NaYS2:Er3+ achieves a breakthrough visible UC efficiency as high as 6.13%, along with outstanding brightness, spectral stability of lights illumination and temperature. Such efficient UC dominates by excited state absorption process accompanied by the advantage of super long lifetimes of excited state levels of Er3+, instead of the well-recognized energy transfer UC between sensitizer and activator. NaYS2:Er3+ phosphors are further developed for high-performance underwater communication and a narrowband NIR photodetectors. Our findings breakthrough the traditional thinking of realizing efficient UC, and open up a novel frontier for developing NIR II response UC materials.