Broadband Near-Infrared Luminescence from Mo4+ in Zero-Dimensional Perovskite Cs2Zr(Cl,Br)6 with an Exceptionally High Quantum Efficiency and Thermal Stability

Broadband near-infrared (NIR) luminescent materials hold the key to next-generation, smart, NIR light sources. The emerging halide perovskite materials are regarded as promising candidates for optoelectronics because of their superior optical properties and easy solution processability. However, it remains a major challenge to realize efficient and thermally stable broadband NIR luminescence in these materials. Herein, we report a novel strategy to achieve broadband NIR luminescence by utilizing the transitions from the lowest 1T2 level of Mo4+ to the components of its 3T1 ground state in the soft Cs2Zr(Cl,Br)6 lattice. The multiple transitions, each occurring within the (4d2) t22 crystal-field configuration and containing zero-phonon and vibronic contributions, superimpose on each other to generate the broadband NIR emission. The emission spectrum encompasses the long wavelength region from 800 to 1400 nm centered at 970 nm with a full width at half-maximum of 170 nm. More importantly, the title NIR phosphor shows an exceptional quantum efficiency (66.9%) and thermal stability (67%@150 °C). The as-fabricated NIR phosphor-converted light-emitting diode shows great potential as an NIR lighting source. This research opens a new horizon for realizing high-performance broadband NIR luminescence by exploiting multiple electronic transitions of activators in the soft lattice.