Efficient Near-Infrared Luminescence with Broad-Band Sensitization in Mo⁴⁺-Er³⁺ Co-Doped Cs₂ZrCl₆ Vacancy-Ordered...

Lanthanide (Ln³⁺)-doped lead-free inorganic metal halide perovskites with near-infrared (NIR) luminescence have shown great promise in optoelectronics. However, these materials exhibit low NIR efficiency due to insufficient absorption from forbidden f - f transitions. Herein, a strategy based on Mo⁴⁺-Er³⁺ co-doping is reported to achieve efficient NIR emission in Cs₂ZrCl₆ phosphors, which are excitable by low-cost multicolor light-emitting diode (LED) chips. Besides a broadband NIR emission of $d_{\mathrm{yz},\mathrm{zx}}\to d_{\mathrm{xy}}$ transition of Mo⁴⁺ ions centered at 960 nm, the co-doped sample also exhibits an NIR-II emission peak at 1543 nm. These Mo⁴⁺- Er³⁺ codoped samples achieved an overall photoluminescence quantum yield of 66.7%, with Er³⁺ emission contributing 8.3%. Mo⁴⁺ ions not only sensitize Er³⁺ ions but also possess broad-band excitation extending from ultraviolet to NIR region (250-850 nm). Further, temperature-dependent (10-400 K) steady state and time-resolved photoluminescence provide mechanistic information on excitation, emission, and sensitization mechanisms. These findings provide a general approach to achieve efficient NIR emission by codoping of optically active metal cations. The admirable stability and dual NIR bands of Mo⁴⁺-Er³⁺ co-doped Cs₂ZrCl₆ microcrystals will open new avenues for NIR light sources excitable by low-cost multicolor LED chips in potential optical communication, night-vision, and bio-imaging applications.