Highly efficient tunable mid-infrared luminescence achieved by crystal field modulation of CsPb1-xHoxBr3 halide perovskite AlF3-based fluoride glass

Mid-infrared (MIR) light sources have gained significant importance across various applications in spectroscopy, sensing, astronomy, communications and medical surgery. The diverse spectral characteristics of rare earth ions, particularly lanthanide ions, stemming from their distinctive 4f intershell transitions, offer a multitude of potential transitions spanning the UV–visible–infrared spectrum. Despite recent advancements in MIR gain luminescence, the investigation of tunable MIR luminescence mechanisms remains a major technical challenge. Herein, an effective mechanism to modulate the local crystal field of rare earth ions by altering its crystal structure has been revealed, resulting in tunable broad-spectrum emission in the MIR luminescence range of 2800–3000 nm and multi-peak emission in the near-infrared band of Ho³⁺. Notably, the local crystal field of Ho³⁺ is adjusted by manipulating the lattice symmetry of CsPb_1-xHo_xBr₃ perovskite through the incorporation of fluoride glass reticulation to control the crystal size of the perovskite and thereby modify the lattice symmetry of CsPb_1-xHo_xBr₃ perovskite. The energy level transition of Ho³⁺ is influenced by adjusting the crystal field asymmetry, resulting in the splitting of the ⁵I₆ energy level depending on the crystal field. This cleavage affects the transitions from the ⁵I₅ level to ⁵I₆ at 1480 nm and from ⁵I₆ to ⁵I₇ at 2880 nm. As ⁵I₆ acts as the common upper level for the two emission peaks, the infrared peaks at 1480 nm and 2880 nm widen and develop into a dual-peak emission phenomenon. The infrared luminescence produced aligns closely with the distinctive infrared absorption peaks of carbon dioxide, leading to the development of a convenient, high-precision device for monitoring of CO₂ concentration in hydrogen energy in real time. These findings are anticipated to pave the way for extensive utilization of novel tunable MIR luminescence.