Ion Substitution Strategy toward High-Efficiency Near-Infrared Photoluminescence of Cs2KIn1–yAlyF6:Cr3+ Solid Solutions

The rising demand for portable near-infrared (NIR) light sources has accelerated the exploration of NIR luminescent materials with high efficiency and excellent thermal stability. Inspired by the structural-modulated ion substitution strategy, herein, a high-performance Cs2KIn0.8Al0.1F6:0.1Cr3+ phosphor with a peak at 794 nm and full width at half-maximum (fwhm) of 117 nm was successfully synthesized by introducing Al3+ ions. The high performance is reflected in its high internal quantum efficiency (IQE) of 88.06% and good thermal quenching resistance (I423K = 71.64%). Compared with the initial Cs2KInF6:0.1Cr3+, the IQE and thermal stability are improved by 16.67% and 72.54%, which stem from the enhanced crystallinity and the strengthened structural rigidity. Finally, a phosphor-converted light-emitting diode (pc-LED) with a superior NIR photoelectric efficiency (21.04%@320 mA) was fabricated. Meanwhile, the pupil tracking, anticounterfeiting, intelligent identification, and bioimaging were successfully demonstrated. This work provides new perspectives for synthesizing efficient NIR fluoride phosphors and designing diverse applications.