Turning Self-Trapped Exciton Emission to Near-Infrared Region in Thermochromism Zero-Dimensional Hybrid Metal Halides

Low dimensional lead-free metal halides have become the spotlight of the research on developing multifunctional optoelectronic materials as their properties show a wide range of tunability. However, most reported low dimensional metal halides only function in the ultra-violet to visible range due to their large bandgap. Moreover, the organic cation based low dimensional metal halides show limited thermal stability; on the other hand, their inorganic cation based counterparts suffer from limited solution processability. A hybrid cation approach is proposed, where a zero dimensional (0D) metal halide ((DFPD)(2)CsBiI6) is developed by using mixed organic-inorganic cations: 4, 4-difluoropiperidine (DFPD) and cesium (Cs+). This ensures both thermal stability and solution processability. Furthermore, [BiI6](3-) octahedra are serving as active light absorption units, which ensures the bandgap to be located at the visible region. Its photoluminescence (PL) is further shifted to the near infrared (NIR) region by doping (DFPD)(2)CsBiI6 with antimony (Sb3+). The developed materials show multifunctional properties: thermochromic behavior, light detection, and NIR light emitting. This study expands the scope of developing multifunctional 0D metal halides.