Temperature/Component‐Dependent Luminescence in Lead‐Free Hybrid Metal Halides for Temperature Sensor and Anti‐Counterfeiting

Abstract Hybrid metal halides (HMHs) have emerged as a promising platform for optically functional crystalline materials, but it is extremely challenging to thoroughly elucidate the electron transition coupled to additional ligand emission. Herein, to discover sequences of lead‐free HMHs with distinct optically active metal cations are aimed, that is, Sb 3+ (5s 2 ) with the lone‐pair electron configuration and In 3+ (4d 10 ) with the fully‐filled electron configuration. (Me 2 NH 2 ) 4 M Cl 6 ·Cl (Me = −CH 3 , M = Sb, In) exhibits the superior temperature/component‐dependent luminescence behaviors resulting from the competition transition between triplet‐states (T n ‐S 0 ) self‐trapped excitons (STEs) of inorganic units and singlet‐state (S 1 ‐S 0 ) of organic cations, which is manipulated by the optical activity levels of [SbCl 6 ] 3− and [InCl 6 ] 3− . The bonding differences between Sb 3+ /In 3+ and Cl − in terms of electronic excitation and hybridization are emphasized, and the different electron‐transition mechanisms are established according to the PL spectra at the extreme temperature of 5 to 305 K and theoretical calculations. By fine‐tuning the B‐site Sb 3+ /In 3+ alloying, the photoluminescence quantum yield (PLQY = 81.5%) and stability are optimized at 20% alloying of Sb 3+ . This research sheds light on the rules governing PL behaviors of HMHs, as well as exploring the optical‐functional application of aviation temperature sensors and access‐control systems.