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

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.