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, Sb3+ (5s2) with the lone-pair electron configuration and In3+ (4d10) with the fully-filled electron configuration. (Me2NH2)4MCl6<middle dot>Cl (Me = -CH3, M = Sb, In) exhibits the superior temperature/component-dependent luminescence behaviors resulting from the competition transition between triplet-states (Tn-S0) self-trapped excitons (STEs) of inorganic units and singlet-state (S1-S0) of organic cations, which is manipulated by the optical activity levels of [SbCl6]3- and [InCl6]3-. The bonding differences between Sb3+/In3+ 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 Sb3+/In3+ alloying, the photoluminescence quantum yield (PLQY = 81.5%) and stability are optimized at 20% alloying of Sb3+. 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. (Me2NH2)4MCl6<middle dot>Cl (M = Sb, In) exhibits the superior temperature/component-dependent luminescence behaviors resulting from the competition transition between the triplet-states (Tn-S0) STEs of inorganic units and the singlet-state (S1-S0) of organic cations, which is manipulated by the optical activity levels of [SbCl6]3- and [InCl6]3-. This work sheds light on the different electron-transition mechanisms, as well as explores the optical-functional applications such as temperature sensors and anti-counterfeiting. image