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

 https://doi.org/10.1002/adfm.202401860

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·Cl (Me = −CH₃, M = Sb, In) exhibits the superior temperature/component-dependent luminescence behaviors resulting from the competition transition between triplet-states (T_n-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.