Bright Blue-Emitting Hybrid Bimetallic Halides: Enabling Highly Sensitive Remote Thermometry via Swift Luminescent Response

Fluorescence lifetime thermometry is used for noncontact temperature sensing applications. However, conventional materials are limited by low luminescence efficiency and thermal sensitivity. Herein, we synthesized a series of Zn and alkaline earth ( Ae ) metal based bimetallic halides, Ae ( L ) 6 ZnBr 4 ( Ae = Ca, Sr; L = tetramethyl-urea (TMU) or dimethyl-propylene-urea (DMPU)), exhibiting blue emission upon UV excitation. Based on systematic optical characterizations and theoretical calculations, we revealed that the blue emission originates from the radiative recombination of singlet states of [ Ae ( L ) 6 ] 2+ complexes and self-trapped excitons, accompanied by an energy transfer process from [ Ae ( L ) 6 ] 2+ to [ZnBr 4 ] 2– . Altering the ligand from TMU to DMPU can suppress phonon-assisted nonradiative recombination, resulting in increased enhancement in quantum yields (up to 64.3% for Sr(DMPU) 6 ZnBr 4 ). The luminescence mechanism involving multiple photophysical processes of these hybrids offers suitable temperature sensitivity for lifetime thermometers. The composite film based on Sr(DMPU) 6 ZnBr 4 achieves a relative sensitivity of 9.66% K –1, along with excellent stability during repeated heating–cooling cycles. This work provides a viable strategy for developing high-efficiency blue-light emitters and underscores the potential of Zn-based bimetallic halides for high-sensitivity remote thermometry.