Interfacial Photophysics and Solvent-triggered Phase Reconstruction in Cs4PbBr6 Quantum Dots for Optical/Electrical Dual-Mode Sensing.

While all-inorganic lead halide perovskite quantum dots offer tunable pathways toward programmable optoelectronics, the origin of stimulus-activated phase transformation and its underlying photophysics remain controversial. Here, by constructing a composition-tunable dual-phase Cs4PbBr6-CsPbBr3 quantum dots platform with direct interfacial contact, we have identified key factors that regulate the emission behavior through careful structural and spectroscopic analyses, including interfacial strain and localized-states-induced changes of carrier trapping and recombination pathways. Furthermore, in situ solvent treatment uncovers the hydroxyl-triggered, polarity-modulated CsBr extraction mechanism that drives the localized conversion from non-emissive Cs4PbBr6 to green emissive CsPbBr3. Such solvent-programmable optical activation is further converted into an optical/electrical dual-mode readout using a planar photoconductor. The dual-mode response enables discrimination between hydroxyl-containing and hydroxyl-free solvents, identification of various protic solvents, and semi-quantitative analysis of water content in ethanol-water mixtures. This work provides synthetic and mechanistic strategies for regulating the structure-property relationships of interphase perovskite quantum dots and establishes a dual-mode sensing platform that couple photoluminescence activation with photoconductive signatures for solvent identification and discrimination.