Visualizing energy transfer across a hexagonal Cs₄PbBr₆ microdisk using single-particle spectroscopy

Micron-scale hexagonal Cs₄PbBr₆ perovskite microdisks (MDs), comprising a zero-dimensional phase, act as efficient energy donors when interfaced with the organic dye 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine-perchlorate (DiIC₁₈). Upon dye binding and selective excitation of the MDs, efficient singlet energy transfer (ET) occurs, as evidenced by the quenching of MD photoluminescence (PL), enhanced dye emission, and the emergence of an ET-induced rise component in the dye lifetime profile. Single-particle measurements under donor-selective excitation show strong ET-induced donor-acceptor PL anticorrelation, marked by a pronounced zero-delay dip [g²(0)] in the antibunching cross-correlation. Additional evidence for ET comes from single-particle PL trajectory analysis showing strong temporal correlation between donor and acceptor signals, and from simultaneous donor/acceptor-channel imaging under donor-only excitation, where spatially colocalized MD images confirm ET-mediated excitation of dye molecules distributed all over the MDs. Solution-phase ensemble measurements demonstrate relatively high ET efficiency (>50%) even at low bulk dye concentrations (∼1 µM). Spatially-resolved analysis further reveals ∼55% higher ET efficiency at the MD core compared to the edges, indicating preferential dye accumulation within the cavities located mostly in the core region. These results demonstrate that Cs₄PbBr₆ MDs serve as efficient ET platforms with tunable ET efficiency, providing promising potential for applications in photocatalysis, sensing, and light-harvesting technologies.