Hybrid
organic–inorganic perovskites demonstrate desirable
photophysical behaviors and promising applications from efficient
photovoltaics to lasing, but the fundamental nature of excited state
species is still under debate. We collected time-resolved photoluminescence
of single-crystal nanoplates of methylammonium lead iodide perovskite
(MAPbI3) with excitation over a range of fluences and repetition
rates to provide a more complete photophysical picture. A fundamentally
different way of simulating the photophysics is developed that relies
on unnormalized decays, global analysis over a large array of conditions,
and inclusion of steady-state behavior; these details are critical
to capturing observed behaviors. These additional constraints require
inclusion of spatially correlated pairs along with free carriers and
traps, demonstrating the importance of our comprehensive analysis.
Modeling geminate and nongeminate pathways shows that geminate processes
are dominant at high carrier densities and early times and that geminate
recombination is catalyzed by free holes. Our combination of data
and simulation provides a detailed picture of perovskite photophysics
across multiple excitation regimes that was not previously available.
Intrinsically disordered proteins, such as tau protein, adopt a variety of conformations in solution, complicating solution-phase structural studies. We employ an anti-Brownian electrokinetic (ABEL) trap to prolong measurements of single tau proteins in solution. Once trapped, we record the fluorescence anisotropy to investigate the diversity of conformations sampled by the single molecules. A distribution of anisotropy values obtained from trapped tau protein is conspicuously bimodal while those obtained by trapping a globular protein or individual fluorophores are not. Time-resolved fluorescence anisotropy measurements are used to provide an explanation of the bimodal distribution as originating from a shift in the compaction of the two different families of conformations.
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