Observation of Quasi-Invariant Photocarrier Lifetimes in PbS Nanocrystal Assemblies Coupled to Resonant and Nonresonant Arrays of Optical Antennas

We examine, in the time domain, the influence of Au antenna arrays (i.e., metasurfaces) on thin films of near-infrared PbS nanocrystals that mutually interact via Fo''rster resonance energy transfer (FRET). While the geometry and optical properties of the arrays have a direct and sometimes spectacular impact on the transient photoluminescence spectra of the emitters, we experimentally show that the decay rates at any given wavelength are remarkably similar for all samples. This observation is in stark contrast with the textbook case of individual emitters weakly coupled to photonic structures. We show that FRET plays two key roles in these experiments-first, it is more efficient than other nonradiative energy transfers, including Joule dissipation in the optical antennas, for most wavelengths; second, it thermalizes the photocarriers of neighboring nanocrystals before their recombination, making them behave as an effective semiconducting material obeying a generalized form of Kirchhoff's law.