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The recently discovered phenomenon of broadband white-light emission at room temperature in the (110) two-dimensional organic-inorganic perovskite (N-MEDA)PbBr4 (N-MEDA = N(1)-methylethane-1,2-diammonium) is promising for applications in solid-state lighting. However, the spectral broadening mechanism and, in particular, the processes and dynamics associated with the emissive species are still unclear. Herein, we apply a suite of ultrafast spectroscopic probes to measure the primary events directly following photoexcitation, which allows us to resolve the evolution of light-induced emissive states associated with white-light emission at femtosecond resolution. Terahertz spectra show fast free carrier trapping and transient absorption spectra show the formation of self-trapped excitons on femtosecond time-scales. Emission-wavelength-dependent dynamics of the self-trapped exciton luminescence are observed, indicative of an energy distribution of photogenerated emissive states in the perovskite. Our results are consistent with photogenerated carriers self-trapped in a deformable lattice due to strong electron-phonon coupling, where permanent lattice defects and correlated self-trapped states lend further inhomogeneity to the excited-state potential energy surface.
Hu et al. (Wed,) studied this question.