One of distinguishing features of metal halide perovskites is their long (up to microseconds) photoluminescence (PL) lifetimes, which are regularly observed for this class of semiconductors in spite of their direct gap origin. It is difficult to explain this contradiction in the framework of usual two-level Jablonski photophysical diagram because the absorption coefficient (i.e., the oscillator strength of the direct optical transition) is too high in perovskites to hold such long PL lifetimes. In this paper, we describe practical steps how the PL decay kinetics of perovskites in the forms of (1) passivated nanocrystals and (2) thin multicrystalline films can be described. In case of nanocrystals, the three-level delayed luminescence model is described by including shallow non-quenching traps providing multiple trapping and de-trapping of carriers and thus essentially lengthening the observed PL lifetime. In the case of perovskite thin films limited by interfacial recombination, the PL decay kinetics is usually determined by the non-radiative recombination on the film surfaces and can be satisfactorily described in terms of one-dimensional diffusion equation. The limits of applicability of such approaches are discussed.

Manipulation of the exciton emission rate in nanocrystals of lead halide perovskites (LHPs) was demonstrated by means of coupling of excitons with a hyperbolic metamaterial (HMM) consisting of alternating thin metal (Ag) and dielectric (LiF) layers. Such a coupling is found to induce an increase of the exciton radiative recombination rate by more than a factor of three due to the Purcell effect when the distance between the quantum emitter and HMM is nominally as small as 10 nm, which coincides well with the results of our theoretical analysis. Besides, an effect of the coupling-induced long wavelength shift of the exciton emission spectrum is detected and modeled. These results can be of interest for quantum information applications of single emitters on the basis of perovskite nanocrystals with high photon emission rates.

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