2 research outputs found
Purcell Enhancement and Wavelength Shift of Emitted Light by CsPbI3 Perovskite Nanocrystals Coupled to Hyperbolic Metamaterials
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
Delayed Luminescence in Lead Halide Perovskite Nanocrystals
The
mechanism responsible for the extremely long photoluminescence (PL)
lifetimes observed in many lead halide perovskites is still under
debate. While the presence of trap states is widely accepted, the
process of electron detrapping back to the emissive state has been
mostly ignored, especially from deep traps as these are typically
associated with nonradiative recombination. Here, we study the photophysics
of methylammonium lead bromide perovskite nanocrystals (PNCs) with
a photoluminescence quantum yield close to unity. We show that the
lifetime of the spontaneous radiative recombination in PNCs is as
short as 2 ns, which is expected considering the direct bandgap character
of perovskites. All longer (up to microseconds) PL decay components
result from the rapid reversible processes of multiple trapping and
detrapping of carriers with a slow release of the excitation energy
through the spontaneous emission channel. As our modeling shows, the
trap (dark) and excitonic states are coupled by the trapping–detrapping
processes so that they follow the same population decay kinetics,
while a majority of excited carriers are in the dark state. The lifetime
of the PNCs delayed luminescence is found to be determined by the
depth of the trap states, lying from a few tens to hundreds meV below
the emitting excitonic state. The delayed luminescence model proposed
in this work can serve as a basis for the interpretation of other
photoinduced transient phenomena observed in lead halide perovskites