We use single crystal CsPbBr 3 NWs grown from vapor deposition on sapphire substrates 28. The latter is unprecedented, and is strong evidence for stimulated emission from an n-EHP coupled with plasmon emission. Rather, the lasing spectrum under pulsed excitation is a strongly time-dependent function, which consists of red-shifting cavity modes concurrent with blue-shifting laser gain profiles. We find that the time-integrated laser emission spectra, typical in nearly all reports on LHP lasers published to date, obscure the intrinsic nonlinear physics in the system. We carry out complementary measurements through ultrafast transient reflectance. Here, we use ultrafast time-resolved photoluminescence (PL) to directly probe lasing dynamics in CsPbBr 3 perovskite NWs via spectral evolution with ~1 ps time resolution. While exciton-polaritons may exist at low excitation density and continuous wave (CW) conditions, lasing under pulsed excitation may occur above the exciton Mott density from stimulated emission from a non-degenerate electron hole plasma (n-EHP, also referred to as a Coulomb-correlated EHP) 24, 25, 26, 27. The formation of exciton-polaritons, a coherent superposition between an exciton and a photon in a microcavity, is well known in layered LHPs 21, 22, 23 and has been suggested as an underlying lasing mechanism in LHPs 16, 20. Various mechanisms have been proposed to explain the quantitative characteristics of lasing from NW or other microcavities of LHPs 1, 15, 16, 17, 18, 19, 20. Despite a plethora of publications on carrier dynamics 6, 7, 8, 9, 10, 11, 12, 13, 14 and lasing 1, 15, 16, 17, 18, 19, 20 in LHPs, it remains unclear how these two aspects are related.Ĭentral to the debate on the lasing mechanisms is the role of excitons. Photophysical studies in the past few years have established that charge carrier properties in LHPs are distinct from those in conventional semiconductors those in the former are exemplified by exceptional defect tolerance, slow hot carrier cooling, and efficient dynamic screening 6. Light emission with near unity quantum yield, low lasing thresholds, and compositionally tuneable wavelength makes them strong contenders for highly efficient light emitting devices, nanowire (NW) lasers, and potentially exciton-polariton devices 1, 2, 3, 4, 5. Lead halide perovskites (LHPs) continue to draw attention for their extraordinary photovoltaic efficiencies and their expanding roles in optoelectronic research.
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