Light–Matter Interaction and Lasing in Lead Halide Perovskites

Abstract

CONSPECTUS: Lead halide perovskites (LHPs) are attractive material systems for light emission, thanks to the ease and diverse routes of synthesis, the broad tunability in color, the high emission quantum efficiencies, and the strong light−matter coupling which may potentially lead to excitonpolariton condensation. This account contrasts the laser-like coherent light emission from highly lossy Fabry−Perot cavities, formed naturally from LHP nanowires (NWs) and nanoplates (NPs), with highly reflective cavities made of LHP gain media, sandwiched between two distributed Bragg reflector (DBR) mirrors. The mechanism responsible for the operation of conventional semiconductor lasers involves stimulated emission of electron and hole pairs bound by the Coulomb potential, i.e., excitons or, at excitation density above the so-called Mott threshold, an electron−hole plasma (EHP). We discuss how lasing from LHP NWs or NPs likely originates from stimulated emission of an EHP, not excitons or exciton-polaritons. A character central to this kind of lasing is the dynamically changing photonic properties in the naturally formed cavity. In contrast to the more static conditions of a DBR cavity, lasing modes and gain profiles are extremely sensitive to material properties and excitation conditions in an NW/NP cavity. While such unstable photonic cavities pose engineering challenges in the application of NW/NP lasers, they provide excellent probes of many-body physics in the LHP material. For sufficiently strong light−matter coupling expected for LHPs in DBR cavities, an exciton-polariton, i.e., the superposition state between the exciton and the cavity photon, can form. An exciting prospect of strong light−matter coupling is the potential formation of an exciton polariton condensate, which possesses many interesting quantum and nonlinear effects, such as superfluidity, long-range coherence, and laserlike light emission. However, it is difficult to distinguish coherent light from an exciton-polariton condensate and that from conventional stimulated laser emission. Several reports have established the condition of strong coupling for LHPs in DBR cavities. We stress, however, that these studies have not included necessary experiments to unambiguously establish the formation of exciton-polariton condensation, and several experiments and routes of analysis are needed to make a more convincing case for exciton-polariton condensation in LHP based systems. The potential of exciton-polariton condensation expands the horizon of LHP materials from conventional optoelectronics to quantum devices.

Observation of Two Thresholds Leading to Polariton Condensation in 2D Hybrid Perovskites

“…Moreover, polariton lasing and condensation have been described by Su et al [ 25,26 ] in 3D CsPbX 3 perovskites, although exciton‐polariton condensation in 2D perovskite has never been observed before. As pointed out by Schlaus et al, [ 27 ] it is not trivial to unambiguously distinguish polariton condensation from lasing emission in materials with multiple exciton levels, such as in lead halide perovskites, due to the presence of competitive population/depopulation kinetics.…”

Carrier Dynamics and Evaluation of Lasing Actions in Halide Perovskites

“…loss (c usually in the range of 10 -26 to 10 -29 cm 6 s -1 ) [35,40,41]. Lasing physics centering around materials engineering, structure modulation, and light-matter interaction has been systematically reviewed elsewhere [62,63]. In this section, we aim to provide a general view to identify lasing actions through carrier dynamics analysis.…”

Strongly Coupled Systems for Nonlinear Optics

“…In 1986, Rempe et al spotted the first strong light-matter interaction of single Rydbery atom in the microcavity. [31] Subsequently, as the relevant technologies and devices have matured, a massive of more complex molecules other than single atoms [27,84,85] have certified the existence of strong light-matter interaction in the cavities. A common feature that the transmission spectra of twolevel atoms split into double individual peaks has been validated in these strongly coupled systems.…”