Polarized emission from semiconductor lead-halide perovskite nanocrystals

Semiconductor lead-halide perovskite nanocrystals (NCs) have recently emerged as one of the leading fluorescent materials, owing to their high fluorescence quantum yield, large absorption coefficient, tunable bandgap energy, and good defect tolerance. Unique features of the optical emissions from perovskite NCs are their high brightness and narrow linewidth with multifarious linear and circular polarization patterns. Directly connected to the microscopic wavefunctions, quantum numbers, and optical selection rules of the exciton states, these polarization patterns are susceptible to electric and magnetic fields, and amenable to the NC size, geometry, and surrounding environment. As such, they can be utilized to accurately probe and manipulate the exciton populations, spin polarizations, and spin-dependent many-body interactions of perovskite NCs, promising novel quantum and spintronic applications such as entangled photon sources and spin light-emitting diodes. In this article, we survey recent experimental progress made in the room- and cryogenic-temperature optical studies of linearly and circularly polarized emissions in perovskite NCs, elucidate the microscopic origins and underlying physics, and evaluate existing strategies to control and manipulate these polarizations. We also bring up key challenges in this nascent field and share our perspectives on a set of future research directions that exploit the polarized emission of perovskite NCs, aiming to spawn new opportunities for their use in both classical optoelectronic devices and emerging quantum information technology.