Nanocrystal (NC) self-assembly is a versatile platform for materials engineering at the mesoscale. The NC shape anisotropy leads to structures not observed with spherical NCs. This work presents a broad structural diversity in multicomponent, long-range ordered superlattices (SLs) comprising highly luminescent cubic CsPbBr 3 NCs (and FAPbBr 3 NCs) coassembled with the spherical, truncated cuboid, and disk-shaped NC building blocks. CsPbBr 3 nanocubes combined with Fe 3 O 4 or NaGdF 4 spheres and truncated cuboid PbS NCs form binary SLs of six structure types with high packing density; namely, AB 2 , quasi-ternary ABO 3 , and ABO 6 types as well as previously known NaCl, AlB 2 , and CuAu types. In these structures, nanocubes preserve orientational coherence. Combining nanocubes with large and thick NaGdF 4 nanodisks results in the orthorhombic SL resembling CaC 2 structure with pairs of CsPbBr 3 NCs on one lattice site. Also, we implement two substrate-free methods of SL formation. Oil-in-oil templated assembly results in the formation of binary supraparticles. Self-assembly at the liquid–air interface from the drying solution cast over the glyceryl triacetate as subphase yields extended thin films of SLs. Collective electronic states arise at low temperatures from the dense, periodic packing of NCs, observed as sharp red-shifted bands at 6 K in the photoluminescence and absorption spectra and persisting up to 200 K.

Lead halide perovskite nanocrystals (NCs) were recently found to exhibit extraordinary optical amplification properties. The great majority of such studies implemented ultrashort photon pulses in the femtosecond regime to initiate the stimulated emission process. Yet the realization of practical lasing applications based on such materials is crucially dependent on their ability to sustain optical amplification at significantly longer time scales, at which major losses associated with spontaneous emission and nonradiative recombination occur. Herein we demonstrate highly efficient amplified spontaneous emission (ASE) from close-packed films of formamidinium lead iodide perovskite (FAPbI3) NCs under excitation in the nanosecond regime. Systematic optimization of the NC processing and thermal treatment yields solids that exhibit high ASE net modal gain up to 604 cm–1 and weakly temperature sensitive ASE thresholds with room-temperature values as low as 140 μJ cm–2. The efficient optical amplification using excitation pulses comparable to the exciton lifetime combined with the excellent chemical durability and air stability of FAPbI3 NCs renders them outstanding gain media for continuous-wave lasers in the red and near-infrared.

Advances in the technology and processing of flexible optical materials have paved the way toward the integration of semiconductor emitters and polymers into functional light emitting fabrics. Lead halide perovskite nanocrystals appear as highly suitable optical sensitizers for such polymer fiber emitters due to their ease of fabrication, versatile solution-processing and highly efficient, tunable, and narrow emission across the visible spectrum. A beneficial byproduct of the nanocrystal incorporation into the polymer matrix is that it provides a facile and low-cost method to chemically and structurally stabilize the perovskite nanocrystals under ambient conditions. Herein, we demonstrate two types of robust fiber composites based on electrospun hydrophobic poly(methyl methacrylate) (PMMA) or hydrophilic polyvinylpyrrolidone (PVP) fibrous membranes sensitized by green-emitting all-inorganic CsPbBr 3 or hybrid organic-inorganic FAPbBr 3 nanocrystals. We perform a systematic investigation on the influence of the nanocrystal-polymer relative content on the structural and optical properties of the fiber nanocomposites and we find that within a wide content range, the nanocrystals retain their narrow and high quantum yield emission upon incorporation into the polymer fibers. Quenching of the radiative recombination at the higher/lower bound of the nanocrystal:polymer mass ratio probed is discussed in terms of nanocrystal clustering/ligand desorption due to dilution effects, respectively. The nanocomposite's optical stability over an extended exposure in air and upon immersion in water is also discussed. The studies confirm the demonstration of robust and bright polymer-fiber emitters with promising applications in backlighting for LCD displays and textile-based light emitting devices.

Solution-processed lasers are cost-effective, compatible with a vast range of photonic resonators, and suited for a mass production of flexible, lightweight, and disposable devices. The emerging class of lead halide perovskite nanocrystals (LHP NCs) can serve as a highly suitable active medium for such lasers, owing to their outstanding optical gain properties and the suppressed optical nonradiative recombination losses stemming from their defect-tolerant nature. In this work, CsPbBr 3 NCs are embedded within polymeric Bragg reflectors to produce fully solution-processed microcavities. By a systematic parametric optimization of the polymer mirrors, resonators with Q-factors up to 110 can be produced in the green, supporting amplified spontaneous emission (ASE) under continuous wave excitation, with a threshold as low as 140 mW/cm 2 . Angle-dependent reflectivity and luminescence studies performed below the ASE threshold demonstrate the strong spectral and angular redistribution of the CsPbBr 3 NC spontaneous emission when coupled to the cavity mode. Under resonance, amplification of the output intensity by a factor of 9 in the vicinity of the cavity mode and by a factor of 5 in the whole integrated emission along with an increase of the radiative rate accounted by a Purcell factor of 2 is obtained with respect to NCs deposited in reference microcavity structures.

The primary obstacle to the use of lead halide perovskite nanocrystals (NCs) in optoelectronics is the inability of traditional ligand engineering approaches to provide robust surface passivation. The structural lability can be mitigated by employing different ligands such as long-chain quaternary ammonium and zwitterionic surfactants. Here, we report a comprehensive study that probes the impact of such surface passivation routes on the optoelectronic properties of weakly confined CsPbBr 3 NCs. Spectroscopy unravels clear correlations of various photophysical figures of merit with the ligand type used. Compared to NCs decorated by conventional oleic acid/oleylamine ligands, passivation with the quaternary ammonium or zwitterionic surfactants increases the NC solid-state emission yield by up to 40% by halving the average trap depth and increasing by 1.5 times the exciton binding energy. Furthermore, the aforementioned ligands better preserve the size of NCs in thin films, as shown by the absence of significant NC aggregation and the confinement-induced increase by a factor of 2 of the Froḧlich interaction between excitons and optical phonons. The suitability of ligands for photonics is finally assessed by probing metrics, such as the amplified spontaneous emission threshold, the moisture tolerance, and the photoconductivity and electroluminescent performance of lateral and vertical devices, respectively.