Monodisperse Long-Chain Sulfobetaine-Capped CsPbBr₃ Nanocrystals and Their Superfluorescent Assemblies

Abstract

Ligand-capped nanocrystals (NCs) of lead halide perovskites, foremost fully inorganic CsPbX3 NCs, are the latest generation of colloidal semiconductor quantum dots. They offer a set of compelling characteristicslarge absorption cross section, as well as narrow, fast, and efficient photoluminescence with long exciton coherence timesrendering them attractive for applications in light-emitting devices and quantum optics. Monodisperse and shape-uniform, broadly size-tunable, scalable, and robust NC samples are paramount for unveiling their basic photophysics, as well as for putting them into use. Thus far, no synthesis method fulfilling all these requirements has been reported. For instance, long-chain zwitterionic ligands impart the most durable surface coating, but at the expense of reduced size uniformity of the as-synthesized colloid. In this work, we demonstrate that size-selective precipitation of CsPbBr3 NCs coated with a long-chain sulfobetaine ligand, namely, 3-(N,N-dimethyloctadecylammonio)-propanesulfonate, yields monodisperse and sizable fractions (>100 mg inorganic mass) with the mean NC size adjustable in the range between 3.5 and 16 nm and emission peak wavelength between 479 and 518 nm. We find that all NCs exhibit an oblate cuboidal shape with the aspect ratio of 1.2 × 1.2 × 1. We present a theoretical model (effective mass/k·p) that accounts for the anisotropic NC shape and describes the size dependence of the first and second excitonic transition in absorption spectra and explains room-temperature exciton lifetimes. We also show that uniform zwitterion-capped NCs readily form long-range ordered superlattices upon solvent evaporation. In comparison to more conventional ligand systems (oleic acid and oleylamine), supercrystals of zwitterion-capped NCs exhibit larger domain sizes and lower mosaicity. Both kinds of supercrystals exhibit superfluorescence at cryogenic temperaturesaccelerated collective emission arising from the coherent coupling of the emitting dipoles.

Surface Functionalization of CsPbBr3 Νanocrystals for Photonic Applications

“…PL QY values above 80% have been reported for DDAB-and DDAB/PbBr 2 -capped CsPbBr 3 NCs, 15,37−39 while values approaching unity have been demonstrated in ZI-capped NCs. 6,36,40 Photophysics at Low Photoexcitation Densities. Exciton recombination in low photoexcitation conditions of exciton occupancy ⟨N⟩ ∼ 0.2 was probed via variable temperature PL experiments in the 10−340 K range; the raw data in the form of three-dimensional contour plots are presented in Figure 2a−d for the studied NC films.…”

“…At room temperature, average PL lifetimes of ∼7 ns have been obtained for the OA-, DDAB-, and ZI-capped NCs and ∼12 ns for the DDAB/PbBr 2 NCs, in agreement with the literature reported range, i.e., ∼6−12 ns for OA NCs, 7−14 ns for DDAB-based NCs, and ∼7 ns for ZIcapped NCs. 15,35,38,40,58,59 The validity of the rather arbitrary assignment of the radiative lifetime to the dominant PL decay term and the associated estimation of the radiative yield in the two studied NC systems are confirmed by (i) the reasonably good resemblance of the temperature variation of the integrating PL and the radiative QY displayed in Figure 3 and (ii) the good matching of the QY values computed at room temperature with those estimated via integrating sphere PL experiments (blue data points and error), discussed earlier in the text. For the DDAB-and DDAB/PbBr 2-capped NCs, the transient PL model requires three decay components; hence, the aforementioned reasoning for the estimation of the radiative lifetime and the QY cannot be applied.…”

Taming the nucleation and growth kinetics of lead halide perovskite quantum dots

“…They are much praised for simultaneously exhibiting near-unity PL quantum yields (QYs), a PL peak tailorable across the 410-800 nm spectral range with small PL full widths at half maximum (FWHM, ˂100 meV), largeabsorption cross-sections 26 , long exciton coherence times and sub-ns fast radiative rates at low temperatures [27][28][29] . Much scientific interest revolves around single-photon emission from LHP NCs 7,8,[29][30][31] and collective phenomena in LHP NC assemblies such as superfluorescence 9,[32][33][34] .…”

Highly Concentrated, Zwitterionic Ligand-Capped Mn2+:CsPb(BrxCl1–x)3 Nanocrystals as Bright Scintillators for Fast Neutron Imaging

“…Among colloidal nanocrystals, lead halide perovskite (LHP) NCs have recently emerged as the new benchmark. 17 − 19 Their unmatched optical properties, on both the single-particle 20 , 21 and ensemble 22 − 24 levels, promoted them as powerful candidates for a variety of applications spanning from LEDs for displays 25 − 28 to fluorescent NCs for lighting. 19 , 25 We recently demonstrated the proof of concept by using colloidal NCs as recoil proton detectors, with these transparent solutions offering light yield without any evidence of scattering or afterglow.…”