Ligand-induced chirality in semiconductor nanocrystals (NCs) has attracted attention because of the tunable optical properties of the NCs. Induced circular dichroism (CD) has been observed in CdX (X = S, Se, Te) NCs and their hybrids, but circularly polarized luminescence (CPL) in these fluorescent nanomaterials has been seldom reported. Herein, we describe the successful preparation of l- and d-cysteine-capped CdSe-dot/CdS-rods (DRs) with tunable CD and CPL behaviors and a maximum anisotropic factor ( g) of 4.66 × 10. The observed CD and CPL activities are sensitive to the relative absorption ratio of the CdS shell to the CdSe core, suggesting that the anisotropic g-factors in both CD and CPL increase to some extent for a smaller shell-to-core absorption ratio. In addition, the molar ratio of chiral cysteine to the DRs is investigated. Instead of enhancing the chiral interactions between the chiral molecules and DRs, an excess of cysteine molecules in aqueous solution inhibits both the CD and CPL activities. Such chiral and emissive NCs provide an ideal platform for the rational design of semiconductor nanomaterials with chiroptical properties.

As an emerging type of optically active material, semiconductor nanocrystals (NCs) stabilized by chiral molecules have attracted much attention. Owing to the wide range of potential applications of chiral perovskite NCs, the development of these materials is of great importance, but there has been a lack of relevant studies. Here, we describe an investigation of the properties of chiral perovskite NCs obtained using post-synthetic ligand exchange (achiral ligand/chiral ligand). These are found to exhibit mirror-image circular dichroism spectra. It is the chirality of the ligand (enantiomeric 1,2-diaminocyclohexane, DACH) that is most likely responsible for the induction of chiroptical activity in these NCs. Furthermore, their chiroptical properties and the corresponding mechanisms are found to depend strongly on the amount of capping ligand. When excess DACH is used to cap the surface of the NCs, their chiroptical properties are induced mainly by aggregation of DACH on the surface in a chiral pattern. In contrast, when small amounts of DACH are used for the capping, it is mainly surface distortion (or defects) and electronic interaction mechanisms that contribute to the chiroptical behavior of the NCs. In both cases, the anisotropy factors of the NCs are of the order of 10−3, which is comparable to or larger than the values reported for other chiral semiconductor and metal NCs. This work opens the door toward further understanding of chiroptical perovskite NCs and their potential applications.

Ultrafast carrier dynamics in the topological insulator Bi2Se3 have been intensively studied using a variety of techniques. However, we are not aware of any successful experiments exploiting transient absorption (TA) spectroscopy for these purposes. Here we demonstrate that if the ~730 nm wavelength pumping (~1.7 eV photon energy) is applied to ultrathin Bi2Se3 films, the TA spectra cover the entire visible region, thus unambiguously pointing to two-photon excitation (~3.4 eV). The carrier relaxation dynamics is found to be exclusively influenced by whether the Dirac point is presented between the Dirac cones of the higher energy (~1.5 eV) surface states (known as SS2). We recognized that SS2 act as a valve substantially slowing down the relaxation of carriers when the gap between the Dirac cones exceeds the phonon and resonant defects energies. The progressive accumulation of carriers in the gapped SS2 becomes detectable through the inverse bremsstrahlung type free carrier absorption.

We constructed an intelligent cloud lab that integrates lab automation with cloud servers and artificial intelligence (AI) to detect chirality in perovskites. Driven by the materials acceleration operating system in cloud (MAOSIC) platform, on-demand experimental design by remote users was enabled in this cloud lab. By employing artificial intelligence of things (AIoT) technology, synthesis, characterization, and parameter optimization can be autonomously achieved. Through the remote collaboration of researchers, optically active inorganic perovskite nanocrystals (IPNCs) were first synthesized with temperature-dependent circular dichroism (CD) and inversion control. The inter-structure (structural patterns) and intrastructure (screw dislocations) dual-pattern-induced mechanisms detected by MAOSIC were comprehensively investigated, and offline theoretical analysis revealed the thermodynamic mechanism inside the materials. This self-driving cloud lab enables efficient and reliable collaborations across the world, reduces the setup costs of in-house facilities, combines offline theoretic analysis, and is practical for accelerating the speed of material discovery.

Hybrid organic–inorganic metal halides have emerged as highly promising materials for a wide range of applications in optoelectronics. Incorporating chiral organic molecules into metal halides enables the extension of their unique optical and electronic properties to chiral optics. By using chiral (R)‐ or (S)‐methylbenzylamine (R‐/S‐MBA) as the organic component, we synthesized chiral hybrid copper halides, (R‐/S‐MBA)2CuCl4, and investigated their optical activity. Thin films of this material showed a record anisotropic g‐factor as high as approximately 0.06. We discuss the origin of the giant optical activity observed in (R‐/S‐MBA)2CuCl4 by theoretical modeling based on density functional theory (DFT) and demonstrate highly efficient second harmonic generation (SHG) in these samples. Our study provides insight into the design of chiral materials by structural engineering, creating a new platform for chiral and nonlinear photonic device applications of the chiral hybrid copper halides.

Nonlinear optical effects in layered two-dimensional transition metal chalcogenides have been extensively explored recently because of the promising prospect of the nonlinear optical effects for various optoelectronic applications. However, these materials possess sizable bandgaps ranging from visible to ultraviolet region, so the investigation of narrow-bandgap materials remains deficient. Here, we report our comprehensive study on the nonlinear optical processes in palladium diselenide (PdSe2) that has a near-infrared bandgap. Interestingly, this material exhibits a unique thickness-dependent second harmonic generation feature, which is in contrast to other transition metal chalcogenides. Furthermore, the two-photon absorption coefficients of 1–3 layer PdSe2 (β ~ 4.16 × 105, 2.58 × 105, and 1.51 × 105 cm GW−1) are larger by two and three orders of magnitude than that of the conventional two-dimensional materials, and giant modulation depths (αs ~ 32%, 27%, and 24%) were obtained in 1–3 layer PdSe2. Such unique nonlinear optical characteristics make PdSe2 a potential candidate for technological innovations in nonlinear optoelectronic devices.

All-inorganic lead halides, including CsPbX3 (X = Cl, Br, I), have become important candidate materials in the field of optoelectronics. However, the inherent toxicity of metal lead and poor material...

The dynamic and static Rashba effects in hybrid methylammonium (MA) lead halide perovskites have recently been theoretically predicted. However, only the static effect was experimentally confirmed so far. Here, we report on the dynamic (sub-picosecond/picosecond timescale) and static (nanosecond/microsecond timescale) Rashba effects observed in a fully encapsulated layer with various thicknesses (ranging from ∼40 nm to ∼100 nm) of ∼20-nm-sized 3D MAPbBr3 nanocrystals (NCs) using transient absorption (TA) spectroscopy. The effect appears as a splitting of the corresponding peaks in TA spectra. We argue that the physical reason for the Rashba effect to be observed is fundamentally determined by configurational entropy loss in NCs possessing a strong spin asymmetry. Specifically, owing to an enhanced flexibility of the NC lattice, a built-in electric field initially induced by an ultrashort (100 fs) pumping pulse through the photo-Dember effect and subsequently developed due to dynamic charge separation throughout NCs is able to initiate the order–disorder transition associated with the MA cation reorientations, the process that efficiently breaks structural inversion symmetry and hence induces the Rashba spin–orbit interaction. The dynamic Rashba effect is found to be strongly dependent on photoexcited carrier density (pumping power), whereas it weakens sharply upon increasing the NC layer thickness up to ∼80 nm due to the NC stacking effect. The integrated intensities of the corresponding spin-split subbands demonstrate a photon-helicity-dependent asymmetry, thus proving the Rashba-type spin-splitting. The magnitudes of the Rashba and Fröhlich polaron effects and the methods of controlling the dynamic Rashba effect are discussed.