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Layered hybrid organic–inorganic metal‐halide perovskites (HOIPs) can acquire chirality from molecules incorporated into their structure showing exciting possibilities in optoelectronics and spintronics. However, researchers have focused their attention on the study of bulk compounds, namely unstable and toxic Pb HOIPs. Herein, the chiroptical properties of R‐ and S‐β‐methylphenethylammonium Mn chloride HOIPs are reported in both the bulk and the few‐layer limit as exfoliated flakes. Red photoluminescence (PL) emission originating from the octahedrally coordinated Mn2+ is observed, with a PL shift to longer wavelengths when passing from bulk to flakes. Circular dichroism and circularly polarized PL mirrored‐signals for enantiomers are found in bulk samples, while in flakes, a degree of circularly polarized emission (P) of up to 17% at 80 K is achieved, comparable to Pb‐based HOIPs. Moreover, angle‐resolved PL measurements on flakes show that the PL emission and P are isotropic. These findings highlight the potential of these HOIPs from bulk to flakes for spin‐optoelectronic applications. [ABSTRACT FROM AUTHOR]

Germanium–tin (GeSn) microdisks are promising structures for complementary metal–oxide–semiconductor‐compatible lasing. Their emission properties depend on Sn concentration, strain, and operating temperature. Critically, the band structure of the alloy varies along the disk due to different lattice deformations associated with mechanical constraints. An experimental and numerical study of Ge1−xSnx microdisk with Sn concentration between 8.5 and 14 at% is reported. Combining finite element method calculations, micro‐Raman and X‐ray diffraction spectroscopy enables a comprehensive understanding of mechanical deformation, where computational predictions are experimentally validated, leading to a robust model and insight into the strain landscape. Through micro‐photoluminescence experiments, the temperature dependence of the bandgap of Ge1−xSnx is parametrized using the Varshni formula with respect to strain and Sn content. These results are the input for spatially dependent band structure calculations based on deformation potential theory. It is observed that Sn content and temperature have comparable effects on the bandgap, yielding a decrease of more than 20 meV for an increase of 1 at% or 100 K, respectively. The impact of the strain gradient is also analyzed. These findings correlate structural properties to emission wavelength and spectral width of microdisk lasers, thus demonstrating the importance of material‐related consideration on the design of optoelectronic microstructures. [ABSTRACT FROM AUTHOR]

Understanding the structural and magnetic properties in layered hybrid organic‐inorganic metal halide perovskites (HOIPs) is key for their design and integration in spin‐electronic devices. Here, a systematic study is conducted on ten compounds to understand the effect of the transition metal (Cu2+, Mn2+, Co2+), organic spacer (alkyl‐ and aryl‐ammonium), and perovskite phase (Ruddlesden‐Popper and Dion‐Jacobson) on the properties of these materials. Temperature‐dependent Raman measurements show that the crystals' structural phase transitions are triggered by the motional freedom of the organic cations as well as by the flexibility of the inorganic metal‐halide lattice. In the case of Cu2+ HOIPs, an increase of the in‐plane anisotropy and a reduction of the octahedra interlayer distance is found to change the behavior of the HOIP from that of a 2D ferromagnet to that of a quasi‐3D antiferromagnet. Mn2+ HOIPs show inherent antiferromagnetic octahedra intralayer interactions and a phenomenologically rich magnetism, presenting spin‐canting, spin‐flop transitions, and metamagnetism controlled by the crystal anisotropy. Co2+ crystals with non‐linked tetrahedra show a dominant paramagnetic behavior irrespective of the organic spacer and the perovskite phase. This study demonstrates that the chemical flexibility of HOIPs can be exploited to develop novel layered magnetic materials with tailored magnetic properties. [ABSTRACT FROM AUTHOR]

Aerocelluloses are considered as “third generation” aerogels after the silica and synthetic polymer-based ones. However, their brittleness and low optical translucency keep quite narrow their fields of applications. Here, both issues are addressed successfully through the fabrication of flexible and mechanically robust amorphous aerocellulose with high optical transparency, using trifluoroacetic acid as a solvent and ethanol as a non-solvent. The developed aerocellulose displays a meso-macroporous interconnected nanofibrous cellulose skeleton with low density and high specific surface area. We demonstrate its high efficiency as supporting matrix for nanoscale systems by incorporating a variety of colloidal quatum dots, that provide bright and stable photoluminescence to the flexible aerocellulose host. [ABSTRACT FROM AUTHOR]

In the past few years, several protocols have been reported on the synthesis of CdSe nanoplatelets with narrow photoluminescence (PL) spectrum, high PL quantum efficiency, and short exciton lifetime. The corresponding core/shell nanoplatelets are however still mostly based on CdSe/CdS, which possess an extended lifetime and a strong red shift of the band-edge absorption and emission, in accordance with a quasi-type-II band alignment. Here we report on a robust synthesis procedure to grow a ZnS shell around CdSe nanoplatelets at moderate temperatures of 100-150 °C, to improve the optical properties of CdSe nanoplatelets via a type-I core/shell heterostructure. The shell growth is performed under ambient atmosphere, in either toluene or 1,2-dichlorobenzene. The variation of the shell thickness induces a continuous red shift of the PL peak, eventually reaching 611 nm. The PL quantum efficiency is increased compared to the original CdSe cores, with values up to 60% depending on the shell thickness. High-resolution transmission electron microscopy reveals a bending of the nanoplatelets caused by strain due to 12% lattice mismatch between CdSe and ZnS. The present procedure can easily be translated to other core/shell nanocrystals, such as CdSe/CdS and CdSe/CdZnS nanoplatelets. [ABSTRACT FROM AUTHOR]