We present the easy and high yield synthesis of several group 13 MesDPM compounds (Al-In) with alkyl substituents at the metal atom. All these compounds were fully characterized using techniques including X-ray diffraction analysis and photoluminescence measurements. It shows that for aluminium and gallium pronounced green fluorescence is observed, which is absent for indium. DFT calculations confirm that the first electronic transition corresponds to a ligand-based pi-pi* transition. An easy and high yield synthesis of several higher homologues of BODIPY with the elements aluminium, gallium and indium is presented. It shows that for aluminium and gallium pronounced green fluorescence appears.

Two-dimensional (2D) materials exhibit the potential to transform semiconductor technology. Their rich compositional and stacking varieties allow tailoring materials' properties toward device applications. Monolayer to multilayer gallium sulfide (GaS) with its ultraviolet band gap, which can be tuned by varying the layer number, holds promise for solar-blind photodiodes and light-emitting diodes as applications. However, achieving commercial viability requires wafer-scale integration, contrasting with established, limited methods such as mechanical exfoliation. Here the one-step synthesis of 2D GaS is introduced via metal-organic chemical vapor deposition on sapphire substrates. The pulsed-mode deposition of industry-standard precursors promotes 2D growth by inhibiting the vapor phase and on-surface pre-reactions. The interface chemistry with the growth of a Ga adlayer that results in an epitaxial relationship is revealed. Probing structure and composition validate thin-film quality and 2D nature with the possibility to control the thickness by the number of GaS pulses. The results highlight the adaptability of established growth facilities for producing atomically thin to multilayered 2D semiconductor materials, paving the way for practical applications. Two-dimensional gallium sulfide (2D GaS) emitting in the ultraviolet to visible spectral range is synthesized via metal-organic chemical vapor deposition. Pulsed deposition of industry-standard precursors promotes 2D growth. The interface chemistry with the growth of a Ga adlayer as well as strain relation upon the growth of thicker layers resulting in an epitaxial relationship is revealed. Thickness control is enabled by tuning the number of GaS pulses. image

Two-dimensional (2D) materials are gaining great attention due to their extraordinary thickness-dependent properties. 2D Ga-VI semiconductors have bandgaps in the UV region making them candidates for several LED concepts. The Indium-containing counterparts of Ga-chalcogenides moreover have small electron effective masses and high mobilities. Hence, 2D III-chalcogenides are promising materials for next-generation optoelectronic applications. We establish metal organic chemical vapor deposition (MOCVD) to find suitable growth routines for 2D materials. We will summarize our current understanding of the MOCVD growth of III-chalcogenides by systematic variation of the growth parameters and correlate the findings to optoelectronic properties of the layers.

Lead halide perovskites and related main-group halogenido metalates offer unique semiconductor properties and diverse applications in photovoltaics, solid-state lighting, and photocatalysis. Recent advances in incorporating chiral organic cations have led to the emergence of chiral metal-halide semiconductors with intriguing properties, such as chiroptical activity and chirality-induced spin selectivity, enabling the generation and detection of circularly polarized light and spin-polarized electrons for applications in spintronics and quantum information. However, understanding the structural origin of chiroptical activity remains challenging due to macroscopic factors and experimental limitations. In this work, we present an achiral perovskite derivative [Cu2(pyz)3(MeCN)2][Bi3I11] (CuBiI; pyz = pyrazine; MeCN = acetonitrile), which exhibits remarkable circular dichroism (CD) attributed to the material's noncentrosymmetric nature. CuBiI features a unique structure as a poly-threaded iodido bismuthate, with [Bi3I11]2- chains threaded through a cationic two-dimensional coordination polymer. The material possesses a low, direct optical band gap of 1.70 eV. Notably, single crystals display both linear and circular optical activity with a large anisotropy factor of up to 0.16. Surprisingly, despite the absence of chiral building blocks, CuBiI exhibits a significant degree of circularly polarized photoluminescence, reaching 4.9%. This value is comparable to the results achieved by incorporating chiral organic molecules into perovskites, typically ranging from 3-10% at zero magnetic field. Our findings provide insights into the macroscopic origin of CD and offer design guidelines for the development of materials with high chiroptical activity.

The second and third order nonlinear susceptibilities of the ferroelectric oxides LiNbO$_3$, LiTaO$_3$, and KNbO$_3$ are calculated from first principles. Two distinct methodologies are compared, one approach is based on a perturbative approach within the frequency-domain, another on the time-evolution of the electric polarization. The frequency dependence of the second harmonic coefficients of the ferroelectric phase of LiNbO$_3$ calculated within the two approaches is in excellent agreement. This is further validated by experimental data for LiNbO$_3$ and LiTaO$_3$, measured for an incident range of photon energies between 0.78 eV and 1.6 eV. The real-time based approach is furthermore employed to estimate the third order nonlinear susceptibilities of all investigated ferroelectric oxides. We further show that the quasiparticle effects, considered by means of a scissors-shift in combination with the the computationally efficient independent particle approximation, result in a shift all spectral features towards higher energies and decrease the magnitude of the optical nonlinearities. The energy of the main resonances in the hyperpolarizabilities suggests that the spectra can be understood by multi-photon adsorption within the fundamental bandgap for all investigated materials.

Functionalized adamantane molecular cluster materials show highly transient nonlinear optical properties of currently unclear structural origin. Several interaction mechanisms in compounds comprising molecular clusters, their inter- and intramolecular interactions as well as the interplay of their electronic systems and vibrations of their backbone are viable concepts to explain these nonlinear optical properties. We show that transient Coulomb forces also have to be considered as they can lead to intramolecular structure transformations and intermolecular rearrangements in the crystal. Both strongly influence the nonlinear optical properties. Moreover, selective bromine functionalization can trigger a photochemical rearrangement of the molecules. The structure and chemical bonding within the compounds are investigated in dependence on the laser irradiation at different stages of their nonlinear emission by electron diffraction and electron energy loss spectroscopy. The transient structural and chemical states observed are benchmarked by similar observations during electron irradiation, which makes quantification of structural changes possible and allows the correlation with first principles calculations. The functionalization and its subsequent usage to exploit photochemical effects can either enhance two-photon absorption or facilitate white-light emission rather than second-harmonic generation.

The efficient light-matter interaction of molecular materials renders them prime candidates for (electro-)optical devices or as nonlinear optical media. In particular, white-light generation is highly desirable for applications ranging from illumination to metrology. In this respect, cluster compounds have gained significant attention as they can show highly brilliant white-light emission. The actual microscopic origin of the optical nonlinearity, however, remains unclear and requires in-depth investigations. Here, we select the family of group 14 tetraphenyl tetrels with chemical formula X(C6H5)(4) and X = C, Si, Ge, Sn, and Pb as the model system, and we study the properties of single molecules and molecular crystals. Calculations in the framework of the density functional theory yield the structural, vibrational, and electronic properties, electronic excitations, linear optical absorption, as well as second- and third-order optical susceptibilities. All well agree with the experimentally determined structural and vibrational properties, as well as the linear and nonlinear optical responses of specifically grown crystalline [X(C6H5)(4)] samples with X = Si, Ge, Sn, and Pb. This thorough characterization of the compounds yields deep insight into this material class on the path toward understanding the origin of the characteristic white-light emission.

Sustainable efficient light emitters based solely on elements-of-hope are needed to replace current compounds based on less-abundant materials. Functionalized diamondoids are a potential solution for this challenge, as a prototypical example offers efficient, octave-spanning emission across the visible spectrum in their single-crystalline form. Its large quantum efficiency increases towards higher-than-ambient temperatures to beyond 7%. The stability beyond 200 °C renders such functionalized diamondoids as sustainable phosphors for LED applications. Detailed structural and theoretical investigations suggest a crucial role of exciton states accompanied by structural modifications (self-trapped excitons) in the emission process.

Amorphous materials are an integral part of today's technology-they commonly are performant and versatile in integration. Consequently, future applications increasingly aim to harvest the potential of the amorphous state. Establishing its structure-property relationship, however, is inherently challenging using diffraction-based techniques yet is extremely desirable for developing advanced functionalities. In this article, we introduce a set of transmission electron microscopy-based techniques to locally quantify the structure of a material. This unique approach allows to clearly identify the spatial distribution of amorphous and crystalline regions and to quantify atomic arrangements of amorphous regions of a representative model system. We study an ensemble of well-defined, functionalized adamantane-type cluster molecules exhibiting exceptionally promising nonlinear optical properties of unclear origin. The nanoscopic structure for three model compounds ([(PhSn)(4)S-6], [(NpSn)(4)S-6], [(CpSn)(4)S-6]) correlates with their characteristic optical responses. These results highlight the advantageous properties of amorphous molecular materials when understanding the microscopic origin.