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UiO-66 is a Zr-based metal-organic framework (MOF) with exceptional chemical and thermal stability. The modular design of a MOF allows the tuning of its electronic and optical properties to obtain tailored materials for optical applications. Making use of the halogenation of the 1,4-benzenedicarboxylate (bdc) linker, the well-known monohalogenated UiO-66 derivatives were examined. In addition, a novel diiodo bdc based UiO-66 analogue is introduced. The novel UiO-66-I2 MOF is fully characterized experimentally. By applying density functional theory (DFT), fully relaxed periodic structures of the halogenated UiO-66 derivatives are generated. Subsequently, the HSE06 hybrid DFT functional is used to calculate the electronic structures and optical properties. The obtained band gap energies are validated with UV-Vis measurements to assure a precise description of the optical properties. Finally, the calculated refractive index dispersion curves are evaluated underlining the capabilities to tailor the optical properties of MOFs by linker functionalization.

Dimensionality is the game-changer property of a material. The optical and electronic properties of a compound get dramatically influenced by confining dimensions from 3D to 2D. The bulk 3D perovskite materials have shown remarkable up-gradation in the power conversion efficiency, hence grabbing worldwide attention. But instability against moisture, temperature, and ion migration are the factors constantly back-stabbing and hindering from full-scale commercialization. 2D perovskite material has emerged as an excellent bridging entity between structural-chemical stability, and viable commercialization. Organic-inorganic 2D perovskite materials come with a layered structure in which a large organic cation layer as a spacer is sandwiched between two inorganic metal halide octahedra layers. Moreover, hydrophobic spacer cations are employed which isolate inorganic octahedral layers from water molecules. Hydrophobic spacer cations protect the authentic structure from being degraded. These layered structures occur in two phases namely the Ruddlesden-Popper phase and Dion-Jacobson phase, depending on the spacer cation types. Alternating inorganic and organic layers form multiple quantum wells naturally, along with spin-orbit-coupling gives Rashba splitting. 2D perovskite materials are coming up with interesting chemical, physical properties like exciton dynamics, charge carrier transport, and electron-phonon coupling as a result of the quantum confinement effect. Despite appreciable stability, limited charge transport and large bandgap are limiting the application of 2D perovskite materials in solar cells. These limitations can be overcome by using the concept of 2D/3D multidimensional hybrid perovskites, which includes the long-term stability of 2D perovskite and the high performance of 3D perovskite at the same time. Here in this perspective, we have given brief insight on structural versatility, synthesis techniques, some of the unique photophysical properties, potential

In this paper, we systematically investigate the structural, mechanical, optical and electronic properties of novel two-dimensional XY (X = Al, Ga, In; Y = N, P, As) monolayers in the double layer hexagonal structure (DLHS) using first-principles calculations. Our calculations show that single-layers of XY are stable, with the exception of GaP monolayer, which is unstable with its phonon spectrum containing negative frequencies. Also, the linear elastic parameters confirm the Born conditions for mechanical stability of XY monolayers and they are brittle structures. Most XY monolayers have indirect semiconductor characteristics with band gaps of 3.54 eV, 1.78 eV, 0.18 eV, 1.68 eV and 1.28 eV for AlN, GaN, InN, AlP, and AlAs monolayers. However the GaAs monolayer has a metallic character. The optical results indicate the InN and AlAs monolayers have ability to absorb the visible light spectra. We expect that our findings will point the way forward for the use of these structures in microelectronics and optoelectronics devices.

In this paper, we systematically investigate the structural, mechanical, optical and electronic properties of novel two-dimensional XY (X = Al, Ga, In; Y = N, P, As) monolayers in the double layer hexagonal structure (DLHS) using first-principles calculations. Our calculations show that single-layers of XY are stable, with the exception of GaP monolayer, which is unstable with its phonon spectrum containing negative frequencies. Also, the linear elastic parameters confirm the Born conditions for mechanical stability of XY monolayers and they are brittle structures. Most XY monolayers have indirect semiconductor characteristics with band gaps of 3.54 eV, 1.78 eV, 0.18 eV, 1.68 eV and 1.28 eV for AlN, GaN, InN, AlP, and AlAs monolayers. However the GaAs monolayer has a metallic character. The optical results indicate the InN and AlAs monolayers have ability to absorb the visible light spectra. We expect that our findings will point the way forward for the use of these structures in microelectronics and optoelectronics devices.

Recent development in two-dimensional materials is due to their exceptional performances in the field of electronics and optical devices in the nano regime. First principles investigation based on density functional theory is used to predict the existence of Li2O in two-dimensional hexagonal monolayer flatlands. Li2O is found to be in H- and T-phase honeycomb structures in monolayer regime. The structural stability was confirmed by phonon calculation which suggests their potential experimental realization. The mechanical properties of both Hand T-phases of Li2O is calculated, the in-plane stiffness of both phases are 10.56% and 15.77% of graphene whereas the Poisson ratio for both phases are more than 1.5 times that of graphene. The electronic band structure calculation reveals that H phase of Li2O is metallic in nature, while the T phase exhibits direct band gap of 2.87 eV. Further, the optical properties for both H and T phases of Li2O suggests their potential applications in optical devices. Present results enlighten that this new two-dimensional Li2O can be utilized to develop stable and efficient optoelectronic materials.

W18O49 has been studied by means of ab initio techniques in the framework of the density functional theory using the onsite Hubbard-U correction applied to the W-d states as well as using the hybrid potential. The existence of bipolarons is found to be an intrinsic feature of this oxide resulting in the presence of different oxidation states of W atoms (W6+ and W5+) and in the co-existence of localized and delocalized electrons. We also discuss possible switching from the W6+ to W5+ and from the W5+ to W4+ oxidation states in the presence of an O vacancy. It appears that O vacancy formation does not cause any additional charge localization at W sites but solely contributes to delocalized electrons. The calculated absorption and reflection coefficients manifest a transparency window in the visible region. At the same time, sizable absorption, occurring due to the presence of free carriers, is detected in the far and mid infrared regions. Additionally, in the near infrared region we confirm and explain an experimentally observed shielding effect originating from transitions involving the localized bipolaronic states., QC 20220613

In this work, we study the electronic, optical, and photocatalytic properties of fully hydrogenated GeC monolayer under strain engineering and external electric field using first-principles investigations. Our calculations demonstrate that at the equilibrium state, fully hydrogenated GeC monolayer is a indirect-semiconductor with band gap of 3.493 eV and it possesses photocatalytic characteristics for water splitting and in particular, photocatalytic activities can be enhanced by a negative electric field under ultraviolet light. We can control the band gap of fully hydrogenated GeC monolayer by biaxial strain or external electric field and semiconductor–metal phase transition happens at certain elongation of biaxial strain. Compared to pure monolayer GeC, the fully hydrogenation causes optical absorption peaks of GeC shifting to a higher energy region. While the optical spectra of the fully hydrogenated GeC monolayer are strongly dependent on the strain, the effect of the electric field on them is negligible. Our findings can provide useful information for the applicability of fully hydrogenated GeC monolayer in nanoelectronic devices and photocatalytic water splitting.In this work, we study the electronic, optical, and photocatalytic properties of fully hydrogenated GeC monolayer under strain engineering and external electric field using first-principles investigations. Our calculations demonstrate that at the equilibrium state, fully hydrogenated GeC monolayer is a indirect-semiconductor with band gap of 3.493 eV and it possesses photocatalytic characteristics for water splitting and in particular, photocatalytic activities can be enhanced by a negative electric field under ultraviolet light. We can control the band gap of fully hydrogenated GeC monolayer by biaxial strain or external electric field and semiconductor–metal phase transition happens at certain elongation of biaxial strain. Compared to pure monolayer GeC, the fully hydrogenation causes optical absor

In this work, we study the electronic, optical, and photocatalytic properties of fully hydrogenated GeC monolayer under strain engineering and external electric field using first-principles investigations. Our calculations demonstrate that at the equilibrium state, fully hydrogenated GeC monolayer is a indirect-semiconductor with band gap of 3.493 eV and it possesses photocatalytic characteristics for water splitting and in particular, photocatalytic activities can be enhanced by a negative electric field under ultraviolet light. We can control the band gap of fully hydrogenated GeC monolayer by biaxial strain or external electric field and semiconductor–metal phase transition happens at certain elongation of biaxial strain. Compared to pure monolayer GeC, the fully hydrogenation causes optical absorption peaks of GeC shifting to a higher energy region. While the optical spectra of the fully hydrogenated GeC monolayer are strongly dependent on the strain, the effect of the electric field on them is negligible. Our findings can provide useful information for the applicability of fully hydrogenated GeC monolayer in nanoelectronic devices and photocatalytic water splitting.In this work, we study the electronic, optical, and photocatalytic properties of fully hydrogenated GeC monolayer under strain engineering and external electric field using first-principles investigations. Our calculations demonstrate that at the equilibrium state, fully hydrogenated GeC monolayer is a indirect-semiconductor with band gap of 3.493 eV and it possesses photocatalytic characteristics for water splitting and in particular, photocatalytic activities can be enhanced by a negative electric field under ultraviolet light. We can control the band gap of fully hydrogenated GeC monolayer by biaxial strain or external electric field and semiconductor–metal phase transition happens at certain elongation of biaxial strain. Compared to pure monolayer GeC, the fully hydrogenation causes optical absor

In the present work, we have studied the electronic, optical, and thermoelectric properties of a monolayer of pristine HfS2 and two types of vacancy and two types of dopant by using first-principles calculations. These configurations with single atom vacancy (Hf and S atoms) and single atom dopant in place of a sulfur atom are energetically more favorable. The electronic properties of HfS2 monolayer are significantly affected by vacancies as well as dopants. Also, it transforms indirect-band-gap semiconducting behavior to direct-band-gap semiconducting behavior and semiconductor-to-metal HfS2 occurs during the structural defect. The variation in the work function of HfS2 monolayer by vacancy, as well as dopant, indicates the change in conductivity. The structural defect enhancing the light absorption as well as the conductivity of HfS2 monolayer and H-phase of it is suitable for UV light absorption while the T-phase is suitable for visible light absorption. From the thermoelectric properties, the relatively high Seebeck coefficient and it is found to be 2867 and 2902 mu V K-1 for doped P atom in the T-phase and the pristine H-phase, respectively, at room temperature. The figure of merit (ZT) at 300 K is determined to be 1 for the T-phase and 1.05 for the H-phase, while, at a higher temperature, ZT = 1.23 for the Hf vacancy in the T-phase. Such analysis reveals that the structural defects not only significantly affect the electronic properties, but they also can be used as an efficient way to modulate the thermoelectric properties and enhance ZT. The theoretical results suggest that the two-dimensional HfS2 monolayer is very useful in high-performance optoelectronic and thermoelectric devices.

In the present work, we have studied the electronic, optical, and thermoelectric properties of a monolayer of pristine HfS2 and two types of vacancy and two types of dopant by using first-principles calculations. These configurations with single atom vacancy (Hf and S atoms) and single atom dopant in place of a sulfur atom are energetically more favorable. The electronic properties of HfS2 monolayer are significantly affected by vacancies as well as dopants. Also, it transforms indirect-band-gap semiconducting behavior to direct-band-gap semiconducting behavior and semiconductor-to-metal HfS2 occurs during the structural defect. The variation in the work function of HfS2 monolayer by vacancy, as well as dopant, indicates the change in conductivity. The structural defect enhancing the light absorption as well as the conductivity of HfS2 monolayer and H-phase of it is suitable for UV light absorption while the T-phase is suitable for visible light absorption. From the thermoelectric properties, the relatively high Seebeck coefficient and it is found to be 2867 and 2902 mu V K-1 for doped P atom in the T-phase and the pristine H-phase, respectively, at room temperature. The figure of merit (ZT) at 300 K is determined to be 1 for the T-phase and 1.05 for the H-phase, while, at a higher temperature, ZT = 1.23 for the Hf vacancy in the T-phase. Such analysis reveals that the structural defects not only significantly affect the electronic properties, but they also can be used as an efficient way to modulate the thermoelectric properties and enhance ZT. The theoretical results suggest that the two-dimensional HfS2 monolayer is very useful in high-performance optoelectronic and thermoelectric devices., QC 20191014

The physical properties of polycrystalline HoRhGe have been studied experimentally and theoretically. The compound orders antiferromagnetically with a Néel temperature (TN) of 5.5K. It shows a large negative magnetoresistance (MR) of 25% at TN, for a field of 50kOe. However, at 2K and in lower fields, the MR is found to be positive with a magnitude of about 12%. The magnetocaloric effect has been estimated from both magnetization and heat capacity data and found to be large compared to many potential refrigerant materials in the same temperature range. The optical conductivity calculated theoretically from the ab initio results is in agreement with experimental values. The electronic structure calculations with the LSDA+U method accounting for the strong electronic correlations in the 4f shell of holmium show that the Ho 4f electronic states play a major role in determining its magnetic, electronic and optical properties. © 2014 IOP Publishing Ltd.

Very recently, Cu3BiS3 has been suggested as an alternative material for photovoltaic (PV) thin-film technologies. In this work, we analyze the electronic and optical properties of Cu3BiY 3 with the anion elements Y = S, Se, and Te, employing a first-principles approach within the density function theory. We find that the three Cu2BiY3 compounds have indirect band gaps and the gap energies are in the region of 1.2-1.7 eV. The energy dispersions of the lowest conduction bands are small, and therefore the direct gap energies are only ∼0.1 eV larger than the fundamental gap energies. The flat conduction bands are explained by the presence of localized Bi p-states in the band gap region. Flat energy dispersion implies a large optical absorption, and the calculations reveal that the absorption coefficient of Cu3BiY 3 is larger than 105 cm-1 for photon energies of ∼2.5 eV. The absorption is stronger than other Cu-S based materials like CuInS2 and Cu2ZnSnS4. Thereby, Cu 3BiY3 has the potential to be a suitable material in thin-film PV technologies., QC 20140114