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In this paper, a CSVO3 phosphor for white LED has been successfully prepared by solid-state synthesis and has been characterized. The CsVO3 was simulated by Materials Studio software based on density functional theory (DFT). The results show that the CsVO3 sample has a direct optical transition with band gap energy of 3.143 eV. Under ultraviolet excitation in the range of 300–390 nm, the emission spectrum of CsVO3 phosphors ranges from 400 to 700 nm, and its peak emission spectrum is near 492 nm, and shows yellow color fluorescence emission. These results indicate that CsVO3 phosphor can be used as a promising white phosphor for white LED. [ABSTRACT FROM AUTHOR]

In the present paper, we have investigated the electronic structure of some sillenites - Bi12MO20 (M = Ti, Ge, and Si) compounds based on the density functional theory. The mechanical and optical properties of Bi12MO20 have also been computed. The second-order elastic constants have been calculated, and the other related quantities have also been estimated in the present work. The band gap trend in Bi12MO20 can be understood from the nature of their electronic structures. The obtained electronic band structure for all Bi12MO20 compounds is semiconductor in nature. Similar to other oxides, there is a pronounced hybridization of electronic states between M-site cations and anions in Bi12MO20. Based on the obtained electronic structures, we further calculate the frequency-dependent dielectric function and other optical functions. [ABSTRACT FROM AUTHOR]

The effects of bend angle on the stability, electronic structure and optical properties of Li-absorbed borophene system are studied by using density functional theory based on the first principles. The structure of borophene did not change significantly after adsorption of a Li atom, and the planar structure of borophene was not destroyed. Bending deformation affects the stability of the adsorption system and reduces the binding energy of the adsorption system. The adsorption of Li atoms obviously changes the energy band structure of borophene, and more impurity levels appear in the conduction band. The 2s orbital of Li and the 3p orbital of B are obviously hybridised. A charge transfer occurs between Li atoms and borophene. As the deformation increases, the amount of charge transfer increases. The bending angle affects the size of the absorption peak and reflection peak of the adsorption system. [ABSTRACT FROM AUTHOR]

To study electronic structures and optical properties of 6H-SiC, the lattice parameter, band structure, density of state, electron density difference and optical property of 6H-SiC are investigated by applying the first-principles density functional theory based on the plane wave pseudo-potential method in this paper. The results show that 6H-SiC is an indirect band gap semiconductor, and the valence band top is located at Γ, the conduction band bottom is located at (0, 0·50, 0·06) of M-L. The valence-band top is primarily from the hybrid of 2p states of C and Si atoms, while the conduction band bottom is mainly from the hybrid of C 2s and Si 3p states. The electron density differences indicate that the bond type of Si and C in 6H-SiC are sp3 hybridisation. The calculation results for optical properties show that there is an obvious dielectric peak within the range of energy from 0 to 15 eV, with absorption band edge corresponding to ultraviolet band, therefore, the 6H-SiC material may be a type of excellent ultraviolet semiconductor materials. [ABSTRACT FROM AUTHOR]

In this paper, a CSVO3 phosphor for white LED has been successfully prepared by solid-state synthesis and has been characterized. The CsVO3 was simulated by Materials Studio software based on density functional theory (DFT). The results show that the CsVO3 sample has a direct optical transition with band gap energy of 3.143 eV. Under ultraviolet excitation in the range of 300–390 nm, the emission spectrum of CsVO3 phosphors ranges from 400 to 700 nm, and its peak emission spectrum is near 492 nm, and shows yellow color fluorescence emission. These results indicate that CsVO3 phosphor can be used as a promising white phosphor for white LED. [ABSTRACT FROM AUTHOR]

In this manuscript, the electronic structure, bonding nature and optical properties of the ternary Ba2HgS5 compound was investigated using the density functional theory (DFT). The generalised gradient approximation (GGA), Engel and Vosko generalised gradient approximation (EV-GGA) and the modified Becke Johnson (mBJ) schemes were used to model the exchange and correlation potentials. Band structure calculations indicate that this compound has a direct energy band gap value of 2.34 eV, showing a close agreement with the experimental band gap value of 2.40 eV. The energy band gap value calculated using the mBJ formalism is larger than those obtained from the GGA and the EV-GGA approaches. From the analysis of the partial electronic energy density of states, it was observed that the valence band is dominated by the Ba-p, S-s and Hg-d electronic states, while the conduction band is formed by the S-p and Ba-d orbitals. In addition, there exists a strong hybridisation in the valance band and in the conduction band between the S-p and Hg-s, Ba-s and Hg-f, Hg-s, S-p as well as the S-p and Hg-p states, respectively. This strong hybridisation leads to strong covalent bonding between the Hg-S and Ba-S atoms. Moreover, the optical constants were calculated and discussed in details. The energy dependent optical parameters were found to be anisotropic with respect to the polarisation of the incident electromagnetic wave and exhibit features in complete agreement with the electronic band structure calculations. The compound absorbs ultraviolet radiation quite strongly. Ba2HgS5 possesses high refractive index over a wide range of frequency and has potential to be used as anti-reflective coating and also in photonic devices like in light emitting diodes (LEDs). [ABSTRACT FROM AUTHOR]

Six new low-band-gap copolymers of donor--donor--acceptor (D-D-A) architecture have been designed using density functional theory and time-dependent density functional theory methods in order to use them in organic photovoltaic cell (OPVC). Phenanthro [3,4-d:9,10-d'] bis ([1,2,3] thiadiazole)-10,12-dicarbonitrile moiety has been used as an acceptor for all compounds. We insert benzo [1,2-b:4,5-b'] dithiophene and, N,N-diphenylbenzo [1,2-b:4,5-b'] dithiophen-2-amine units as donor to complete designing of copolymers. In order to tuning the optical and electronic properties, we have modified the donor unit by substituted with amine, methoxyamine, N-methylenethiophen-2-amine, methoxy, alkoxy moieties. The band gap (Eg), HOMO and LUMO values and plots, open circuit voltage (VOC) as well as optical properties have been analysed for designed copolymers. The optimised copolymers exhibit low-band-gap lying in the range of 1.03-2.24 eV. DPTD-6 copolymer presents the optimal properties to be used as an active layer due to its low Eg (1.03 eV) and a moderate VOC (0.56 eV). Thus, OPVC based on this copolymer in bulk-heterojunction composites with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as an acceptor has been modelled. Eg and VOC values of composite material DPTD-6:PCBM are found as 1.32 and 0.65 eV, respectively. A model band diagram has been established for OPVC, simulating the energy transfer between active layers. [ABSTRACT FROM AUTHOR]

Electronic structure and optical properties of the CdXO3and ZnXO3(X˭Ge, Sn) compounds have been investigated based on density functional theory. According to the predictive results, reveal that the CdXO3and ZnXO3would be candidates for a high performance lead free optical crystal, which will avoid the environmental toxicity problem of the lead-based materials. [ABSTRACT FROM PUBLISHER]

In this study, we investigate the electronic structure and optical properties of α-RDX crystal under pressure from 0 to 4 GPa using first-principles calculations based on the density functional theory. When pressure increases, the calculations figure out that the band gap linearly decreases, the peaks of the total density of states are lowered, the valence bandwidths broadened and the conduction bandwidths compressed. The results also show that the optical properties including dielectric function, absorption spectrum, refractive index, reflectivity and energy-loss function respond to compression, that is, the intensity of the maximal peak of absorption coefficient increases from 7.07 × 104to 7.98 × 104cm−1with corresponding photon energy from 5.10 to 5.15 eV, the static refractive index increases from 1.23 to 1.30, the intensity of the maximal peak of reflectivity function increases from 0.24 to 0.32 accompanied by its photon energy from 5.74 to 5.97 eV, and the plasma resonance energy and its intensity increases from 5.92 to 6.20 eV and 3.81 to 5.13, respectively. [ABSTRACT FROM PUBLISHER]

The electronic structures and optical properties of tin dioxide (SnO2) with different Al-doping concentrations ( x = 0, 0·0185 and 0·0417) are investigated using the first-principles calculation of plane wave ultra-soft pseudo-potential technology based on the density functional theory under the local-density approximation. The results show that the Fermi level of Al-doped SnO2 goes into the valence band, indicating that Al-doped SnO2 is a typical p-type semiconductor. Moreover, with the increase in Al-doping concentrations, the band gap of SnO2 is broadened and the blueshift of the absorption spectrum becomes significant, which are in good agreement with the experiment results. In addition, the low reflectivity (<15%) in the visible light range is obtained. [ABSTRACT FROM AUTHOR]

Using the density functional theory calculations, we studied the structural, electronic and optical properties of zincblende Zn1−xCdxS and ZnS1−ySeyalloys. Calculated structures and band gaps of these alloys are in good agreement with available experimental and other theoretical values. Present results show that the prominent peaks of the dielectric functions and absorption coefficients have a slight red shift and the amplitudes become larger with the increasing concentration of Cd and Se. Moreover, present findings predict that Zn1−xCdxS and ZnS1−ySeyalloys are promising for solar cells and photoconductor and electroluminescent devices due to their high absorption of solar radiations and photoconductivity in the energy region from visible light to ultraviolet. [ABSTRACT FROM PUBLISHER]