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4 Host Lattice
Published in Vikas Dubey, Sudipta Som, Vijay Kumar, Luminescent Materials in Display and Biomedical Applications, 2020
Ramachandra Naik, S.C. Prashantha, H. Nagabhushana, Yashwanth V. Naik, K.M. Girish, H.B. Premkumar, D.M. Jnaneshwara
The bandgap of doped samples are as follows: Eu3+ doped samples exhibits in the range 5.63–5.87 eV, 4.9–5 eV for Tb3+ doped samples, 4.7–5 eV for Sm3+ doped samples, and 4.9–5 eV for Dy3+ doped samples. It was observed that, upon changing Ln3+ ions the bandgap changes because the charge carrier concentration increases. As the doping concentration increased, the density of states also improved and created a continuum of states resulting in the decrease of the bandgap (Naik et al. 2014a). This suggests decrease in the bandgap due to the inclusion of Ln3+ ions into Mg2SiO4 matrix which changes the electronic structure leading to the form of intermediate energy levels. Thus, Mg2SiO4:Ln3+ could be considered as ultraviolet absorption material, in which by varying the Fe content absorption energy can be adjusted.
Review of Solid State Physics
Published in Douglas S. McGregor, J. Kenneth Shultis, Radiation Detection, 2020
Douglas S. McGregor, J. Kenneth Shultis
Solid state materials used for radiation detectors are generally composed of crystalline materials. A crystalline material is defined by a basis of atoms arranged upon a periodic lattice. There are 14 possible Bravais lattice systems. The periodic arrangement of atoms causes the appearance of periodic potentials. This potential periodicity causes bands of allowed states to form, producing quasi-continua of energy states in these bands. The density of allowed energy states in these bands is defined by the density of states function. Gaps between these bands are referred to as energy gaps. The energy band that plays the part of atomic bonding is the valence band, and the energy band that plays the part in electron conduction is the conduction band. The energy gap between the valence band and the conduction band is referred to as the band gap.
Fundamentals of Nanoscale Electronic Devices
Published in Khurshed Ahmad Shah, Farooq Ahmad Khanday, Nanoscale Electronic Devices and Their Applications, 2020
Khurshed Ahmad Shah, Farooq Ahmad Khanday
The density of states is defined as the number of different states at a particular energy level that electrons are allowed to occupy. It is a measure of how closely the energy levels are to each other. It is defined as the number of available electron states per unit volume (dN) at energy “E” in the energy interval E and E + dE; then the DOS is given by g(E)=dN(E)dE
Theoretical investigation of the crystallographic structure, anisotropic elastic response, and electronic properties of the major borides in Ni-based superalloys
Published in Philosophical Magazine, 2020
Fangfang Xia, Michael D. Sangid, Yao Xiao, Xiaoguo Gong, Tieqiang Gang, Lijie Chen, Wei-Wei Xu
The elastic behaviour of these borides is further examined by means of exploring the bonding structure in these crystals. The total density of states (TDOS) and partial density of states (PDOS) are calculated, as shown in Figure 6. The total density of states (DOS) of a system reflects energy band structure. It describes the number of states per unit volume in a given interval of energy. A higher DOS value means more available number of states for electrons to occupy [46]. At the Fermi level, the total DOS value estimates the relative bonding electron numbers [47]. And the partial DOS represents the electronic occupation for the individual element in the unit cell. It can be seen in Figure 6 that the TDOS of MxBy are all across the Fermi level, implying these borides exhibit a metallic character. Additionally, in the TDOS of MxBy, some sharp peaks can be found in the valence bands and conduction bands, and they can be divided into two parts. The peaks in the conduction band are primarily determined by the M-d and B-p orbitals. In a relatively high valence band, the peaks originate from the contribution of the M-d and B-p orbitals. And then in a much lower valence band, the peaks become dominated by the B-s orbitals and M-d orbitals. According to the above discussions, near the Fermi level, the TDOS of MxBy mainly originate from the contribution of the M-d and B-p orbitals, indicating the transition metal atoms and B in terms of p-d hybridisation. Such strong hybridisation between the B-p and M-d orbitals form bonds with mixed metallic and covalent bonds, thus resulting in these borides exhibiting the high values of hardness.
Hydrogen Solution in Tetrahedral Interstitial Sites in ZrCo Hydrides: A First-Principles Study
Published in Fusion Science and Technology, 2023
The density of states reflects the possible number of states of electrons within the unit energy interval, which is of great significance for analyzing the bonding between atoms and material properties in materials.28 The electronic structures of Zr16Co16H(48+8f2), Zr16Co16H(48+4c1), Zr16Co16H48(8f1), Zr16Co16H(48+4c2), Zr16Co16H(48+8e), and Zr16Co16H(48+8g1) were calculated to further understand the physical characteristics of H occupying the sites in Zr16Co16H48. Figure 3 shows the partial density of states (PDOS) diagrams for Zr16Co16H(48+8f2), Zr16Co16H(48+4c1), Zr16Co16H48(8f1), Zr16Co16H48(4c2), Zr16Co16H(48+8e), and Zr16Co16H(48+8g1) under the 0 and 10 GPa. The Fermi energy level Ef position is regarded as zero energy. When the pressure is P = 0 GPa, taking Zr16Co16H48(8f1/4c2) as an example (Fig. 3e), it can be found that the H-s, Zr-d, and Co-d states are very similar in the energy range of −7.5 to −3.1 eV, which means that there is an obvious hybridization phenomenon in the H(8f1/4c2)-s and Co-d states, indicating that there is hybridization in the electron orbital. Although the H(8f1/4c2) and Zr atoms also have hybrid peaks, it was found that the peak similarity of H(8f1/4c2)-s and Co-d states was much higher than that of the H(8f1/4c2)-s and Zr-d states, and there were more hybrid peaks in the PDOS of the H(8f1/4c2)-s and Co-d atoms.
A simplified Bixon–Jortner–Plotnikov method for fast calculation of radiationless transfer rates in symmetric molecules
Published in Molecular Physics, 2023
A. I. Martynov, A. S. Belov, V. K. Nevolin
No experimental methods exist for measuring the density of states directly, but one can register absorption and emission spectra. According to the formula (25), intensity of fluorescence depends on the density of states multiplied by the transition frequency cubed. If one considers only a small energy range near , the intensity can be seen as dependent only on . As a result, the calculated function can be compared with the experimental data by Stockburger et al. [42] on the fluorescence spectra of naphthalene in gas phase at various excitation energies. In all registered spectra two peaks are present which stand out from the rest: the first one at 315 nm and the second one at 330 nm. The energy difference between them is ca. 1450 cm. Their position and shape do not change from one spectrum to another, but the peaks are denoted as different transitions on different plots. The authors attributed these peaks to B modes (506 and 938 cm) and an A mode (716 cm) in most cases. The identification of the peaks was approximate and based on the statement of Craig [41] who drew his conclusion from the characteristics of rotational splitting of the spectral lines. In our research, rotation was separated from the vibrational motion and was not considered. Instead, we suppose that the peaks taken by Stockburger originate from the A modes, one of which has a frequency of 1450 cm according to our calculation.