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Progress and Challenges of Semiconducting Materials for Solar Photocatalysis
Published in Inamuddin, Mohd Imran Ahamed, Rajender Boddula, Tariq Altalhi, Optical Properties and Applications of Semiconductors, 2023
Mridula Guin, Tanaya Kundu, Vinay K. Verma, Nakshatra Bahadur Singh
The number of charge carriers that are created by light absorption is dependent on the value of quantum yield (η). For the intrinsic semiconductors, the quantum yield remains almost constant with value close to η = 1. This is the case which is verified up to certain low-frequency range at which photogeneration starts, up to certain low-frequency range. Thus, one electron-hole pair is generated by the absorption of one photon. The remaining energy is used for the creation of phonons. On the other hand, at higher energy of irradiated light more than one pair of charge carriers are generated by the absorption of one photon, and thus, η > 1. Excess energy in this case is utilized for valence bond interband-impact ionization and generation of extra electron-hole pairs. Temperature can also impact the quantum yield value. With increase of temperature the band gap decreases. Therefore, the interband ionization moves towards lower value of light energy.
Fundamentals of Solar Radiation
Published in D. Yogi Goswami, Principles of Solar Engineering, 2023
Photovoltaic detectors normally use silicon solar cells to measure the short circuit current. Such detectors have the advantage of being simple in construction. Because heat transfer is not a consideration, they do not require clear domes or other convection suppressing devices. They are also insensitive to tilt as the output is not affected by natural convection. One of the principal problems with photovoltaic detectors is their spectral selectivity. Radiation with wavelengths greater than the band gap of the photovoltaic detector cannot be measured. Silicon has a band gap of 1.07 eV corresponding to a wavelength of 1.1 μm. A significant portion of the infrared part of solar radiation has wavelengths greater than 1.1 μm. Therefore, photovoltaic detectors are insensitive to changes in the infrared part of solar radiation.
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.
Preparation of different crystal types TiO2 materials and its photodegradation performance in Congo Red wastewater
Published in Phase Transitions, 2022
Jinwang Tian, Biyang Tuo, Jianli Wang, Yun Tang, Guanghua Nie, Yong Yang
The most common method for preparing TiO2 photodegradable materials was the sol-gel method. Compared with other methods, the sol-gel method has the advantages of simple process, mild reaction conditions and high product purity. Tripathi et al. prepared pure and mixed phase TiO2 by sol-gel method. The influence of calcination temperature on crystallite size, morphology, band gap and luminescence properties of resultant material have been investigated. The results show that the prepared samples having crystallite size between 19 nm to 68 nm were observed at different calcination temperatures. The energy band gap of materials decreases with increasing temperature. The PL intensity decreases as temperature increases but PL intensity starts increasing at higher temperature which shows the presence of mixed phase of anatase-rutile [29]. Therefore, the crystal structure of TiO2 has a huge influence on its photodegradation performance. It is necessary to study the relationship between TiO2 crystal structure and photocatalytic performance.
Systematic study of phase transformation, wide-to-narrow electronic band transition and optical properties of barium zirconium Oxynitrate: Ab initio calculations
Published in Molecular Physics, 2022
S. S. A. Gillani, Musaddaq Mukhtar, I. Zeba, M. Shakil, Tousif Hussain, Riaz Ahmad
Identical impacts have been reported in the literature that are accountable for band gap contraction [42–45]. At oxygen sites in BZO, the effect of nitrogen atom doping is examined, and the band structure is plotted in Figure 2. In all cases of doping the nature of band gap changes than that of pure BZO, i.e. both the maxima and minima of the VB and CB are respectively positioned at same k-points, indicating the direct nature as the VB maxima is at the G symmetry point instead of the R symmetry point. The band gap energy reduces upon doping. The wide energy gap decreases from 3.119 to 1.152 eV by N doping. Nitrogen belongs to the p-block elements in the periodic table and have properties of the V group of negatively charged elements with a slight difference in properties relative to oxygen. As the radius increases, the outermost shell goes far away from the nucleus and the electrons can be smoothly escaped; therefore, the electropositive propensity of the materials increases down the group. Thus, when going down the group, the band gap reduces.
A combined experimental and TDDFT-DFT investigation of structural and optical properties of novel pyrazole-1, 2, 3-triazole hybrids as optoelectronic devices
Published in Phase Transitions, 2021
I. H. El Azab, A. Ibrahim, M. Abdel El-Moneim, M. Sh. Zoromba, M. H. Abdel-Aziz, M. Bassyouni, A. F. Al-Hossainy
The theory of energy bands is an interesting way of visualizing differences between conductors, insulators, and semiconductors. The bandgap is the energy disparity between the valence bands and the substance conduction bands. Usually, the optical band gap can be calculated from the analysis of the spectral dependence of the absorption near the fundamental absorption edge. The absorption coefficient is well described by the following relation [63]: where is the energy of the incident photons and the factor B is a constant depends on the transition probability among the optical frequency range, and an energy independent constant having values between and (cm. eV)−1 [64,65].