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The (Mg,Zn)O Alloy
Published in Zhe Chuan Feng, Handbook of Zinc Oxide and Related Materials, 2012
Holger von Wenckstern, Rüdiger Schmidt-Grund, Carsten Bundesmann, Alexander Müller, Christof P. Dietrich, Marko Stölzel, Martin Lange, Marius Grundmann
In Figure 10.21a, the Urbach energy of MgxZn1−xO [146] is plotted for Mg-contents up to about 34%. The Urbach energy increases from about 30 meV for x = 0 to about 110 meV for x = 0.34. The increase of E0 is within the error bars of the experiment linear for the whole composition range and this is indicated by the solid line in Figure 10.21a following the functional dependence: E0(x) = (34.31 + 1.96 × x)meV. In Figure 10.21b, the Urbach energy of Mg0.05Zn0.95O:Ga [141] is plotted versus the Ga-content. Similar to Figure 10.21a, the Urbach energy increases linearly with increasing dopant concentration. The Urbach energy of nominally undoped Mg0.05Zn0.95O as read off from the linear fit in Figure 10.21a is roughly 42 meV. Introducing additionally 0.05% Ga increases the Urbach energy to about 100 meV for this alloy composition.
Optical Spectra in Perfect Crystals: Final State Interaction
Published in Yuzo Shinozuka, Electron-Lattice Interactions in Semiconductors, 2021
Then, if we apply the rule to the Urbach energy region in the optical absorption, we could obtain the emission spectrum as Iem(hv)∝exp(−hvkBT)Iab(hv)∝exp((σ−1)hvkBT). This form suggests the following conclusion: When σ < 1, the emission spectrum exhibits a decreasing function of hv; this is consistent with free exciton annihilation: F-type.When σ > 1, the emission spectrum exhibits an increasing function of hv; this is consistent with self-trapped exciton annihilation, showing a gaussian spectrum with a large Stokes shift: S-type. These statements are consistent with experimental and also theoretical results (Table 5.1).
Effect of UV radiation on the optical properties of PANI-Cu/PC and PANI-Cu/PC-PBT nanocomposites
Published in Radiation Effects and Defects in Solids, 2021
S. A. Nouh, M. ME. Barakat, Renu Gupta, K. Benthami, Radiyah A. Bahareth
Disordered materials possessed tail sates in the gap-region that present under the basic absorption edging. Further, it can be calculated applying the Urbach equation (26): where α is the absorption coefficient, αo is the material constant. Urbach energy is expressed by EU and refers to the tail width of the localized states in the bandgap; it represents the degree of disorder (27). The values of Eu were determined for the PANI-Cu/PC and PANI-Cu/PC-PBT NCPs by plotting the relation between lnα and photon energy. The values of EU of PANI-Cu/PC NCP samples increased from 0.70 to 0.74 eV with raising the UV fluence up to 120 J/cm2 due to crosslinking. While, it increased from 0.72 to 0.76 eV for the PANI-Cu/PC-PBT NCP samples; confirming the prevalence of crosslinking (Figure 3).
Optical, structural characterization and dielectric relaxation of [C2H5NH3]2ZnCl4 compound
Published in Phase Transitions, 2018
C. Ben Mohamed, K. Karoui, A. Ben Rhaiem
The Urbach energy Eu is a very important parameter to characterize the disorder of a material. It corresponds to transitions between extended states of the valence band and localized states of the conduction band, Bougrine et al. [30]. From the variation of the absorption coefficient it is possible to deduce the disorder in the compound. Thus, the absorption coefficient is associated to the disorder by the empirical relation-ship [31]:By plotting Lnα as a function of energy hυ (Figure 10), we can access the value of Eu:Where α0 is a constant and Eu is the Urbach energy. The width of the located states energy or Urbach energy Eu was estimated from the slopes of Ln(α) versus (hυ) plots (Figure 9). The value of Eu is 2.19 eV. The dependence of the optical absorption coefficient with photon energy may arise from electronic transitions between localized states.
pH reaction effect on biosynthesis of CuO/Cu2O nanoparticles by Moringa oleifera leaves extracts for antioxidant activities
Published in Inorganic and Nano-Metal Chemistry, 2023
Mohammed Larbi Ben Amor, Saad Zeghdi, Salah Eddine Laouini, Abderrhmane Bouafia, Souhaila Meneceur
The higher value of Urbach energy (Eu) shows lower crystallinity and disorder in the nanomaterials. Urbach energy is sometimes known as Urbach’s tail and can be detected by ultraviolet spectra. The Urbach energy is determined by taking the reciprocal values of the slopes of the linear part of the vs. photon energy (Figure 6d).[64] Sometimes, Urbach energy is necessary to find the crystallization rate of nanoparticles.[88] The estimated Urbach energy values for the samples are given in Table 1.