Optical energy gap

The near-IR spectra of crystalline samples of the two radical dimers [22]2 (R1 =Me, Et R2 = H) were measured <2005JA18159>. The absorptions in the mid-IR region between 650 and 3100 cm-1 are due to molecular vibrations of the dimer. A well-developed, low-lying absorption cutoff was interpreted as corresponding to a valence band to conduction band excitation. The optical energy gap values are qualitatively in agreement with the values predicted by the LMTO band structure calculations. 

The existence and variation of optical energy gap may be also explained by invoking the occurrence of local cross linking within the amorphous phase of the matrix network, in such a way as to increase the degree of ordering in these parts. 

Having determined the optical energy gap AE, the family of the absorption curves in the region of the fundamental band edge presented in Fig. la provides the possibility of obtaining the relationship between AE pj and the electron density (Fig. 3). As in the case of indium antimonide, such a relationship for AEpp may be due to the smallness of the effective mass of electrons, according to Burstein [8]. 

Fig. 3. Variation in the optical energy gap AEopt (1) and the optical effective mass of the electrons mn/nio (2) with their density in the alloy 0.7 InSb-0.3 InAs a) mj from the free-carrier contribution to the dielectric constant b) mn from plasma resonance.

Devices based on a-SiC H have certain advantages over other semiconductor materials in a number of applications in optoelectronics, such as thin-film light-emitting diodes, coatings for laser facets, and a broadband window material for amorphous solar cells [163-165], These applications exploit the fact that the optical energy gap and the refractive index of the films can be varied by changing their chemical composition. 

In most covalent NCS it is found that AE, the thermal activation energy of the conductivity is about half the magnitude of the optical energy gap. This means that Ep is not far from the center of the mobility gap. Does this mean that these materials are intrinsic In the case of crystalline semiconductors the word intrinsic is used to mean that the conduction properties are not affected by the presence of localized impurity states. The position of Ep is then determined by the equality... 

Table 4.8 Molecular structure, oxidation and reduction peak potentials and maximum absorption of thienyl-S,S-dioxide-EDOT co-oligomers oxidation and reduction redox potentials, electrochemical energy gap, maximum absorption, optical energy gap and p-conductivity of the corresponding polymers obtained by anodic polymerization...

Madler et al. [127] carried out synthesis of stable ZnO nanocrystallites down to 1.5 nm in diameter by spray combustion of Zn/Si precursors. These crystallites exhibited a quantum size effect a blue shift of light absorption with decreasing crystallite size and the wet-phase-made ZnO QDs nicely followed a correlation between particle size and optical energy gap from the literature. 

FIGURE 10 Optical energy gap versus fluence for ion-implanted polysterene, polypropylene, and polyamide 6. (Adapted from Refs. 79 and 82.)... 

Thin film absorption spectra from pristine film spin-cast from 5 mg/mL TCE solution Optical energy gap estimated from the onset of the film absorption Cyclic voltammetry determined using Fc/Fc (Fhomo = -80 eV) as external reference... 

The diamagnetic compound is a semiconductor with an optical energy gap of about 2.2 eV [419. ... 

The refractive index, the absorption index and the absorption coeflScient of vacuum deposited films of PrO, prepared under varying conditions have been evaluated by Goswami and Goswami (1975) from the transmittance data as a function of wavelength in the visible region. The optical energy gap is estimated at 3.40 eV. 

Chouksey et al. [156] have investigated the EL of CdS nanoparti cl es-polyvinyl carbazole composites. They have prepared the thin films of CdS nanoparticle-polyvinyl carbazole (PVK) composite using chemical method. The absorption spectra and EL of the films doped with different concentrations of CdS nanoparticle have been measured. The absorption of pure PVK film starts at 290 nm wavelength in which a peak appears at 270 nm, indicating that the optical energy gap of PVK film is 4.26 eV. The absorption onset of CdS-PVK thin films is obtained at 300 nm, which... 

Both CdCr2S4 and CdCr2Se4 are ferromagnetic, and magnetic, electrical, and optical energy gap data for them are shown in Table 6. The octahedral crystal field quenches the orbital angular momenta... 

Fig. 19. Optical energy gap of CdCr2Se4 as a function of temperature (after Shepherd ).

Some Structural, Magnetic, and Optical Energy Gap Data for Eu Chalcogenides ... 

Fig. 20. Optical energy gap as a function of applied magnetic field at 20.1°K for EuS (after Busch and Wachter ).

If the relevant maxima and minima lie at the same k value as it is fulfilled in Fig. 2.9 we speak of a direct transition. In the case of an indirect transition, that is if these extreme values do not lie at the same value of k, as in the case of the s-bands (H chain) discussed, the parameter g in Eq. (2.33) merely represents the thermal energy gap . An optical energy transition is (without phonon support) only possible at constant k value. The optical energy gap is then accordingly greater. 

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