Intraband optical transition

The electronic structure is similar within each group as far as optical properties are concerned. For example, at the photon energy used in our experiments the optical response of the noble metals is entirely due to intraband optical transitions [22, while that of Ti, Zr, and Hf is dominated by interband transitions [23,24], The optical structures of Ni and Pd are more complicated, and both interband and intraband transitions can contribute [24,25. This interpretation is supported by the observation that the signals of largest and smallest magnitude occur in Zr and Ag, respectively. 

V.L. Rupasov, V.I. Klimov, Carrier multiplication in semiconductor nanocrystals via intraband optical transitions involving virtual biexdton states, Phys. Rev. B 76 (2007) 125321. 

Assuming that we have a metal in which the dominant contribution to the dielectric constant comes from intraband optical transitions e(o)) becomes... 

Our estimation shows that the radiative and nonradiative intraband transition rates may be comparable at certain temperatures, while at high or low temperature one of these mechanisms dominates. In particular, at room temperature nonradiative transitions are significantly faster. On the contraiy, at helium temperatures the radiative emission (with the energies to be order of 1 eV) corresponding to the intraband transitions can be observed. We suppose that the fast emission band with energies less than the exciton band observed at low temperatures [7] corresponds to the intraband optical transitions. 

Lasing on Intraband Optical Transitions in Semiconductor Nanocrystals... 

As an example, we estimate the resonance enhancement of an intraband optical transition in silicon carbide (SiC) nanociystals. The dielectric function of SiC is well modeled by the expressions (7) with = 6.52, Qt = 793.9 cm" (and the wavelength At = 12.6 pm), = 970.1 cm (Al = 10.3 pm), and y = 4.763 cm. Note that the relaxation parameter y is much less than the optical phonon frequencies, y/Qi = 0.006 and y/ L = 0.005. The solution of the resonance condition (6) results in Q w 902cm and the corresponding resonance wavelength A 11 pm. Here and hereafter, in all onr numerical estimates we accept the permittivity of a host matrix Shost = 2.25, because this value is typical for many solvents, glasses, and polymers. Then, the gain factor G(Q) is estimated to be approximately 3.6 x 10. ... 

Figure 10.3 Intraband optical transition of an electron at the bottom of the conduction band shown in E-k space.

Figure 1. Electron-hole coherent state is schematically illustrated for interband (a) and intraband (b) optical transitions.

Carrier relaxation due to both optical and nonradiative intraband transitions in silicon quantum dots (QDs) in SiOa matrix is considered. Interaction of confined holes with optical phonons is studied. The Huang-Rhys factor governing intraband multiphonon transitions induced by this interaction is calculated. The new mechanism of nonradiative relaxation based on the interaction with local vibrations in polar glass is studied for electrons confined in Si QDs. 

AETAIR Center develops long-wave infrared (EWIR) and terahertz-frequeney (THz) lasers operating at room temperature employing intraband lumineseenee in eolloidal semieonduetor nanocrystals, in which the optical transition frequencies can be easily tuned to the desired values by an appropriate choice of the semiconductor material and radius of the nanocrystals. 

Fast nonradiative relaxation of intraband transitions in semiconductor nanoeiystals with the relaxation times shorter than 1 picosecond is obviously the major obstacle of lasing on these optical transitions. Although, at present time mechanism of the nonradiative relaxation is not clear, it has been recently demonstrated experimentally that fast nonradiative relaxation of intraband transitions is mainly determined by their strong... 

In ordinary optical absorption there are two components associated with intraband transitions (Drude component) and interband transitions, respectively. A similar situation is encountered in magneto-optical spectroscopy. Of special interest is the interband component which is related to the joint density of states. The intensity of the magneto-optical transitions is proportional to the product of spin-orbit coupling strength and net electron-spin polarization of states excited by the incident light (Erskine and Stern, 1973). 

Figure 5.3. Illustration of optical transitions. Left interband transitions in a semiconductor, between valence and conduction states 1 is a direct transition at the minimal direct gap, 2 is another direct transition at a larger energy, and 3 is an indirect transition across the minimal gap Cgap. Right intraband transitions in a metal across the Fermi level ep...

Reports on several selected systems have produced various dynamical models for ultrafast excitations in nanoparticles [62, 107, 112, 113]. Many have used a widely accepted model to account for both the excitation and decay processes in metals. This involves the optical excitation of the electrons by interband and intraband transitions. These transitions are followed by a loss of coherence,... 

To describe the optical properties of the crystals over a wide temperature range and to derive the basic phenomenological parameters of the electronic transition, we fitted the R(co) and a(co) spectra using the Drude-Lorentz model. The Drude part describes the intraband transition of free carriers,... 

As already stated for other experimental parameters, two factors may account for the nonlinear optical response dependence on excitation wavelength Local field factor, f, and intrinsic nonlinear properties of the particles, x2 - The interband contribution to x2 expected to vary only for photon energies at least equal to the IB transition threshold, provided the intraband contribution remains negligible. On the other hand, the hot electron contribution, which accounts for the Fermi smearing mechanism, presents spectral variations for photon energies close to the IB transition threshold, since the electron distribution is modified around the Fermi level by the temperature increase subsequent to light absorption (see 3.2.3). The wavelength dependence of x has been already discussed in Section 6. 

Most of the descriptions of the magneto-optical results that will be presented in the following sections are of a qualitative nature and rely in one way or the other on the two microscopic models (interband or intraband transitions) sketched above. It is still open to discussion which of these two models is to be preferred. 

Fig. 7 (a) Schematic of the allowed ISe-lPe intraband transition, (b) Intraband and optical spectra of CdSe and CdS QDs respectively, (c) Even though both materials have very dissimilar band gaps, the relationships of the intraband energies with particle size are identical for both and is theoretically expected to follow the 1/r behavior (solid line). 

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