Self-assembled quantum dots (QDs) in double-layer InAs/GaAs structures are studied by resonant photoluminescence and photoluminescence excitation spectroscopy. A weakly correlated (50%) double-layer system with an array of vertically coupled QDs (asymmetric quantum-dot molecules) was formed in a structure consisting of the 1.8-monolayer-thick first and the 2.4-monolayer-thick second InAs layers separated by 50 monolayers of GaAs. The nature of discrete quantum states in this system was studied and resonances corresponding to vertically coupled QDs were clearly observed for the first time.

A possible mechanism of photoinduced annealing of intrinsic defects in quantum dots with a hexagonal crystal structure is justified on the basis of the studies of the kinetics of photoinduced decay of luminescence of CdSxSe1−x quantum dots synthesized in a glass matrix and ab initio calculations of chemical bond energies at the interface in the n(CdSe)-SiOx-type cluster. The model proposed implies that photoinduced Se-O bond breaking at the anionic face results in an increase in electric field inside the quantum dot; this field stimulates cadmium vacancy diffusion to the surface. This model accounts for the degradation of luminescence and of the parameters of nonlinear optical devices observed during photoinduced annealing.

This work deals with effective passivation of CdSXSe1−X quantum dot surface after treating it by low-temperature hydrogen RF plasma. An enhancement of the exciton luminescence was observed, which can be interpreted as consequence of a decreasing number of surface non-radiative traps.

The low-temperature photoluminescence and Raman scattering in CdSe/ZnSe nanostructures with individual CdSe inserts of 1.5 and 3.0 monolayers in nominal thickness were studied. The energy position of the photoluminescene band is governed by interdiffusion of Cd and Zn into the insert regions, whereas the shape of this band is controlled by strong interaction of localized excitons with optical phonons in the Zn 1− x Cd x Se solid-solution insert. Multiphonon processes of excitonic relaxation with involvement of acoustic phonons at the Brillouin zone edges are also important. The results obtained are interpreted in the context of a model for the effective excitonic mobility edge.

A temperature dependence of the optical energy gap E g (T) for the CdSxSe1−x quantum dots synthesized in a borosilicate glass matrix was investigated in the range of 4.2–500 K. It was demonstrated that this dependence reproduced the dependence E g (T) for bulk crystals and is described by the Varshni formula for \(\bar r > a_B \) over the entire temperature range. Here, \(\bar r\) is the average dot radius, and aB is the Bohr radius for the exciton in a bulk crystal. With the transition to quantum dots with \(\bar r > a_B \), a decrease in the thermal coefficient of the band gap and a deviation from the Varshni dependence were observed in the temperature range of 4.2–100 K. The specific features observed are explainable by a decrease in the resulting macroscopic potential of the electron-phonon interaction and by modification of the vibration spectrum for dots as their volume decreases.

The structure of two types of GaAs i-n−-n-n+ epilayers on GaAs〈100〉 semi-insulating substrates was studied by electron microscopy. The low-temperature photoluminescence spectra were measured and their special features were analyzed. It is shown that the formation of dislocations during growth in such structures significantly affects the photoluminescence spectra and impairs the parameters of microwave field-effect transistors based on these structures.

Hyperbolic excitons have been detected in layered semiconductor BiI 3 . Their main parameters have been evaluated.

We report the results of a comprehensive study of lattice dynamics by means of far-infrared phonon spectroscopy in quaternary semimagnetic narrow-gap single crystals. A new version of the isodisplacement model is developed which takes into account the peculiarities of the dielectric function of narrow-gap semiconductors. This new approach is used to describe the phonon spectra transformation with composition for quaternary materials and is found to be in excellent agreement with the experimental data. The evidence for better quality and more stabilized crystalline structure of in comparison with ternary is presented and ascribed to the effect of magnetic doping.

We present new results on infrared photoluminescence and photoluminescence excitation spectroscopy in . We find that the phonon coupling significantly influences the optical spectra of this direct narrow-gap semiconductor. In a small spectral region close to the fundamental energy gap, indirect `hot exciton' absorption with participation of longitudinal optical phonons is the main absorption mechanism. A qualitative theoretical explanation is given. Furthermore, new experimental arguments for the excitonic nature of the optical transitions in the spectral region of the fundamental gap in this narrow-gap material are provided. We find that knowledge about the excitonic processes in wide-gap semiconductors can also be applied to high-quality narrow-gap materials.

In presented work the Raman spectra of the family of ferroelectric crystals A(3)B(2)C(9), ( here A=Cs, Rb; B= Sb, Bi; C= Br) are given and the assignment of some high frequency bands is fulfilled. The conclusion about possible difference of structure of the crystals Rb3Bi2Br9 and Rb3Sb2Br9 from well known and detaily investigated structure of Cs3Bi2Br9 crystal is made.We also suggest that significant variation of spectra in the temperature region 110 - 300K can be not only due to phase transition effects but also owing to anharmonic Fermi resonance between one- and two phonon excitations.

A comprehensive study of lattice dynamics for quaternary semimagnetic narrow-gap Hg1-x-yCdxMnyTe and Hg1-x-yCdxMnySe single crystals has been carried out by means of FIR phonon spectroscopy. All of the vibration states are identified and interpreted. The three-mode behavior of phonon spectra transformation with composition variation is proved. A new version of isodisplacement model is developed in order to include the peculiarities of dielectric function for narrow-gap semiconductors. This new approach is used for description of phonon spectra transformation under composition variation for quaternary material and shows an excellent agreement with the experimental data obtained. The strong evidence of more perfect and stabilized crystalline structure for Hg1-x-yCdxMnyTe(Se) in comparison with ternary Hg1-xCdxTe(Se) is presented and ascribed to the effect of magnetic doping, The optimal doping is found and interpreted in terms of exchange interaction of free carrier spins with localized magnetic moments of magnetic impurities. Novel features of lattice dynamics for mercury based compounds are found to be of common nature with those for superionic materials and interpreted in terms of double-well potential theory developed for the case.

Infrared (IR) and Raman spectra (RS) of β-alanine single crystal and polycrystalline samples have been measured in the 4000–10 cm−1 range. Factor-group analysis have been made and the number of normal vibration modes was calculated. The assignment of the observed vibrational frequencies to corresponding symmetry type and the molecular fragments have been performed.

It is shown that intense optical excitation of CdS x Se 1−x nanocrystals in a glass matrix in the region of interband transitions leads to their heating, which manifests itself in a reversible longwave shift of the near-edge dopant-defect photoluminescence band. Estimates of the temperature with account for the volume expansion of a nanocrystal and the adjacent glass matrix are presented.

In the present work the Raman spectra of the family of ferroelectric crystals A3B2C9 (where A = Cs, Rb; B = Sb, Bi; C = Br) are given and the assignment of some high-frequency bands is fulfilled. Conclusions about possible differences between the structure of Rb3Bi2Br9 and Rb3Sb2Br9 crystals from the well-known and detailed structure of Cs3Bi2Br9 crystals are made. We also suggest that the significant variation between the spectra in the temperature range 77–300 K can be not only due to phase transition effects but also to anharmonic Fermi resonance between one- and two-phonon excitations.

Raman spectra of some A 3 B 2 C 9 ferroelectric crystals (here A=Cs, Rb; B=Sb, Bi; C=Br) have been obtained, and a number of high-frequency bands have been assigned. The Rb 3 Bi 2 Br 9 and Rb 3 Sb 2 Br 9 crystals are shown to differ in structure from Cs 2 Bi 2 Br 9 . The qualitative changes in the spectra in the 77–300 K temperature interval can be associated not only with structural phase transitions, but with the effect of the anharmonic Fermi resonance between one-and two-phonon excitations as well.

On the basis of experimental investigations of authors the expediency of using photoluminescence (PL) method in gallium arsenide semiconductor device technology is shown.

The influence of high power resonance electromagnetic radiation on a Frenkel exciton system is studied. By means of the Keldysh diagram technique a formula for the nonlinear susceptibility is obtained. The influence of the excitation intensity on the shape of exciton band and on the value of the absorption coefficient is established. The phenomena of optical bistability and multistability are considered taking into account the nonlinear boundary conditions.

Energy levels structure of the CdSxSe1-x microcrystallites in the glass matrix has been obtained from the analysis of the absorption spectra taking into account the crystallite random orientation, the confinement effect and the dispersions of both microcrystallite radius and composition. The peculiarities of the absorption saturation have been determined.