Vibronic spectra of chlorophyll and its analogs. Influence of isocyclic substitution

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 55, No. 1, pp. 58–63, July, 1991.     

Effect of binding energy on the kinetics of radiative and nonradiative recombination of bound excitons

Radiative and nonradiative lifetimes of bound excitons in GaSe with various binding energies are measured by the magnetooptical method using time-resolution spectroscopy. It is shown that both the radiative and nonradiative lifetimes of an exciton bound at an ionized center increase with the binding energy of an exciton with a defect. Possible reasons for this dependence are considered. The results of calculations obtained in the framework of the proposed model are in good agreement with experimental data.     

Application of the Monte Carlo method for modeling passage of ultrashort laser pulses through an inhomogeneous medium with moving scatterers

We present the results of numerical modeling of passage of ultrashort laser pulses through an inhomogeneous layered medium with moving scatterers, based on solution of the nonsteady-state radiation transport equation by the Monte Carlo method. We consider the effects of Doppler broadening of the backscattered radiation spectrum in biological tissues. We have analyzed the dynamics of propagation of a short laser pulse within a multilayer model of human skin. We have studied the possibilities for tomography of different layers of biological tissue based on analysis of the spectrum of the scattered radiation pulse.     

Enhanced Raman scattering provided by fullerene nanoclusters

Two new nonlinear optic effects are observed in crystalline solutions of fullerenes in toluene and carbon tetrachloride. Both are provided by a self-clustering of the solute molecules and are referred to fullerene-enhanced Raman scattering and solvent-enhanced luminescence. The effects are induced by the excitation of charge-transfer states of the fullerene nanoclusters, which makes the latter act as amplifiers of local electric fields. The text was submitted by the authors in English.     

Influence of the structure of fullerene molecules on their clusterization in the crystalline matrix

The influence of the processes occurring during clusterization of fullerene molecules in solutions on their nonlinear optical properties has been considered. A new derivative of fullerene C₆₀, namely, monofulleropyrrolidine containing a specific group, which is known as sterically hindered phenol, has been analyzed using the previously proposed criteria, i.e., an empirical criterion, which is involved in the analysis of the emission spectrum of the frozen solution, and a theoretical criterion, which is based on the quantumchemical calculation. The performed experimental investigations of the frozen solution of this fullerene derivative in toluene completely confirmed the conclusions following from the results of theoretical calculations and demonstrated a low efficiency of the clusterization of fullerene molecules in this solution and, correspondingly, a low efficiency of its nonlinear optical response. It has been shown that quantum-chemical calculations can serve as the basis for prior testing of possible fullerene derivatives for the subsequent controllable chemical synthesis of a derivative with required properties.     

Spectroscopy of resonant excitation of exciton luminescence of GaSe–GaTe solid solutions

The luminescence excitation spectra of localized excitons in GaSe_0.85Te_0.15 solid solutions have been investigated at the temperature T = 2 K. It has been shown that the excitation spectra of excitons with the localization energy ε > 10 mV exhibit an additional maximum M _E located on the low-energy side of the maximum corresponding to the free exciton absorption band with n = 1. It has been found that the shift in the position of the maximum M _E in the excitation spectrum with respect to the energy of detected photons increases as the energy of detected photons decreases, i.e., with an increase in the localization energy of excitons. Under the resonant excitation of localized excitons by a monochromatic light from the region of the exciton emission band, in the exciton luminescence spectrum on the low-energy side from the excitation line, there is also a maximum of the luminescence (M _L ). The energy distance between the position of the excitation line and the position of the maximum in the luminescence spectrum increases with a decrease in the frequency of the excitation light. The possible mechanisms of the formation of the described structure of the luminescence excitation and exciton luminescence spectra of GaSe_0.85Te_0.15 have been considered. It has been concluded that the maximum M _E in the excitation spectrum and the maximum M _L in the luminescence spectrum are attributed to electronic–vibrational transitions with the creation and annihilation of localized excitons, respectively.