Yu. V. Malyukin

Low-temperature spectroscopy of nonequivalent Pr3+ optical centers in a Y2SiO5 crystal

An analysis of the absorption and luminescence spectra of a Y2SiO5:Pr3+ crystal has revealed the existence of two Pr3+ optical centers associated with the presence of impurity ions at nonequivalent cation sites. It is found that energy is transported nonradiatively between the nonequivalent Pr3+ optical centers. and a preliminary analysis of the transport mechanism is carried out.

Optical spectroscopy of disorder in molecular chains (J-aggregates)

The form of the exciton absorption band for 1D molecular chains and their luminescence are investigated in glass matrices of various composition and in Langmuir–Blodgett (LB) films under selective excitation. It is shown that the exciton absorption band for 1D chains is always asymmetric. The shape of the low-frequency edge of their absorption band changes from the Gaussian to the Lorentzian depending on the method of obtaining of 1D chains due to a change in the diagonal and off-diagonal disorder in molecular chains. Under selective excitation of 1D molecular chains, the effect of considerable luminescence band narrowing is not observed. This is associated with statistical properties of the exciton absorption band and with relaxation processes in the materials under investigation in the excited state.

Microscopic nature of Pr3+ optical centers in Y2SiO5, Lu2SiO5, and Gd2SiO5 crystals

The results of investigations of the energy spectrum, energy relaxation channels, and dynamics of electronic excitations of Pr3+ optical centers in Y2SiO5, Lu2SiO5, and Gd2SiO5 crystals are reviewed. It is shown that the crystal field of the ligands of nonequivalent cationic sites in these crystals preserves the quasisymmetry of distorted octahedra and tetrahedra; the Pr3+ activator ions are nonuniformly distributed over the nonequivalent cationic sites in Y2SiO5. For high concentrations of activator ions (>1at.%) in Y2SiO5 crystals, the luminescence is quenched as a result of the migration and trapping of the electronic excitations energy of optical centers by traps. For Y2SiO5: Pr3+ the low-temperature mechanism of dephasing of the optical transitions of Pr3+, which is not characteristic for crystals and is due to the interaction of impurity ions with two-level systems of a multiwall adiabatic potential, is analyzed.

Echo spectroscopy of two-level systems in a Y2SiO5: Pr3+ crystal

The results of an experimental investigation of low-temperature optical spectra and phase relaxation of electronic excitations of Pr3+ impurity ions in a Y2SiO5 crystal are reported. It is established that at low temperatures spectral lines are broadened by a mechanism that is uncharacteristic for crystals and is due to the interaction of impurity ions with two-level systems. The constants characterizing the interaction of Pr3+ impurity ions with phonons and two-level systems are found.

Time-resolved luminescent spectra of J-aggregates with exciton traps

The possibility of coexistence of free and self-trapped excitons in one-dimensional molecular chains (J-aggregates) has been proved on the basis of experimental study of time-resolved low-temperature luminescence spectra.

Accumulation of oxacarbocyanine dyes with different alkyl chain length in bone marrow cells and hepatocytes

A study was made of the inclusion of fluorescent probe H-510 based on 3,3′-dialkyloxacarbocyanine bromide (where alkyl is ethyl, nonyl, or octadecyl) into cells of different types. Alkyl chain length (C2, C9, or C18) was found to largely determine the accumulation dynamics and mechanism. Similar spectral characteristics for all probe types in bone marrow cells were found by microfluorimetry, suggesting insertion of dye molecules irrespective of their lipophilicity into micelle-like structures formed probably by cell phospholipids. Spectroscopy data indicate interaction of 3,3′-diethyloxacarbocyanine bromide (H-510/C2) and 3,3-dinonyloxacarbocyanine bromide (H-510/C9) dyes in hepatocytes with a less polar microenvironment (nonpolar and low-polar lipids that constitute a significant part of the total content of cell lipids). The fluoresccence maximum of long-chain dye H-510/C18 in hepatocytes is shifted to the short-wavelength region and strictly coincides with the fluorescence maximum of the probe in an albumin solution. It is not excluded that inclusion of the probe into cells occurs via endocytosis upon its binding to surface proteins.

Processes of energy migration in mixed europium–lanthanum magnesium borate nanocrystals

ABSTRACT Processes of excitation energy migration in europium magnesium borate nanocrystals at different concentrations of neodymium and lanthanum ions were investigated by steady-state and time-resolved luminescence spectroscopy. Energy migration in neodymium doped mixed europium–lanthanum magnesium borate nanocrystals is well fitted by ∼t0.33 dependence indicating one-dimensional transport to neodymium energy acceptors through europium chains. Variation of neodymium and lanthanum concentrations have shown that at room temperature excitation can migrate over the distances up to 100 nm that is comparable with the size of nanocrystal.

New channels of photon echo relaxation in Y2SiO5:Pr3+ and LaF3:Pr3+ crystals

Experimental results on the investigation of low-temperature optical absorption spectra and temperature dependence of the photon echo (PE) amplitude signal in Y2SiO5:Pr3+ and LaF3:Pr3+ crystals at the transition 3H4(0)−3P0 of the Pr3+ ion are presented. It is shown that additional relaxation channels exist for PE in addition to the known phonon mechanisms. This is associated in a LaF3:Pr3+ crystal with the temperature variation of dipole moment at the Pr3+ ion transition. In a Y2SiO5:Pr3+ crystal, this is due to the thermally activated transitions for the Pr3+ ion between nonequivalent positions in the crystal lattice.