T. S. Kondratenko

Sensitization of photoprocesses in colloidal Ag2S quantum dots by dye molecules

Abstract. The effect of photosensitization of IR luminescence excitation (1205 nm) of colloidal Ag2S quantum dots (QDs) with average size of 2.5±0.6  nm in gelatin at 600 to 660 nm by molecules of 3,3’-di-(γ-sulfopropyl)-4,4’,5,5’-dibenzo-9-ethylthiacarbocyanine betaine pyridinium salt (Dye1) and thionine dye (Dye2) was registered. Cis-J-aggregates of Dye1 and cations monomer of Dye2 conjugated with Ag2S QDs take part in this process. The photosensitization of luminescence excitation of colloidal Ag2S QDs was interpreted by resonance nonradiation transfer of electronic excitation energy from cis-J-aggregates of Dye1 and cations of Dye2 to centers of recombination luminescence of Ag2S QDs.

Organic–inorganic nanostructures for luminescent indication in the near-infrared range

Amplifying and quenching of IR luminescence of colloidal Ag2S quantum dots were revealed to take place when they couple to organic dye molecules of 3,3′-di-(γ-sulfopropyl)-9-ethyl-4,5,4′,5′-dibenzothiacarbocyanine betaine and erytrosine pyridinium salts, respectively. The observed effects are explained as due to the formation of organic–inorganic heterostructures with different mutual arrangement of electronic states of the dyes and the quantum dots.

Absorption of light by colloidal semiconductor quantum dots

Abstract. UV-Vis absorption of colloidal cadmium sulfide quantum dots (QDs) synthesized by an aqueous synthesis in a gelatin matrix was investigated. Using the dipole approximation, taking into account the Coulomb interaction between the electron and hole in a QD and the polarization effects on the spherical boundary of QD and matrix, it was found the change of selection rules for optical transitions. It is shown that the optical absorption edge of QDs is formed by two optical transitions of electron between low-excited levels of size quantization of heavy hole (1S3/2 and 2S3/2), located in QDs valence band and fundamental size-quantized states 1Se of conduction band. These transitions are identical in intensity. Estimations of average values of CdS QDs radius were realized using the developed formalism for UV-Vis absorption spectra. These data were compared with experimental values of this parameter, obtained using transmission electron microscope.

The formation and luminescent properties of hybrid associates of colloidal Ag2S quantum dots with J-aggregates of trimethinecyanine dye

Spectral patterns of hybrid association in the mixture of colloidal Ag2S quantum dots (QDs) with an average size of 2.5 to 0.3 nm with J-aggregates of a pyridinium salt of 3,3’-di(γ-sulphopropyl)-9-ethyl-4,5,4’,5-dibenzothiacarbocyanine betaine (Dye), prepared by the sol-gel method in gelatin, are investigated. A conclusion about the preferential formation of cis-J-aggregates in the hybrid associates of Dye with Ag2S QDs is made. The effect of photosensitization of IR luminescence (1000–1300 nm) of colloidal Ag2S QDs by J-aggregates of Dye is revealed. On the basis of the results, a photosensitization scheme implying the resonance nonradiative transfer of the electronic excitation energy from cis-J-aggregates to the recombination luminescence centers of Ag2S QDs is suggested.

Decay of electronic excitations in colloidal thioglycolic acid (TGA)-capped CdS/ZnS quantum dots

Investigations of dynamics of exciton relaxation in colloidal thioglycolic acid (TGA)-capped CdS/ZnS core/shell systems with diameter of 3.6 nm by means of femtosecond transient absorption spectroscopy, thermostimulated luminescence (TSL), and decay of luminescence are presented in this paper. It was found that the intensity of trap-state luminescence increases when one and two ZnS monolayers are formed. Also, the lifetime of trap-state luminescence increases. Two types of trap states with different depths were found, using thermostimulated luminescence technique. Localized states of the first type with depth of 0.085 eV do not change their concentration during sell formation. In contrast, trap state of the second type with depth of 0.125 eV are almost completely removed. It was found that the electron lifetime, investigated femtosecond transient absorption is not changed during formation of ZnS shell. It was concluded that localized states are channels of non-radiative recombination, direct quenching the center of trap-state luminescence. The absence of exciton luminescence is caused by rapid localization of holes at luminescence center.

Luminescence and Nonlinear Optical Properties of Hybrid Associates of Ag2S Quantum Dots with Molecules of Thiazine Dyes

Spectral, kinetic, and nonlinear optical regularities that demonstrate the exchange of electronic excitations between the components of hybrid associates of Ag2S colloid quantum dots (1.7–1.8 nm) in gelatin with molecules of thiazine dyes (Ds) are found. When the IR luminescence of Ag2S quantum dots (QDs) is excited by radiation from the thionine absorption region, its enhancement due to nonradiative resonant energy transfer is observed. The association with methylene-blue molecules blocked the IR luminescence of Ag2S QDs upon its excitation by radiation from the absorption region of the dye due to the transfer of charge carriers. It is demonstrated that the hybrid association of thionine molecules and Ag2S QDs adversely affects the nonlinear optical properties of the latter, which manifests itself in inverse saturated absorption by the action of 10-ns second-harmonic pulses (532 nm) of a Nd3+:YAG laser. For the associates of Ag2S QDs with methylene-blue molecules, the radiation focusing caused by the transfer of charge carriers from the dye and the change in the population of small traps in nanocrystals is found. It is concluded that the direction of the transfer of electronic excitations and the photophysical processes in these objects are determined by the mutual arrangement of the HOMO–LUMO levels of the dye with respect to the levels of dimensional quantization of the Ag2S QDs.

Förster resonance energy transfer in hybrid associates of colloidal Ag 2 S quantum dots with thionine molecules

Nonradiative resonance energy transfer in hydrophilic hybrid associates of thionine molecules (TH+) with colloidal Ag2S quantum dots (QDs) with average diameter of 3.5 nm was studied. Photoluminescence spectra and its decay shown that for these systems the supplemental photosensitization of recombination luminescence of Ag2S QDs (1200 nm) from the region of TH+ fluorescence (618 nm) is possible. It was found that the average lifetime of TH+ molecules luminescence is shortened during their association with Ag2S QDs. Approximation of luminescence decay by stretched exponent with value of parameter β = 0.5 indicates on the inductive-resonance dipole-dipole (Förster) mechanism of nonradiative energy transfer (FRET). The efficiency of FRET was 0.29–0.41.