Aleksey S. Perepelitsa

Optical and structural properties of ensembles of colloidal Ag2S quantum dots in gelatin

The size dependences of the absorption and luminescence spectra of ensembles of hydrophilic colloidal Ag2S quantum dots produced by the sol-gel method and dispersed in gelatin are analyzed. By X-ray diffraction analysis and transmission electron microscopy, the formation of core/shell nanoparticles is detected. The characteristic feature of the nanoparticles is the formation of crystalline cores, 1.5–2.0 nm in dimensions, and shells of gelatin and its complexes with the components of synthesis. The observed slight size dependence of the position of infrared photoluminescence bands (in the range 1000–1400 nm) in the ensembles of hydrophilic colloidal Ag2S quantum dots is explained within the context of the model of the radiative recombination of electrons localized at structural and impurity defects with free holes.

Photoinduced Degradation of the Optical Properties of Colloidal Ag2S and CdS Quantum Dots Passivated by Thioglycolic Acid

The results of studying degradation of the optical properties of colloidal Ag2S and CdS quantum dots (QDs) 2.6–3.2 nm in size passivated by thioglycolic acid (TGA) are presented. The photoluminescence intensity of colloidal Ag2S QDs has been found to decrease under laser irradiation at a wavelength of 445 nm, beginning with the effective power of 10 mW. The observed effect is interpreted as a photochemical reaction of formation of new nonradiative-recombination channels in Ag2S QDs upon excitation. It is established for colloidal CdS QDs passivated by TGA that a decrease in the optical density in the entire absorption spectrum and the luminescence intensity is accompanied by precipitation of the colloidal particles in a cell and related to photodegradation of the passivating shell.

Nonlinear optical absorption of non-spherical silver nanoparticles and organic dyes mixtures

We study the features of the nonlinear optical response of silver nanoparticles (Ag NPs) of spherical and triangular shapes synthesized using a citrate-borohydride approach and their mixtures with methylene blue (MB). The Z-scans at the wavelengths of 532 nm using 10 ns pulses were used to analyze the nonlinear optical absorption of MB solutions, Ag NPs of different morphology, particularly, the concurrence of saturable and reverse saturable absorption in the solution of triangular Ag NP and MB. We show the significant contribution to the increasing in the normalized transmittance accomplished by photochemical degradation of the nonspherical Ag NPs (extinction maximum of 600 nm) and transformation into the spherical ones (extinction maximum of 400 nm). The nonlinear light scattering is also analyzed, which showed the contribution to the variation of the sample transmission when it approaches the focal plane. It is shown that the nonlinear optical response is not additive in the mixture of Ag NPs and MB. The increasing of the nonlinear absorption is probably due to both a change in the population of the triplet states of the dye and the efficiency of photochemical degradation of NPs in the presence of MB. At present, research in the field devoted to the development of control techniques for nonlinear optical properties of organo-inorganic nanostructures is relevant. The occurrence of interaction manifestations in other properties, in particular nonlinear optical, is of undoubted interest, including a practical one. For mixtures of plasmon nanoparticles (NPs) and dyes, studies of this kind are virtually unknown in the literature. In particular, the presence of plasmon NPs near MB can affect the probabilities of optical transitions and the mechanisms of photophysical processes in the molecule. However, the effect of plasmonic NPs on the two-photon absorption (TPA), the saturable absorption (SA), and the reverse saturable absorption (RSA) of MB has not been performed yet. In this paper, we report the studies of the nonlinear absorptive characteristics of mixtures of Ag NPs and MB in colloidal solutions using 10 ns pulses at the wavelength of 532 nm. The measurements of the nonlinear optical properties of our samples were carried out by the standard Z-scan technique. The Nd:YAG laser generated single pulses (λ = 1064 nm, τ=10 ns) at 1 Hz repetition rate. The probe second harmonic (λ=532 nm) of this radiation generated in KDP crystal was focused by a 300-mm focal length spherical lens. The laser pulse energy was measured by a first calibrated photodiode and then registered by a digital * Corresponding author: Ovchinnikov_O_V@rambler.ru

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.