Alexey V. Povolotskiy

Photoluminescence properties of Eu3+ ions in yttrium oxide nanoparticles: defect vs. normal sites

The position of activator ions in the lattice has a fundamental effect on the luminescent properties of phosphors. In this paper, we describe the normal and defect sites of Eu3+ ions in a Y2O3 crystal lattice, their interaction and difference in physical properties. Analytically detectable amounts of defect sites reached in Y2O3:Eu3+ nanopowders with an average size of 40–50 nm were synthesized by a novel combined Pechini-foaming method. The luminescence properties of Eu3+ ions in defect sites are most pronounced in highly doped nanocrystalline powders (32 and 40 at%). To explain this phenomenon we suggest the mechanism of irreversible energy transfer from normal to defect sites of Eu3+ ions.

Up-conversion luminescence efficiency in Er-doped chalcogenide glasses

Abstract The efficiency of up-conversion luminescence of Er 3+ ions (excited by laser light operating at 810 nm) in the GeS 2 –Ga 2 S 3 :Er 2 S 3 system strongly depends on the energy position of the fundamental absorption edge. This dependence is due to non-radiative energy exchange between the electronic subsystem of the glassy matrix and excited levels of Er 3+ ions. In chalcogenide glasses Ge and Ga atoms are fourfold coordinated. Except for the M (M=Ge, Ga)–S heterobonds, the rest are M–M homobonds. These homobonds can be detected with Raman spectroscopy. The energy position of the absorption tail of the fundamental band depends on the concentration of M–M homobonds. When the concentration of these bonds increases the absorption edge shifts to longer wavelengths and the intensity of up-conversion luminescence decreases. The relative concentration of M–M bonds depends not only on composition of the glassy matrix but also on the synthesis and on concentration of extrinsic impurities such as OH − , SH − and –CH 2 –. Another cause of reduction of up-conversion luminescence intensity is the inhomogeneous distribution of REI in the Ga 2 S 3 –GeS 2 glasses. The simple model describing dependence of luminescence intensity on type of REI distribution in the glassy matrix is discussed.

Laser-induced transformation of supramolecular complexes: approach to controlled formation of hybrid multi-yolk-shell Au-Ag@a-C:H nanostructures.

In the present work an efficient approach of the controlled formation of hybrid Au–Ag–C nanostructures based on laser-induced transformation of organometallic supramolecular cluster compound is suggested. Herein the one-step process of the laser-induced synthesis of hybrid multi-yolk-shell Au-Ag@a-C:H nanoparticles which are bimetallic gold-silver subnanoclusters dispersed in nanospheres of amorphous hydrogenated a-C:H carbon is reported in details. It has been demonstrated that variation of the experimental parameters such as type of the organometallic precursor, solvent, deposition geometry and duration of laser irradiation allows directed control of nanoparticles’ dimension and morphology. The mechanism of Au-Ag@a-C:H nanoparticles formation is suggested: the photo-excitation of the precursor molecule through metal-to-ligand charge transfer followed by rupture of metallophilic bonds, transformation of the cluster core including red-ox intramolecular reaction and aggregation of heterometallic species that results in the hybrid metal/carbon nanoparticles with multi-yolk-shell architecture formation. It has been found that the nanoparticles obtained can be efficiently used for the Surface-Enhanced Raman Spectroscopy label-free detection of human serum albumin in low concentration solution.

Laser-induced synthesis of metallic silver-gold nanoparticles encapsulated in carbon nanospheres for surface-enhanced Raman spectroscopy and toxins detection

Metallic silver-gold nanoparticles (1–5 nm) encapsulated into carbon nanospheres (20–30 nm) were synthesized via laser-induced chemical liquid phase deposition. The obtained carbon-silver-gold nanostructures were characterized by high specific surface area and demonstrated high sensitivity as a material for surface-enhanced Raman scattering and adsorption properties allowing analyte extraction from a dilute solution for quantitative monitoring of low concentration components.

Synthesis of New Porphyrin-Fullerene Dyads Capable of Forming Charge-Separated States on a Microsecond Lifetime Scale.

A series of covalently linked axially symmetric porphyrin-fullerene dyads with a rigid pyrrolo[3,4-c]pyrrolic linker enabling a fixed and orthogonal arrangement of the chromophores has been synthesized and studied by means of transient absorption spectroscopy and cyclic voltammetry. The lifetime of the charge-separated state has been found to depend on the substituents on the porphyrin core, reaching up to 4 μs for a species with meso-(p-MeOC6H4) substituents. The ground and excited electronic states of model compounds have been calculated at the DFT and TD-DFT B3LYP(6-31G(d)) levels of theory and analyzed with regard to the effect of the substituent on the stabilization of the charge-separated state in the porphyrin-fullerene ensemble with a view to explaining the observed dependence.

Hybrid nanostructures: synthesis, morphology and functional properties

Hybrid nanostructures representing combinations of different materials and possessing properties that are absent in separate components forming the hybrid are discussed. Particular attention is given to hybrid structures containing plasmonic and magnetic nanoparticles, methods of their synthesis and the relationship between the composition, structure and properties. The functional features of the hybrid nanomaterials of various morphology (with core?shell structures, with encapsulated metal nanoparticles and with metal nanoparticles on the surface) are considered. The unique properties of these hybrid materials are demonstrated, which are of interest for solving problems of catalysis and photocatalysis, detecting impurities in various media, in vivo visualization, bioanalysis, as well as for the design of optical labels and multifunctional diagnostic nanoplatforms. The bibliography includes 182 references.

Direct laser writing of μ-chips based on hybrid C–Au–Ag nanoparticles for express analysis of hazardous and biological substances

Micro-chips based on organic-inorganic hybrid nanoparticles (NPs) composed of nanoalloys of gold (Au) and silver (Ag) embedded in an amorphous carbonaceous matrix (C-Au-Ag NPs) were prepared directly on a substrate by the laser-induced deposition (for short: LID) method. The C-Au-Ag NPs show a unique plasmon resonance which enhances Raman scattering of analytes, making the μ-chips suitable to detect ultra-low-volumes (10(-12) liter) and concentrations (10(-9) M) of bio-agents and a hazardous compound. These micro-chips constitute a novel, flexible solid-state device that can be used for applications in point-of-care diagnostics, consumer electronics, homeland security and environmental monitoring.

Laser-Induced Copper Deposition on the Surface of an Oxide Glass from an Electrolyte Solution

Continuous copper patterns were grown on the surface of oxide glass substrates through laserinduced chemical liquid-phase deposition (LCLD). The deposition was performed with the use of a continuouswave argon laser operating in a multimode regime. The deposition occurred as a result of the reducing chemical reaction initiated by laser radiation. Continuous metal patterns were produced by scanning focused laser radiation along the substrate-electrolyte interface. The morphology and the chemical composition of the deposited patterns were examined with the use of a CEM-SCAN 4 DV scanning electron microscope equipped with an energy-dispersive spectrometer. The morphology of the deposited patterns was investigated as a function of the laser radiation power and the number of scans. It was demonstrated that high-quality continuous patterns can be fabricated using one scan of the laser beam.

Laser-induced deposition of hetero-metallic structures from liquid phase

Laser-induced chemical-liquid phase deposition of hetero-metallic (Gu-Cr) structures is demonstrated for the first time. The deposition of hetero-metallic structures is of special interest thanks to wider range of properties as compared to pure metals. The deposition was realized from the electrolyte solution based on copper sulphate and potassium dichromate. The focused beam of the continuous wave Ar+ laser generated in the multiwave regime was used for the structures precipitation. The chemical processes resulting in Cu-Cr structures deposition are analyzed emphasizing some features typical for laser-assisted methods.

Ultrafast dynamics at lanthanide surfaces: microscopic interaction of the charge, lattice and spin subsystems

In solids the charge, lattice and spin degrees of freedom are coupled and the respective coupling strengths result in characteristic timescales on which excitations of one particular subsystem interact and equilibrate with the remaining subsystems. In ferromagnetic metals the respective elementary interaction processes occur on the pico- and femtosecond time scales. To elucidate these interaction mechanisms and the timescales we investigate the ultrafast dynamics of electrons, phonons and spins excited by an intense infrared optical pulse at Gd(0 0 0 1) and Tb(0 0 0 1) surfaces, employing complementary time-resolved methods of optical second harmonics generation and photoelectron spectroscopy. These surfaces exhibit rich dynamics including a collective response of the crystal lattice and the magnetization, manifested by a coupled coherent optical phonon–magnon mode at 3 THz. After a review of the earlier studies we present temperature- and fluence-dependent results of pump–probe experiments. The temperature dependence of the coherent phonon (CP) amplitude shows that a spin- and a charge-driven excitation mechanism can be separated. The spin-driven excitation dominates below the Curie temperature in agreement with ab initio model calculations that establish a displacement of the surface plane upon a change of the surface spin polarization. Analysis of the temperature-dependent CP damping shows an anomaly in the vicinity of the Curie temperature that is for Gd well described by phonon–magnon scattering. In the case of Tb an additional damping channel is required that could be related to local spin-flip excitations.