Valerij S. Gurin

Nonlinear optical properties of CuxS and CuInS2 nanoparticles in sol–gel glasses

Silica glasses with ultrafine CuxS and CuInS2 particles (average radius of 5±3 nm) were fabricated by means of a sol–gel technique. Linear and differential absorption spectra were studied. The glasses reveal absorption peaks in the 600–700 nm range associated with the first excitonic resonance in the quantum confined particles. Laser excitation by 540 nm pulses leads to the induced absorption effect in the 480–980 nm spectral range. The relaxation of the induced absorption has a time constant equal to about 500 ps for CuS-doped glasses and a biexponential type (with τ1≈30 ps and τ2>1 ns) for CuInS2-doped ones.

Metal clusters and nanoparticles assembled in zeolites: an example of stable materials with controllable particle size

Abstract An ion-exchangeable zeolite (mordenite) is used to control the formation of nanoparticles and clusters within the solid matrix by the hydrogen reduction of metal ions (Ag+, Cu2+, and Ni2+). SiO2/Al2O3 molar ratio in mordenite appears to be an efficient tool to manage the reducibility of the metal ions. Few-atomic silver clusters in line with the larger silver nanoparticles were observed with DRS for the reduced Ag+-exchanged mordenites. Cu2+-exchanged ones produce the copper nanoparticles with different optical appearance, and Ni2+-exchanged mordenites are reduced up to complicated species with no explicit assignment of metal particles under the conditions studied.

Picosecond absorption spectroscopy of surface modified copper sulfide nanocrystals in polymeric film

The transient induced absorption and bleaching are examined in 10 nm size CuS nanocrystals embedded in polyvinylalcohol film. Partial surface oxidation of CuS nanocrystals produces a new near‐IR‐absorption band peaked at 1100 nm. The surface oxidized shell is supposed to form a midgap electron acceptor level and the near‐IR band relates to the electron transfer from the CuS valence band. The near‐IR band is bleached easily by 15 ps pump pulse from YAG:Nd laser (1.08 μm). The bleaching is accompanied by the induced absorption at the red side of CuS fundamental edge. Both signals induced decay quickly with the time constant 65–70 ps. The model is proposed where the electron–hole pair excited by near‐IR photon (electron in surface shell and hole inside CuS core) creates strong internal electric field, which induces the Stark red shift of CuS fundamental edge.

Nonlinear optical properties and laser applications of copper chalcogenide quantum dots in glass

Absorption saturation and picosecond pump-probe measurements on oxidized copper selenide quantum dots in sol-gel glasses were carried out. The bleaching relaxation time was found to be ∼300 ps. The saturation intensities were estimated to be 2.2 MW/cm 2 at 1.06 μm and 7 MW/cm 2 at 1.54 μm for Cu 2 Se and Cu 2+x Se-doped glasses, respectively. Passive Q-switching of 1.06, 1.34, and 1.54 μm solid state lasers with copper selenide-doped glasses as saturable absorbers were demonstrated.

Formation of ultrafine particles of copper and copper sulfide in silica films and glasses prepared by sol–gel technique

Abstract The preparation, composition and optical properties of silica films and glasses produced by the sol–gel technique with incorporated copper compounds have been studied. Heat treatment of the samples in hydrogen or hydrogen sulfide results in a chemical transformation of copper oxide particles into small copper particles or copper sulfide particles, respectively. Optical absorption of samples with the different copper compounds have been measured in UV, visible and near IR regions and features in the observed absorption spectra are briefly discussed.

Self-assembling of silver and copper small clusters within the zeolite cavities: prediction of geometry

Abstract The factors affecting a self-assembling of certain kind of silver and copper clusters during reduction of ion-exchanged forms of zeolites in hydrogen were studied. Conditions leading to the preferable M8 cluster formation were revealed. A matching of zeolite void and cluster sizes was found to be the key factor facilitating this process. Ag8 clusters can be easily stabilized in the zeolites with certain pore size (a cross-section in the range of 0.63–0.67 nm). Zeolites possessing voids wider than 0.70 nm stabilize these clusters only for low reduction temperatures. Small pores possessing at least one axis of pore cross-section ≤0.63 nm do not stabilize Ag8 clusters. Cu clusters assigned to Cu8 were predicted to be formed in narrow pores of erionite much easier than in mordenite voids. Comparison of experimental UV–Vis spectra with the results of ab initio calculations for selected M8 isomers was performed. The difference between Ag8 and Cu8 cluster models is discussed.

Sol–gel silica glasses with nanoparticles of copper selenide: synthesis, optics and structure ☆

Abstract The silica glasses with copper selenide nanoparticles were fabricated by the sol–gel technique. The samples were characterized with transmission electron microscopy, Rutherford backscattering spectroscopy and optical absorption. The composition of nanoparticles is close to Cu 2 Se stoichiometry and can be varied under tuning of the preparation steps. These glasses exhibit the new features in visible and IR ranges.

Nonlinear optical properties of solgel-derived glasses doped with copper selenide nanoparticles

Transient differential absorption spectra of solgel glasses that contain copper selenide nanoparticles (NP’s) have been studied with a picosecond pump–probe technique. Oxidation of copper selenide NP’s results in the appearance of an additional absorption band peaked at ∼1 µm, which can be transiently bleached under laser excitation. Excited-state absorption related to mid-gap surface trap states was observed. The absorption recovery time was found to be ∼300 ps. The intensity-dependent transmission of oxidized copper selenide NP’s in solgel glass at 1.08 µm has been measured. Permanent laser-induced absorption changes in the glasses were studied with nanosecond pulses as a function of laser exposure. Passive Q switching of 1.06-µm Nd3+:Y3Al5O12, 1.34-µm Nd3+:YAlO3, and 1.54-µm Er3+: glass lasers has been realized with the glasses containing copper selenide NP’s used as saturable absorbers. Q-switched pulses with 100-ns (1.06 µm), 90-ns (1.34 µm), and 60-ns (1.54 µm) pulse widths were obtained.

Nonlinear properties of phototropic media on the basis of CuxSe nanoparticles in quartz glass

Energy and kinetic characteristics of theinduced transparency in quartz sol-gel glasses containing copper selenide nanoparticles of different stoichiometry are studied. The dependence of the nonlinear optical properties of the glass samples on the chemical composition of copper selenide particles, which gives rise to an additional absorption band in the near-infrared region and determines its spectral position, is established. It is found that the time of relaxation of the induced transparency increases and the peak absorption cross section decreases as the absorption maximum shifts to the low-energy spectral region.

Surface segregation of transition metals in sol-gel silica films

Silica sol-gel films (SGFs) doped with various transition metals derived by spin-coating on glass substrates and silicon wafers have been studied. Precursor solutions were prepared by mixing tetraethylorthosilicate, ethanol, water and nitrates of the transition metals (Cr, Mn, Fe, Co, Ni and Cu) using HCl as a catalyst. Remarkable segregation of metals at the surface was observed for films doped with Cu and Co. For Mn- and Ni-doped films this effect was much less, and it vanished for the films doped with Cr or Fe. The influence of boron and phosphorus upon the chemical state and the distribution of metal atoms was also analysed. The structure, optical properties and composition of the SGFs were studied and some pathways to control the dopant segregation effect were realized.