Yu. P. Piryatinski

Time-resolved photoluminescence spectroscopy of excitons in layered semiconductor PbI2 nanoclusters

We studied the dynamics of excitons excited in layered semiconductor PbI2 nanoclusters (NCLs) using time-resolved photoluminescence (TRPL) spectroscopy. TRPL spectra reveal formation of self-trapped excitons (STEs). It was shown that the formation of the STEs for larger [more than the Bohr radius of exciton in bulk PbI2 (RB = 1.9 nm)] NCLs occurs in sub-nanosecond time scale, while in the case of small NCLs with sizes about RB, it takes place in nanosecond scale. The effective energy transfer from the small to the larger semiconductor NCLs, which arises from dipole-dipole intercluster interactions, takes place in sub-nanosecond scale. We demonstrate that the STEs are stable states and they define effective radioluminescence of the investigated Pb1−XCdXI2 alloys.

Enhancement of Fluorescence of Porous Silicon upon Saturation by Liquid Crystal

The fluorescence of samples of porous silicon of various morphologies that are filled with a liquid crystal (LC), n-pentyl-n′-cyanobiphenyl (5CB), is studied. The fluorescence spectra of the sample, along with the long-wavelength band of porous silicon with a maximum in the range 627–667 nm, exhibit a short-wavelength band of 5CB with a maximum in the range 385–410 nm. The radiative relaxation times of porous silicon and 5CB lie in the micro- and nanosecond ranges, respectively. It is found that the filling of pores with 5CB enhances the fluorescence of porous silicon by two to three times. This enhancement is caused by non-radiative energy transfer from 5CB to the porous matrix as a result of efficient interactions between LC molecules and pore walls. Using IR spectroscopy, it is shown that the formation of hydrogen bonds between cyano groups of 5CB molecules and silanol groups of pore surface is the predominant type of these interactions. A transfer mechanism is suggested according to which excited associates of 5CB molecules transfer their energy via surface channels to excitons of porous silicon, enhancing its fluorescence.

Synthesis and Properties of Hybrid Poly(3-Methylthiophene)-CdSe Nanocomposite and Estimation of Its Photovoltaic Ability

We report the synthesis and properties of new hybrid nanocomposites of poly(3-methylthiophene) and CdSe nanoparticles. The synthesis method is based on the chemical oxidative polymerization of 3-methylthiophene in the presence of CdSe nanoparticles of different shapes (quantum dots, nanorods, and tetrapods). In situ, the open circuit potential and the UV-Vis monitoring of a reaction mixture are used to control the polymerization process. The minimal and maximal CdSe concentrations in nanocomposites are obtained for quantum dots and nanorods, respectively. Nanocomposites are investigated, by using IR, electronic absorption, and photoluminescence spectroscopies, TGA, and DTA. Hybrid photovoltaic (PV) cells based on these materials are fabricated and evaluated. The best PV performance is achieved for a device based on nanocomposites with CdSe nanorods.

Complexation in Composite Solutions of Melanin with 2,4,7-Trinitrofluorenone

A feasibility of formation of donor-acceptor charge-transfer (CT) complexes between melanin and 2,4,7-trinitrofluorenone (TNF) being good electron acceptor has been studied in solutions by means of the absorption and photoluminescence (PL) spectra. The model of electronic transitions in a melanin-TNF composite solution has been proposed.

Time-resolved photoluminescence spectroscopy of localized exciton magnetic polarons in Cd0.70Mn0.30Te spin glass compound

We have investigated dynamics of different localized exciton magnetic polarons (LEMPs) in Cd0.70Mn0.30Te spin glass (SG) compound below the freezing temperature Tf in the crystal regions, where various microscopic magnetic spin states (MMSSs), namely, “loose” spins, finite, and infinite clusters, are formed. It was shown that there is a broad distribution of the LEMPs lifetimes. The presence of the long-lived LEMPs is caused by the admixture of the optically active bright exciton states to the dark exciton states, i.e., the “brightening” of the dark LEMPs which exist along with the bright LEMPs. The lifetimes of the dark LEMPs correspond to hundreds of nanoseconds. It was found that the time decay of photoluminescence band intensity is approximated by the sum of two functions: a single exponential function and the Kohlrausch–Williams–Watts stretched exponential function. The stretched exponential function describes the recombination processes of the LEMPs formed in the crystal regions of the finite cluste...

Fluorescence properties of a composite material based on the 5CB nematic liquid crystal with gold nanoparticles

The steady-state and time-resolved fluorescence spectra of n-pentyl-n′-cyanobiphenyl and a related composite material with gold nanoparticles in the liquid crystalline and solid states have been investigated. The introduction of gold nanoparticles into the liquid crystal leads to a noticeable quenching of fluorescence in the emission region of the predimer and excimer states of cyanobiphenyl. In the solid phase, a quenching of free excitons and a short-wavelength shift of fluorescence bands have been observed.

Multiband light emission and nanoscale chemical analyses of carbonized fumed silica

Fumed silica with a specific area of 295 m2/g was carbonized by successive phenyltrimethoxysilane treatments followed by annealing in inert atmosphere up to 650 °C. Emission, excitation, kinetics, and photo-induced bleaching effects were investigated by steady state and time-resolved photoluminescence spectroscopies. The local chemistry was also studied by infrared transmission spectroscopy. Strong ultraviolet and visible photoluminescence was observed in the samples after the chemical treatments/modifications and thermal annealing. It has been shown that ultraviolet photoluminescence in chemically modified fumed silica is associated with phenyl groups, while near ultraviolet and visible emission in annealed samples originated from inorganic pyrolytic carbon precipitates dispersed in the silica host matrix. Two types of emission bands were identified as a function of the annealing temperature: one is in the near UV and the other is in the visible range. Based on the emission/excitation analysis of these two bands, as well as on correlations with the synthesis conditions, a structural-energy concept of light-emitting centers has been proposed. According to this model, the light-emitting centers are associated with carbon clusters that can be bonded or adsorbed on the silica surface. This has been validated by a detailed (S)TEM-electron energy-loss spectroscopy study, confirming the inhomogeneous distribution of nanoscale carbon precipitates at the surface of the silica nanoparticles. These carbon precipitates are mostly amorphous although they possess some degree of graphitization and local order. Finally, the fraction of sp2 carbon in these nanoclusters has been estimated to be close to 80%.Fumed silica with a specific area of 295 m2/g was carbonized by successive phenyltrimethoxysilane treatments followed by annealing in inert atmosphere up to 650 °C. Emission, excitation, kinetics, and photo-induced bleaching effects were investigated by steady state and time-resolved photoluminescence spectroscopies. The local chemistry was also studied by infrared transmission spectroscopy. Strong ultraviolet and visible photoluminescence was observed in the samples after the chemical treatments/modifications and thermal annealing. It has been shown that ultraviolet photoluminescence in chemically modified fumed silica is associated with phenyl groups, while near ultraviolet and visible emission in annealed samples originated from inorganic pyrolytic carbon precipitates dispersed in the silica host matrix. Two types of emission bands were identified as a function of the annealing temperature: one is in the near UV and the other is in the visible range. Based on the emission/excitation analysis of these t...

Dehydroacetic Acid Based Dioxaborine Styryl Dye: Effective Fluorescent Probe for Ammonia and Amine Detection

The newly synthesized dioxaborine dyes, derivatives of dehydroacetic acid, were tested for the detection of amines and ammonia. To discriminate the substance with efficient sensing parameters, series of ca. 20 dioxaborine dyes were synthesized and tested for reactivity with amines. The most promising one showed the fluorescent sensitivity to amines in the range of 1-4 ppm.

Effect of the Nature of the Template on the Structure and Properties of Electrodeposited Vertically Aligned Submicron ZnO Rods

The results of spectral (UV–vis), morphological (XRD, SEM), and current–voltage investigations of a nanostructured layer of ZnO electrodeposited on the surface of an ITO electrode are presented. The possibility of using tetraalkylammonium hydroxides (TAAH) as organic templates as an alternative to widely used templates such as eosin Y or coumarin was demonstrated for the first time. It was established that the spectral and electrophysical characteristics of the nanostructured ZnO layers synthesized in the presence of eosin Y and TAAH are close, which confirms the suitability of TAAH as template.

Electron correlations in crystals and molecules

An expression for the Green’s function of a disordered crystal is obtained with allowance for the electron-electron interaction. The electron states of the system are described in the framework of a multiband tight-binding model. The possibility of using the proposed approach for describing the energy spectrum of molecules is demonstrated in the limit of an infinitely large primitive cell of the crystal. The energy spectrum and effective charges of atoms of a tricyanobutadienecarbazole molecule are calculated.