Alentsev Fock Method Research Articles

The components of 630-nm band in ZnSe and their recombination mechanisms

A non-elemental luminescence band with a maximum at 630 nm was studied in the undoped ZnSe crystals. This broad luminescence band was expanded into components by the Alentsev-Fock method, and the two basic elemental components were identified at room temperature. For these elemental components, mechanisms of recombination were established by comparing the temperature dependences of the luminescence intensity at different wavelengths. These components were named: D+–band (hvmax= 1.875 eV, 661 nm, δ = 0.181 eV) with the hole recombination mechanism and D––band (hvmax= 2.028 eV, 611 nm, δ = 0.196 eV) with the electron recombination mechanism.

ANALYSIS OF THE SEPARATION METHODS OF OPTICAL SPECTRA FOR INDIVIDUAL COMPONENTS

A comparative analysis of various methods for the decomposition of broad bands into individual components has been carried out. It is shown that the most universal are the methods of modulation spectroscopy and direct differentiation of conventional spectral characteristics, which, unlike the widely used Alentsev-Fock method, are applicable to spectra of any type (luminescence, transmission, absorption, etc.). The features and capabilities of the direct differentiation method are used to identify the structure in the emission spectra and transmission of ZnSe <Al> single-crystal substrates.

Spectro-Electro-Gravimetry of Poly (o-toluidine)

Polyaniline and derivatives are one of ICPs most investigated [1-4]. Despite the considerable advances on the knowledge of the electrochemical reactions in this family of ICPs, it is still generally assumed that a “simple” transition from insulating form (leucoemeraldine or LE) to conductor form (emeraldine or E) by anion doping takes place with the formation of polaron centers [5]. Nekrasov et al and Hillman et al have proven that this transition is more complex than assumed or discussed in literature. On the one hand, Hillman et al have suggested a slow-moving solvent counter flux with a fast anion insertion together with a proton expulsion during this transition, at least, in HClO4 solution [6,7]. On the other hand, Nekrasov et al have proven that two different species are generated and coexist during this transition: (i) the isolated polarons or radical cations (P*) with a spectral response around 420 nm and the (ii) the conducting polarons which are coil structures due to the strong interaction of anions with the C-NH+-C group (PC) with a spectral response around 840 nm [8-10]. We present a more detailed electrochemical mechanism for the insulating to conductor transformation of POT films. During the relaxation, protons are expulsed when the isolated polarons (P*) detected at 420 nm are oxidized. Isolated polarons could be formed because of trapped anions when the film is reducing and shrinking (packing). Anions are inserted during the formation of conducting polarons (PC), which consist in coil structures due to the strong interaction of anions with the C-NH+-C group of polymer detected at 840 nm. [1] A. Syed, M. Dinesan, Polyaniline - a Novel Polymeric Material - Review, Talanta. 38 (1991) 815–837. doi:10.1016/0039-9140(91)80261-W.[2] T.H. Qazi, R. Rai, A.R. Boccaccini, Tissue engineering of electrically responsive tissues using polyaniline based polymers: A review, Biomaterials. 35 (2014) 9068–9086. doi:10.1016/j.biomaterials.2014.07.020.[3] R.Y. Suckeveriene, E. Zelikman, G. Mechrez, M. Narkis, Literature review: conducting carbon nanotube/polyaniline nanocomposites, Reviews in Chemical Engineering. 27 (2011) 15–21. doi:10.1515/REVCE.2011.004.[4] J. Lai, Y. Yi, P. Zhu, J. Shen, K. Wu, L. Zhang, J. Liu, Polyaniline-based glucose biosensor: A review, Journal of Electroanalytical Chemistry. 782 (2016) 138–153. doi:10.1016/j.jelechem.2016.10.033.[5] G. Ćirić-Marjanović, Recent advances in polyaniline research: Polymerization mechanisms, structural aspects, properties and applications, Synthetic Metals. 177 (2013) 1–47. doi:10.1016/j.synthmet.2013.06.004.[6] M.J. Henderson, A.R. Hillman, E. Vieil, Ion and Solvent Transfer Discrimination at a Poly(o-toluidine) Film Exposed to HClO4 by Combined Electrochemical Quartz Crystal Microbalance (EQCM) and Probe Beam Deflection (PBD), J. Phys. Chem. B. 103 (1999) 8899–8907. doi:10.1021/jp9910845.[7] M. J. Henderson, A. Robert Hillman, E. Vieil, A combined electrochemical quartz crystal microbalance (EQCM) and probe beam deflection (PBD) study of a poly(o-toluidine) modified electrode in perchloric acid solution, Journal of Electroanalytical Chemistry. 454 (1998) 1–8. doi:10.1016/S0022-0728(98)00245-9.[8] A.A. Nekrasov, V.F. Ivanov, A.V. Vannikov, Analysis of the structure of polyaniline absorption spectra based on spectroelectrochemical data, J. Electroanal. Chem. 482 (2000) 11–17. doi:10.1016/S0022-0728(00)00005-X.[9] A.A. Nekrasov, V.F. Ivanov, A.V. Vannikov, Effect of pH on the structure of absorption spectra of highly protonated polyaniline analyzed by the Alentsev-Fock method, Electrochimica Acta. 46 (2001) 4051–4056. doi:10.1016/S0013-4686(01)00693-4.[10] A.A. Nekrasov, V.E. Ivanov, O.L. Gribkova, A. Vannikov, Voltabsorptometric study of “structural memory” effects in polyaniline, Electrochimica Acta. 50 (2005) 1605–1613. doi:10.1016/j.electacta.2004.10.030. Part of this work was supported by MINECO-FEDER CTQ2015-71794-R.

Photoluminescence Properties of β-Ga2O3 Thin Films Produced by Ion-Plasma Sputtering

Photoluminescence and photoexcitation spectra of β-Ga2O3 thin films prepared by high-frequency ion-plasma sputtering in an Ar atmosphere were investigated. Photoluminescence spectra were deconvoluted by the Alentsev—Fock method into ultimate constituents. The nature of two strong bands with maxima at 2.95 and 3.14 eV and two weak bands with maxima at 3.90 and 4.25 eV was discussed. The two strong bands were attributed to an associate originating from the interaction of oxygen and gallium vacancies; the weak ones, recombination of excitons in quantum wells formed by acceptor clusters. It was found that the damping time constant for the 3.14-eV band was 105 μs; for the 2.95-eV band, 114 μs. The similarity of the decay time constants for these bands confirmed their relationship to a common associate.

The Luminescent Centra in thin Films of β–Ga2O3 and (Y0.06Ga0.94)2O3

Photoexcitation and photoluminescence spectra of b–Ga2O3 and (Y0.06Ga0.94)2O3 thin films obtained by high-frequency ion-plasmous sputtering was investigated. Luminescence spectra were factorized on ultimate constituents using Alentsev-Fock method. The nature of two intensive luminescent band with maxima in region 3.00 and 3.15 eV and two faint intensive luminescent band with maxima in region 4.00 and 4.25 eV was discussion. Luminescence decay time for band with maximum in region 3.00 and 3.15 eV in different types of b–Ga2O3 and (Y0.06Ga0.94)2O3 thin films was established.

Luminescence Centers in Thin Films of ZnGa2O4

Photoexcitation spectra and luminescence of thin films of ZnGa2O4 under photo-, cathode and X-ray excitation were investigated. Luminescence spectra were factorized on ultimate constituents using Alentsev-Fock method. Emission bands with maximums at 3.35, 2.85, 2.50 and 2.38 eV were referred to the luminescence at the expense of electronic transitions between 4Т2, 4Т1, 2Е and 4А2 terms in octahedral complexes (GaO6)9–. It was proposed an energy level diagram with corresponding electronic transitions in such structure. Luminescence band with maximum at 1.75 eV is attributed to oxygen vacancies.

Luminescence centers in bismuth-containing oxytungstate ceramics

We have studied the photoexcitation and luminescence spectra of Bi2WO6, Y2WO6 and Y2WO6:Bi ceramics. We used the Alentsev-Fock method to decompose the spectra into elementary components. The emission bands with maximum at 2.93 eV in the luminescence spectrum of Bi2WO6, 3.02 eV in the luminescence spectrum of Y2WO6, and 2.95 eV in the luminescence spectrum of Y2WO6:Bi are assigned to luminescence of self-localized Frenkel excitons. The bands with maxima at 2.35 eV and 1.90 eV in the spectrum of Bi2WO6, 2.25 eV and 1.75 eV in the spectrum of Y2WO6, and 2.35 eV and 1.85 eV in the spectrum of Y2WO6:Bi are connected with oxygen vacancies.

Voltabsorptometric study of “structural memory” effects in polyaniline

This study is aimed at clarifying the role of the counter anions used in the electrochemical synthesis of polyaniline (PAn) on the spectroelectrochemical properties of the resulting film (so-called “structural memory” effect). Polyaniline films were synthesized in aqueous solutions of different acids: HCl, HClO 4 and H 2SO 4 (‘parent’ acids). Further spectroelectrochemical studies were performed in aqueous solutions of the above-mentioned acids for each of the films synthesized in the above ‘parent’ acids. Differential voltabsorptometric curves (d A/d t versus potential (DCVA)) were measured at certain characteristic wavelengths corresponding to the individual absorption bands separated from the spectra using Alentsev–Fock method. These are the bands of the radical cations (435 nm), quinoid fragments (570 nm), dimers of radical cations (presumably 665 nm) and ‘localized polarons’ (755 nm). Particular attention has been paid to the formation of the dimers of radical cations and their role in the redox transitions in the film. Comparing our results with the literature data, we suppose that such dimers may facilitate electron exchange between adjacent polymer chains contributing to the conductivity increase. Complex nature of the first voltammetric peak was discovered, which is probably due to the heterogeneous structure of PAn. Results of molecular modeling of the interchain dimers of the radical cations using semi-empirical PM3 calculations are reported and their electronic spectrum was simulated.

Luminescence of Thin Bi2W2O9Films

The luminescence spectra of thin Bi2W2O9 films have been investigated. The spectra were separated into elementary components by the Alentsev–Fock method. The radiation band with a maximum at 2.43 eV in the luminescence spectrum of Bi2W2O9 has been assigned to the Frenkel autolocalized excitons. The luminescence bands with maxima at 2.10 and 1.90 eV have been assigned to the emission of the centers whose energy levels are located in the forbidden band. The luminescence of the Bi2W2O9 films is due to the emission of the WO6 complex.

Luminescence of Bismuth‐Activated Ceramics of Yttrium and Scandium Oxides

The luminescence spectra of Y2O3:Bi and Sc2O3:Bi ceramics have been investigated. The spectra have been resolved into elementary components by the Alentsev–Fock method. It has been established that the luminescence is attributed to emission centers of three types, two of which are due to the replacement of Y3+ (or Sc3+) by Bi3+ at the nodes of the crystal lattice of Y2O3 (or Sc2O3) with the point symmetry C2 and C3i. The emission center Bi3+ in the position C3i leads to the appearance of blue luminescence with maxima at 3.03 eV for Y2O3:Bi and at 3.05 eV for Sc2O3:Bi; this luminescence is attributed to the transition 3P1–1S0. The emission center Bi3+ in the position C2 initiates green luminescence (which is also related to the 3P1–1S0 transition in Bi3+) with a maximum in the region of 2.40 eV in Y2O3:Bi and in the region of 2.46 eV in Sc2O3:Bi. The red luminescence band with maxima at 1.85 eV in Y2O3:Bi and at 1.95 eV in Sc2O3:Bi is related to the presence of structural defects.

Effect of pH on the structure of absorption spectra of highly protonated polyaniline analyzed by the Alentsev–Fock method

This paper presents the results of the investigation of the effect of pH of highly acidic medium (pH 0 and 1) on the structure of the electronic spectra of polyaniline films in the spectral range 300–900 nm. The analysis was carried out using the Alentsev–Fock method, which requires no preliminarily notion about the possible shape and/or number of the individual absorption bands and extensive statistical calculations. Along with the six absorption maximums described earlier by other authors three new individual bands were separated. On the basis of the comparison of our results with the literature data, we are inclined to assign the new band near 530–570 nm (depending on the pH) to the donor–acceptor interaction between the quinoid fragments and the counter anions and the new band at λ max>900 nm to the ‘free carriers’ absorption. We also suppose that the new band near 810–830 nm may be associated with the second absorption band of the cation-radical dimers. The effect of an increase in pH on the structure of polyaniline absorption spectra manifests itself in the increase of the portions of the bands corresponding to different electron transitions in the quinoid fragments, as well as in the decrease of the portions of the bands related to the conductivity of the film (i.e. the bands of the cation-radical dimers (or polarons) and free charge carriers).

A comparative voltabsorptometric study of polyaniline films prepared by different methods

A comparative cyclic voltabsorptometric study was carried out for polyaniline (PAn) films prepared by electrochemical polymerization and vacuum thermal evaporation. The absorption values were measured at different characteristic wavelengths (895, 755, 665, 435, and 325 nm) corresponding to the individual absorption bands separated by us earlier from the spectra using the Alentsev–Fock method. Differential voltabsorptometric curves (d A/d t vs. potential (DCVA)) measured in aqueous HCl were compared with ordinary cyclic voltammetry (CVA). The experiments for different sweep rates were also compared. It was found that the DCVA peak at 895 nm corresponds perfectly to the CVA peak both in the electrosynthesized and the vacuum deposited PAn. The DCVA peak at 435 nm (cation-radicals) precedes the CVA peak (similar to the maximum of the EPR signal), while that at 755 nm (polarons or cation-radical dimers) lags behind the CVA peak. For the vacuum deposited films an intense intermediate DCVA and current peaks (at about 0.6 V vs. Ag/AgCl) are observed. The results are discussed in terms of the heterogeneous structure of PAn; particularly, its specific features in the films prepared using different methods.

Luminescence centers in ceramics of yttrium, scandium, and bismuth oxytungstates

An investigation is made of the luminescence spectra of Me2WO6 ceramics (Me=Y, Sc, Bi). The spectra were decomposed into elementary components by the Alentsev—Fock method. Radiation hands with a maximum at 3.02 eV in the Y2WO6 luminescence spectrum, at 2.8 eV in the ScWO6 spectrum, and at 2.93 eV in the Bi2WO6 spectrum are assigned to the light emission of self-localized Frenkel excitons. The bands with maxima at 2.25 and 1.75 eV in the Y2WO6 spectrum, at 2.36 and 1.9 eV in the Sc2WO6 spectrum, and at 2.35 and 1.9 eV in the Bi2WO6 spectrum are related to oxygen vacancies.

Analysis of the structure of polyaniline absorption spectra based on spectroelectrochemical data

Abstract Using the results of spectroelectrochemical experiments (absorption spectra measured at different stationary potentials from 0.0 to 0.8 V versus Ag | AgCl) performed in aqueous acidic medium for polyaniline (PAN) films electrochemically deposited onto SnO2-glass substrates, individual absorption bands composing the spectra were analyzed. The key point of the method used for separation of the individual bands (Alentsev–Fock method) is that one need not have a preliminary notion about real shape, number and positions of individual components of the spectrum. The necessary conditions are the following: (1) in the most common case, the number of spectra used for separation should be equal to or exceed the number of possible components; (2) the spectra should contain different proportions of the individual bands. Both well-known (cation-radicals (near 435 nm), localized polarons (near 755 nm), quinoid structures (near 665 nm)) and some new absorption bands were found. Comparing these results with our earlier data for electrochemically deposited and vacuum evaporated PAN films in different acidic media, the newly revealed band near 570 nm may be attributed to donor–acceptor interaction of quinoid fragments of the polymer chain with counter anions. The band in the NIR region (>900 nm), which is often referred to as that of ‘free carriers’, apparently characterizes electron exchange between highly conductive areas of the film.

Spectral energy characteristics of 6,γ- and 7,γ-dimethyl ethers of chlorine 6 in water-alcohol solutions

Absorption spectra and dispersion of optical rotation (DOR) are measured for monomers of 6,γ- and,7,γ-dimethyl ethers of chlorin e6 (Ch-6,γ-DME and Ch-7,γ-DME) in 96% ethanol and for associates of them that are polymers and colloidal particles. The optical activity of Ch-6,γ-DME monomers is higher than that of Ch-7,γ-DME monomers, which is linked with more pronounced distortion of the molecular macrocycle for Ch-6,γ-DME in the γ-C6 local region. The structural and energy parameters of dimeric unit cells of Ch-6,γ-DME and Ch-7,γ-DME polymers are discussed from the standpoint of the Davydov-Tinoko exciton theories. Longwave absorption spectra and DOR are resolved into individual components with the aid of a modified Alentsev-Fock method.

Luminescence centers in yttrium silicate and germanate

Luminescence spectra for isostructural Y2SiO5 and Y2GeO5 are investigated. The spectra are resolved into elementary components by the Alentsev—Fock method. Bands with maxima in regions of 2.6, 2.3, and 2.05 eV in the spectra of Y2SiO5 luminescence and in regions of 2.55, 2.25, and 2.0 eV in the spectra of Y2GeO5 luminescence are considered as radiative recombination of excited associative donor-acceptor Y3+−O2− pairs. The indicated bands are related to certain distances between yttrium (the donor) and oxygen (the acceptor). A band with a maximum of 2.95 eV in Y2SiO5 and 3.0 eV in Y2GeO5 occurs in recombination of electrons with holes trapped by an anionic sublattice.

Luminescence centers in thin films of lead and bismuth tungstates

Luminescence spectra of thin films of PbWO4 and Bi2WO6 are invesigated. The Alentsev-Fock method is used to separate the spectra into elementary components. The emission bands with maxima at 2.8 eV in PbWO4 and at 2.93 eV in Bi2WO6 luminescence spectra are interpreted as the emission of self-localized Frenkel excitons. The bands with maxima at 2.35 and 1.75 eV in PbWO4 and at 2.35 and 1.9 eV in Bi2WO6 are related to oxygen vacancies.

Luminescence centers in Sc2O3

Sc2O3 luminescence spectra are studied. The spectra are separated into elementary bands by the Alentsev–Fock method. It is established that the luminescence spectra consist of a number of overlapping bands with maxima at 3.5; 3.05; 2.65; 2.35, and 2.05 eV. The band at 3.5 eV is interpreted as emission of self-localized excitons, and the other bands, as defect-center recombination.