Exciton-phonon interaction in Y2O3 and Sc2O3 thin films

An investigation is made of the fundamental absorption edge of Y₂O₃ thin films. Based on its temperature dependence the exciton-phonon interaction is studied, which makes it possible to interpret the absorption edge as the absorption of self-localized excitons. A number of parameters of the energy spectrum of the investigated films are determined. I. Franko State University, 50, Dragomanov St., L'vov, 290005, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 1, pp. 132–134, January–February, 1999.     

Optical absorption edge of As<Subscript>40–<Emphasis Type="Italic">x</Emphasis></Subscript>Sb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>S<Subscript>60</Subscript> glassy alloys

The fundamental absorption edge of glassy alloys of an As–Sb–S system was studied in the temperature range 77–300 K. The spectral and thermal behavior of the fundamental absorption edge of As_40–x Sb_xS₆₀ glasses was shown to be described by an exponential function of phonon energy. The temperature and concentration behavior of the optical band gap in the studied glasses was established. The well-known Varshni relationship was used to describe the temperature dependence of the optical band gap.     

Photostimulated transformations of radiation color centers of SrCl2−Ce crystals

Spectra of x-ray radiation-induced absorption of SrCl₂−Ce crystals in the region of 340–830 nm under the effect of selective irradiation in the induced-absorption bands by both conventional and laser sources are investigated. It is established that irradiation of sufficient intensity causes irreversible photochemical transformations of PC, PC⁺, and Ce²⁺ color centers their destruction, and restoration of the transparency of the crystals. To whom correspondence should be addressed. I. Franko Lvov State University, 8, Kirill and Mefodii Str., Lvov, 290005, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 5, pp. 666–668, September–October, 1999.     

Optical absorption in layered MnGaInS<Subscript>4</Subscript> single crystals

Optical absorption in MnGaInS₄ single crystals has been studied. Direct and indirect optical transitions are found to occur in the range of photon energies of 2.37–2.74 eV and in the temperature range of 83–270 K. The temperature dependence of the band gap has been determined; its temperature coefficients E _gd and E _gi are −5.06 × 10⁻⁴ and −5.35 × 10⁻⁴ eV/K, respectively. MnGaInS4 single crystals exhibit anisotropy in polarized light at the absorption edge; the nature of this anisotropy is explained.     

Optical and Photoelectric Properties of CuGa<Subscript>5</Subscript>Te<Subscript>8</Subscript> Single Crystals and In/<Emphasis Type="Italic">p</Emphasis>-CuGa<Subscript>5</Subscript>Te<Subscript>8</Subscript> Structures

The transmission spectra of CuGa₅Te₈ single crystals grown by the Bridgman method at temperatures of 10–300 K have been measured in the region of their intrinsic absorption edge. The energy-gap width of CuGa₅Te₈ single crystals has been determined, and its temperature dependence has been constructed. Photosensitive, surface-barrier In/p-CuGa₅Te₈ structures were formed for the first time on the basis of the indicated single crystals, and their photoelectric properties were investigated. It is shown that these structures can be used as broad-range photodetectors of natural radiation. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 4, pp. 514–518, July–August, 2005.     

Temperature dependence of the bandgap width in FeIn2Se4 single crystals

We have used the Bridgman method to grow single crystals of the ternary compound FeIn₂Se₄ and we have determined their composition and structure. We measured the transmission spectra in the intrinsic absorption edge region in the temperature range 20–300 K. From the transmission spectra, we determined the bandgap width and plotted its temperature dependence. We show that the E_g(T) dependence has a shape typical for semiconductor compounds.     

Vibrational spectra of thin eulytine films

This is a study of IR reflection spectra of systems of a thin Bi₄X₃O₁₂(X=Si, Ge) film and a substrate of fused quartz v-SiO₂ in the range 400–1600 cm⁻¹ at T=295 K. Bands assigned to Bi₄X₃O₁₂ are interpreted. It is found that single-photon processes are exhibited in the range 400–800 cm⁻¹, while biphonon processes, in the range 800–1600 cm⁻¹. I. Franko State University of Lvov, 50 Dragomanov St., 290005, Lvov, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 4, pp. 494–498, July–August, 1997.     

Thermal ionization of impurity centers in Fe-doped Bi12SiO20 and Bi12GeO20 crystals

The spectral and temperature dependence of the optical absorption and thermally stimulated depolarization currents in Fe-doped Bi₁₂SiO₂₀ and Bi₁₂GeO₂₀ crystals are investigated in the photon energy range 1.36–3.46 eV and temperature 85–750 K. The results show thermally induced electron redistribution between donor and acceptor levels and defect association-dissociation processes and are discussed using the configuration-coordinate model. Fiz. Tverd. Tela (St. Petersburg) 41, 1006–1011 (June 1999)     

Fundamental Absorption Edge of Thin PbWO4 Films

Based on the temperature dependence of the fundamental absorption edge of thin PbWO₄ films, we studied the exciton–phonon interaction, which made it possible to interpret the absorption edge as the absorption of autolocalized excitons. The temperature dependence of the forbidden band gap is investigated.     

Anharmonicity and superconductivity in Ba0.6K0.4BiO3

The temperature dependence of the x-ray absorption spectra above the L ₃ absorption edge of bismuth in the superconducting oxide Ba_0.6K_0.4BiO₃ are investigated. It is found that the local structure is different from the simple cubic structure indicated by x-ray and neutron-diffraction data. It is shown that the oxygen atoms move in an anharmonic double-well potential arising as a result of the existence of two nonequivalent types of octahedral environments of bismuth. Vibrations in such potential modulate the Bi-O bond lengths at the low frequency of the rotational (“tilting” type) mode of the oxygen octahedra and thus give rise to a strong electron-phonon interaction, which explains the quite high superconducting transition temperatures T _c ∼30 K. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 12, 977–982 (25 June 1998)     

Nature of optical properties of GdFe3(BO3)4 and GdFe2.1Ga0.9(BO3)4 crystals and other 3d5 antiferromagnets

Influence of the partial substitution of paramagnetic Fe³⁺ ions by diamagnetic Ga³⁺ ions in the trigonal crystal GdFe₃ (BO₃)₄ on its optical and magnetic properties is studied and discussed in connection with problems common for all antiferromagnets containing 3d ⁵ ions. Polarized optical absorption spectra and linear birefringence of GdFe₃ (BO₃)₄ and GdFe_2.1Ga_0.9 (BO₃)₄ single crystals have been measured in the temperature range 85–293 K. Specific heat temperature dependence (2–300 K) and structure of GdFe_2.1Ga_0.9 (BO₃)₄ crystal have been also studied. As a result of substitution of 30% Fe to Ga the Neel temperature diminishes from 38 till 16 K, the strong absorption band edge shifts on 860 cm^-1 (0.11 eV) to higher energy and the d-d transitions intensity decreases substantially larger than the Fe concentration does. Strong absorption band edge is shown to be due to Mott-Hubbard transitions. Correlation between position of the strong absorption band edge and the Neel temperature of antiferromagnets has been revealed. Properties of the doubly forbidden d-d transitions in the studied crystals and in other antiferromagnets are explained within the framework of the model of the exchange-vibronic pair absorption, which is theoretically analyzed in detail. The model permitted us to determine the connection between parameters of d-d absorption bands (intensity, width and their temperature dependences), on the one hand, and the exchange, spin-orbit and electron-lattice interactions, on the other hand.     

Optical absorption and exciton-phonon interaction in solid solutions Cu<Subscript>6</Subscript>PS<Subscript>5</Subscript>I<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Cl<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

We have studied the optical absorption edge of solid solutions Cu₆PS₅I_{1 − x} Cl _x at high absorption levels in the temperature range of 77–320 K. In a superionic state, we have revealed the Urbach behavior of the absorption edge, determined its parameters, and studied their temperature and concentration variations. We consider exciton-phonon interaction as a mechanism by which the Urbach bundle is formed and show that this bundle can be described in terms of the Dow-Redfield model.     

Electrical,optical, and structural characterization of polymer blend (PVC/PMMA) electrolyte films

Ion-conducting solid polymer blend electrolytes based on polyvinyl chloride (PVC)/poly methyl methacrylate (PMMA) complexed with sodium perchlorate (NaClO₄) were prepared in various concentrations by solution cast technique. The features of complexation of the electrolytes were studied by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. DC conductivity of the films was measured in the temperature range 303–398 K. Transference number measurements were carried out to investigate the nature of charge transport in the polymer blend electrolyte system. The electrical conductivity increased with increasing dopant concentration, which is attributed to the formation of charge transfer complexes. The polymer complexes exhibited Arrhenius type dependence of conductivity with temperature. In the temperature range studied, two regions with different activation energies were observed. Transference number data showed that the charge transport in this system is predominantly due to ions. Optical properties like absorption edge, direct band gap, and indirect band gap were estimated for pure and doped films from their optical absorption spectra in the wavelength region 200–600 nm. It was found that the energy gap and band edge values shifted to lower energies on doping with NaClO₄ salt. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamil Nadu, India, Dec. 7–9, 2006.     

Spectroscopy of Sm3+ activator centers in Ca3Ga2Ge4O14 single crystals

Results of investigations of spectroscopic properties of Ca₃Ga₂Ge₄O₁₄ single crystals activated with Sm³⁺ ions are reported. It is shown that Sm³⁺ ions in Ca₃Ga₂Ge₄O₁₄ form a type of activator quasicenter whose nature is associated with disordering of the matrix. I. Franko Lvov State University, 50, Dragomanov St., Lvov, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 2, pp. 296–298, March–April, 1998.     

Dynamics of femtosecond-laser-ablated liquid-aluminum nanoparticles probed by means of spatiotemporally resolved X-ray absorption spectroscopy

We investigated spatiotemporal evolution of expanding ablation plume of aluminum created by a 100-fs, 10¹⁴–10¹⁵-W/cm² laser pulse. For diagnosing dynamic behavior of ablation plume, we employed the spatiotemporally resolved X-ray absorption spectroscopy (XAS) system that consists of a femtosecond-laser-plasma soft X-ray source and a Kirkpatrick–Baez (K–B) microscope. We successfully assigned the ejected particles by analyzing structure of absorption spectra near the L _II,III absorption edge of Al, and we clarified the spatial distribution of Al⁺ ions, Al atoms, and liquid droplets of Al in the plume. We found that the ejected particles strongly depend the irradiated laser intensity. The spatial distribution of atomic density and the expansion velocity of each type of particle were estimated from the spatiotemporal evolution of ablation particles. We also investigated a temperature of the aluminum fine particles in liquid phase during the plume expansion by analyzing the slope of the L _II,III absorption edge in case of 10¹⁴-W/cm² laser irradiation where the nanoparticles are most efficiently produced. The result suggests that the ejected particles travel in a vacuum as a liquid phase with a temperature of about 2500 to 4200 K in the early stage of plume expansion.     

Transmission spectra of films of Mn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se solid solutions

Films of Mn_1−x Fe _x Se (x = 0–0.45) solid solutions were flash-sputtered. We measured the transmission spectra of the films in the wavelength range 200–1000 nm at room temperature. From these spectra, we calculated the absorption coefficients and determined the fundamental absorption edge, the position of which is shifted from 2.65 eV in MnSe to 2.30 eV in solid solutions of compositions x = 0.20–0.45. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 136–138, January–February, 2007.     

Recombination kinetics in nonlinear defective LiB3O5 crystals

A study of recombination kinetics in LiB₃O₅ (LBO) crystals by time-resolved luminescence and absorption spectroscopy is reported. An investigation of the kinetics of transient optical absorption (TOA) and luminescence under ns-scale electron-beam excitation performed within a broad temperature range of 77–500 K and a 1.2–5-eV spectral interval has established that the specific features in the recombination kinetics observed in LBO involve electronic, B²⁺, and hole, O⁻, trapping centers. The TOA and luminescence kinetics, as well as their temperature dependence, are interpreted by a model of competing hole centers. Relations connecting the kinetics parameters and the temperature dependence to the parameters of the main LBO point defects are presented. Fiz. Tverd. Tela (St. Petersburg) 40, 2008–2014 (November 1998)     

Thermooptical investigation of deep levels in doped Bi12SiO20 crystals

The temperature dependence of the impurity optical absorption of nominally pure Bi₁₂SiO₂₀ (BSO) crystals and BSO crystals doped with Ga, Cr, Mn, and Ag ions is investigated. A method is proposed for determining the thermal activation energy, and certain properties of deep levels are found. Fiz. Tverd. Tela (St. Petersburg) 40, 452–457 (March 1998)     

The effect of temperature on the photoluminescence ofp-CuGaSe2 single crystals

We studied the temperature dependences of spectral bands and of the outer quantum yield of the edge photoluminescence (PhL) of p-CuGaSe₂ single crystals obtained by the method of chemical transport reactions. We determined the activation energies of acceptor levels and showed that the temperature dependence of the intensity of PhL is determined by an acceptor level of 35 meV below the Debye temperature and of 150 meV above the Debye temperature. The spectra of the edge PhL at 300 and 80 K are determined mainly by band-band optical transitions. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 4, pp. 590–593, July–August, 1998.     

Absorption spectrum and excitons in thin films of the solid electrolyte RbCu4Cl3I2

We have investigated the absorption spectrum of thin films of the superionic conductor RbCu₄Cl₃I₂ synthesized on NaCl crystalline substrates. It is shown that the electron and exciton excitations in the energy interval 3–6 eV are associated with optical transitions in the CuHal sublattice, and the edge of the fundamental band is controlled by optical transitions in the Cu(II)Hal sublattice. It is found that the large band gap of this compound (E _g =3.86 eV) in comparison with those of CuCl and CuI is a result of the small number of Cu ions in the second coordination sphere. The temperature dependence of the spectral position and half-width of the low-temperature exciton band reveals features associated with the phase transitions γ→β (T _c1=170 K) and β→α (T _c2=220 K) and with disordering of the cation sublattice attendant to the transition to the superionic state. Fiz. Tverd. Tela (St. Petersburg) 40, 1022–1026 (June 1998)