Luminescence of CsBr:Eu films grown by liquid-phase epitaxy

By liquid-phase epitaxy from an aqueous alcoholic solution, we have obtained films of the well-known storage phospor CsBr:Eu, and we have studied their cathodoluminescence and photoluminescence (PL) spectra compared with the undoped CsBr films. We have established that the structure of the photoluminescence centers of the CsBr:Eu films when excited by laser radiation in the absorption band of the Eu²⁺ ions (λ = 337 nm) includes Eu²⁺-V_Cs isolated dipole centers and CsEuBr₃ aggregate centers, and also luminescence centers based on inclusions of hydroxyl group OH⁻ with the corresponding emission bands in the 440 nm, 520 nm, and 600 nm regions. We have studied the dependence of the spectra and the intensity of the photoluminescence for CsBr:Eu films on annealing temperature in air at 423–483 K, compared with analogous dependences for CsBr:Eu single crystals obtained from the melt. We have shown that annealing the films at T = 423–463 K leads to rapid formation of CsEuBr3 aggregate luminescence centers, while for T > 473 K thermal degradation of these centers occurs. We conclude that the observed differences between the photoluminescence spectra of CsBr:Eu films and CsBr:Eu single crystals may be due to additional doping of the films with OH⁻ ions. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 2, pp. 191–194, March–April, 2006.     

Low temperature photoconductivity of Pb1?xSnxTe?In? films at millimeter wavelengths

Photoconductivity of single crystal Pb_1−xSn_xTe〈In〉, (0.24≤x≤0.25), films at 4.2K in the wavelength region 4÷5 mm and magnetic fields up to 8 T was studied. Preparation technology of the films with high photoconductivity (P_FEP ≤ 10⁻¹² W×Hz^1/2) and photoresponsiveness (τ ≤ 10⁻⁶ s), as well as the measurements procedure are described in the paper. Also the mechanism of photoconductivity is discussed.     

Investigation of platinum oxide-titanium films by the method of X-ray photoelectron spectroscopy

Platinum oxide-titanium films that are produced by thermolysis of H₂PtCl₆ in the presence of NO ₃ ⁻ on a titanium surface are investigated by the method of x-ray photoelectron spectroscopy. It is shown that making nitrates a part of the composition leads to an increase in the content of oxidized forms of platinum and the appearance of titanium in the film. Belarusian State Technological University, 13a, Sverdlov St., Minsk, 220630, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 4, pp. 536–538, July–August, 1997.     

Crystal growth,electrical and photophysical properties of Tl<Subscript>2</Subscript>S layered single crystals

The Tl₂S compound was prepared in a single crystal form using a special local technique, and the obtained crystals were analysed by X-ray diffraction. For the resultant crystals, the electrical properties (electrical conductivity and Hall effect) and steady-state photoconductivity were elucidated in this work. The electrical measurements extend from 170 to 430 K, where it was found that σ _⊥ = 8.82 × 10⁻⁵ Sm⁻¹ when current flow direction makes right angle to the cleavage plane of the crystals. In the same range of temperatures, it was found that σ _‖ = 4.73 × 10⁻⁵ Sm⁻¹ when the current flow is parallel to the cleavage plane. In line with the investigated range of temperatures, the widths of the band gaps were calculated and discussed as also the results of the electrical conductivity and Hall effect measurements. In addition, the anisotropy of the electrical conductivity (σ _⊥/σ _‖) for the obtained crystals was also studied in this work. Finally the photosensitivity was calculated for different levels of illumination as a result of the photoconductivity measurements, which showed that the recombination process in Tl₂S single crystals is a monomolecular process.      

Characteristic features of the photoconductivity and spin conversion of electron-hole pairs in doped amorphous molecular semiconductors in the dye absorption region

The photoconductivity of doped poly-N-epoxypropylcarbazole films in the absorption region of a cationic polymethine dye is observed to increase when the BF ₄ ⁻ ion is replaced by Cl⁻ and I⁻. The effect of a magnetic field on the photoluminescence is investigated at room temperature. The photoconductivity is studied as a function of the electric field intensity and wavelength of light. The dependence of the photoconductivity on the nature of the anion can be explained by a change in the probability of intercombination conversion in ionic and electron-hole pairs. Fiz. Tverd. Tela (St. Petersburg) 41, 44–48 (January 1999)     

Vibrational spectra of CuAl x Ga1−x S2 solid solutions

Investigations of the IR reflection and Raman spectra in polarized light are carried out on single crystals of the ternary compounds CuAlS₂ and CuGaS₂ and solid solutions based on them grown by the method of chemical transport reactions. The frequencies of longitudinal and transverse phonons are determined, the IR intensities and damping factors of phonons (ε₀, ε_∞) are calculated, and their concentration dependences are constructed. It is established that optical vibrations in the solid solutions manifest a mixed behavior. Belarusian State University of Information Science and Radioelectronics 6 P. Brovka Str., Minsk, 220072, Belarus; e-mail: kafchim@gw.bsuir.unibel.by. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 6, pp. 800–803, November–December, 1999.     

Two-photon absorption by Nd3+ impurity ions in YAG and YLF crystals at 1.06 μm

A detailed theoretical analysis of the two-photon absorption spectra for YAG: Nd³⁺ and YLF: Nd³⁺ crystals was carried out in the 1.06 μm region with calculations of both the relative intensities between individual Stark sublevels of the⁴I_9/2→⁴G_7/2 transition of an Nd³⁺ ion and the integral two-photon absorption crosssections. The results of calculations agree well with experimental data. Reasons why the explanation of the experimental data given in [3] is very unsatisfactory and largely doubtful in itself are indicated. In conclusion, a relatively simple experiment is suggested that could give an unambiguous answer to some questions of the theoretical analysis performed. B. I. Stepanov Institute of Physics, Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 2, pp. 184–189, March–April, 1997.     

Preparation and properties of AgInS2 and AgInSe2 Single crystals and of the Quaternary alloys AgInSe2(1−x)S2x

Summary AgInS₂ and AgInSe₂ single crystals have been prepared by chemical transport with iodine and by the Bridgman method. Syntheses of the quaternary alloys AgInSe_2(1−x)S_2x have also been carried out. The splittings of the uppermost valence bands in orthorhombic AgInS₂ have been determined from the photoconductivity spectrum. The lattice parameters, the energy gap, the magnetic suceptibility and the melting point of all the materials are presented. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

Spectroscopic properties of Pr<Superscript>3 + </Superscript>-doped erbium oxalate crystals

Spectroscopic properties of praseodymium ions-doped erbium oxalate (Er₂(C₂O₄)₃ · nH₂O) crystals have been investigated. The crystals were grown by hydro silica gel method under suitable pH conditions and by single diffusion method. The well-grown crystals are bright and transparent. The dark green colour of these crystals changes with the variation of the concentrations of the dopant ions. The absorption spectra have been measured in the region 200–800 nm at room temperature. Judd–Ofelt intensity parameters for f–f transitions of the Pr³⁺ ions have been determined as Ω₂ = 166.7, Ω₄ = 1.103 and Ω₆ = 2.898. Analyses of the absorption spectra also show a possible energy transfer from the host material to the dopant.     

Physical properties of n-CdGeAs2 single crystals prepared by low-temperature crystallization

The first results obtained in studies of the temperature dependences of electrical conductivity and Hall constant of n-CdGeAs₂ single crystals prepared by low-temperature crystallization are reported. It has been established that the method developed permits growing single crystals with a free-electron concentration ⋍(1−2)×10¹⁸ cm⁻³ and a Hall mobility ⋍10000 cm²/(Vs) at T=300 K. It is shown that the temperature dependence of Hall mobility exhibits a behavior characteristic of electron scattering by lattice vibrations, whereas below 150 K a deviation from this law is observed to occur evidencing an increasing contribution of static lattice defects to scattering. The Hall mobility in the crystals prepared was found to reach ⋍36000 cm²/(Vs) at 77 K. Photosensitive heterojunctions based on n-CdGeAs₂ single crystals were prepared. The spectral response of the photosensitivity of these structures is analyzed. It is concluded that this method is promising for preparation of perfect CdGeAs₂ crystals. Fiz. Tverd. Tela (St. Petersburg) 41, 1190–1193 (July 1999)     

Remote detection of sulfur dioxide by means of a CO2 laser

The possibility of remote detection of SO₂ in the 9-μm region of the spectrum by means of a TEA CO₂ laser was theoretically and experimentally investigated with regard to the real state of the atmosphere and the contribution of background concentrations of H₂O, CO₂ and NH₃ to absorption. For sounding along short paths (2L=2 km), the method of detection of small concentrations of SO₂ (at the MPC level) with the use of the lines of the CO₂-molecule regular transitions (00^o1–02^o0 band) has been devised and experimentally tested. It is shown that in sounding along longer paths (2L=6 km), a noticeable increase in sensitivity can be achieved by the generation lines of the CO₂-molecule sequential 00^o2–02^o1 band. B. I. Stepanov Institute of Physics of the National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 4, pp. 508–515, July–August, 1998.     

Radiative and photoelectric properties of CuInS2 single crystals

The photoluminescence and photocurrent spectra of CuInS₂ single crystals grown by the Bridgman method are studied at temperatures of 80 and 300 K. The photosensitivity spectrum is observed in the shortwave photoluminescence band. From the watt-ampere characteristics of photoconductivity, a linear mechanism of recombination of minority charge carriers is established for an illumination level of up to 100 mW/cm² in the temperature range of 80–300K.     

Luminescence of silicon films on sapphire irradiated with high-energy particles

Using low-temperature (4.2–78 K) photoluminescence, we study the processes of defect formation in silicon films on sapphire irradiated with high-energy particles (electrons, γ-quanta of⁶⁰Co). It is established that carbon atoms, as a residual process impurity, participate in the formation of luminescence centers stable up to annealing temperatures of about 550 K. For carbon-containing centers we reveal a shift in the spectral lines relative to their position in spectra of single-crystal silicon. It is proposed that this spectral shift is associated with the presence of internal stresses of about 5·10⁸ N/m² in the silicon films. Institute of Solid-State Physics and Semiconductors, National Academy of Sciences of Belarus, 17, P. Brovka Str., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskefii, Vol. 66, No. 3, pp. 383–386, May–June, 1999.     

Optoacoustic gas analyzer based on a13C16O2 laser for multicomponent pollution of air

A computer-aided optoacoustic gas analyzer based on a continuous¹³C¹⁶C₂ laser for multicomponent pollution of atmospheric air is described. The analyzer has the ability to detect absorption of radiation by detected substances at the level of ∼1·10⁻⁹ cm⁻¹ at a time resolution of 30 sec. Results of an experiment on simultaneous detection of H₂O, CO₂, NO₂, NH₃, HNO₃, OCS, and C₂H₄ in the atmospheric air using 40 laser lines are presented. B. I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, 68, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 3, pp. 345–350, May–June, 1999.     

Photophysics ofβ-carotene and related compounds (review)

A review of data on the photophysics of carotenoids is presented. Results of investigations of spectroscopic, temporal, and energy parameters of excited S₁ and S₂ singlet states of β-carotene and related compounds are critically examined. These states give rise to extremely high probabilities (10¹¹–10¹³ sec⁻¹) of radiationless deactivation of the electronic excitation energy in carotenoids. Results of investigations of photophysical properties of triplet states of carotenoids are considered mainly from the standpoint of quenching of singlet oxygen and triplet states of organic molecules by carotenoids. Institute of Molecular and Atomic Physics, Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 5–19, January–February, 1997.     

On new two-dimensional structures produced on the Si (111) and Si (100) surface upon molecular-beam epitaxy of cobalt and silicon

Highly perfect epitaxial heterostructure CoSi₂ films have been grown on the surface of Si (111) and Si (100) single crystals by the method of molecular-beam epitaxy. The optimal regimes of the film growth with different thicknesses have been determined. It has been shown that short-term annealing of epitaxial films at T = 900–950 K leads to the formation of new CoSi₂/Si(111)-2 × 2 and CoSi₂/Si(100)−2 × 4 superstructures.     

Charge transport properties of undoped congruent lithium niobate crystals

Time-resolved light-induced birefringence measurements based on a phase compensation technique are used to determine the charge transport properties of congruent, nominally-undoped lithium niobate crystals (LiNbO₃). Some of the crystals are conventionally oxidized. The steady-state space-charge field E _pv, the bulk photovoltaic coefficient β, and the photoconductivity σ _ph are determined in the intensity range (30–30 000) W/cm². The photovoltaic coefficient β increases by one order of magnitude over this intensity range, the space-charge field E _pv even by two orders of magnitude. We discuss the results in the context of the known one- and two-center charge transport models for LiNbO₃. The experimental findings presented here are of relevance for the long-standing problem of optical damage in such crystals, which inhibits their use in high-intensity applications like nonlinear optics.     

Investigation of the optical properties of AgGaTe2 films obtained by laser deposition

We obtain thin films of AgGaTe₂ by laser vaporization of starting crystals. The compositions of the starting crystals and of the films obtained are determined by x-ray spectral analysis, with their structure and the parameters of the crystal lattice being determined by the x-ray method. The energies of interband transitions and crystalline (Δ _cr ) and spin-orbit (Δ _so ) splitting are calculated from transmission spectra in the region of the main absorption band. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 6, pp. 793–796, November–December, 1997.     

Effect of isoelectronic impurities K<Superscript>+</Superscript> and I<Superscript>−</Superscript> on luminescence of CsBr:Eu<Superscript>2+</Superscript> crystals

We have investigated the photoluminescence (PL) and photostimulated luminescence (PSL) spectra at 300 K to study the effect of isoelectronic impurities K⁺ and I⁻ on the formation and energy structure of Eu²⁺-V_Cs isolated dipole centers and aggregate centers in the form of single crystals of CsEuBr₃ in CsBr:Eu²⁺ single crystals. We have shown that K⁺ and I⁻ impurities in a concentration of 5 mol% do not have a substantial effect on the energy spectrum of isolated dipole centers in CsBr:Eu²⁺ single crystals and the processes for the formation of such centers during growth of CsBr:Eu single crystals from the melt by the Bridgman method. We have established that in Cs_0.95K^0.05Br:Eu²⁺, more favorable conditions are realized for the formation of aggregate centers than in CsBr:Eu²⁺ and CsBr^0.95K^0.05Br:Eu²⁺ single crystals. So in order to improve the storage properties of phosphors based on CsBr:Eu²⁺, in particular for increasing the efficiency of PSL excitation, it is expedient to dope them with K⁺ impurity in a concentration up to 5 mol%. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 5, pp. 627–630, September–October, 2007.     

Induced impurity photoconductivity in crystals of Si-and Ge-sillenites

The spectral distribution of the uv-induced photoconductivity intensity and relaxation in Bi₁₂SiO₂₀ and Bi₁₂GeO₂₀ crystals both undoped and doped with Al, Ga, Cr, Cu, Mn, and V is investigated in the optical range 0.5–3.5 eV in the temperature ranges 85–95 K and 285–295 K. It is shown that in the short-wavelength region 2.2–3.5 eV it is controlled by multicenter recombination in which both “fast” and “slow” recombination participate. Fiz. Tverd. Tela (St. Petersburg) 40, 1027–1029 (June 1998)