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. L’vov State University, 50, Dragomanov St., L'vov, 290005, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 1, pp. 143–145, January–February, 1998.     

Luminescence of Thin Films of Lead and Bismuth Tungstates

The luminescence spectra of thin films of PbWO₄ and Bi₂WO₆ were investigated. It is shown that these spectra are similar and that they consist of three individual bands in the blue (2.80 eV PbWO₄ and 2.93 eV Bi₂WO₆), green (2.35 eV PbWO₄ and Bi₂WO₆), and red (1.75 eV PbWO₄ and 1.90 eV Bi₂WO₆) spectral regions. The differences in the nature of the absorption centers of excitation energy are established. The distinguishing features displayed by the temperature dependences of the individual emission bands in the PbWO₄ films are explained by energy migration between emission centers via transfer of free carriers through the conduction and valence bands.     

Dispersion of light and EDGE absorption of thin Y2O3 films

We measured the dispersion of light in thin Y₂O₃ films in the visible and near UV regions of the spectrum. The spectrum of edge absorption is investigated. We found the parameters of a single-oscillator approximation and determined the dispersion energy and the ionicity of bonding. I. Franko L’vov State University, 50, Dragomanov St., L’vov, 290005, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 5, pp. 651–654, September–October, 1997.     

Thermostimulated Luminescence of PbWO4, Bi2WO6, and Y2WO6 Ceramics

Thermostimulated luminescence (TSL) of PbWO₄, Bi₂WO₆, and Y₂WO₆ ceramics on x-ray excitation is investigated. The spectral luminosity of the thermostimulated luminescence is analyzed. The thermal activation energies conforming to the corresponding thermostimulated luminescence peaks are determined. It is established that on emptying trapping centers radiative recombination occurs at the intrinsic-luminescence centers associated with tungsten-oxygen complexes WO₄ ^2–.     

Optical and EPR spectroscopy of manganese ions in Sr3Ga2Ge4O14 crystals

Results of investigations of the spectroscopic properties of manganese-activated single crystals of Sr₃Ga₂Ge₄O₁₄ by the methods of optical and EPR spectroscopy are reported. It is shown that magnagese activator ions form substitutional centers Mn³⁺ and Mn²⁺ in 1a-octahedral positions of the Sr₃Ga₂Ge₄O₁₄ lattice. Changes in the opticla properties of Sr₃Ga₂Ge₄O₁₄: Mn after vacuum thermal annealing are attributed to charge transfer of some of the manganese ions (Mn³⁺→Mn²⁺). The relationship between the spectroscopical properties of Mn²⁺ ions and the crystallochemical structure of the system are discussed. I. Franko L’vov State University, 50, Dragomanov St., L’vov, 290005, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 6, pp. 779–783, November–December, 1997.     

The absorption spectrum of radiation-colored SrCl2-Ce crystals

We investigate the spectra of the x-ray radiation-induced absorption of SrCl₂−Ce crystals over the spectral range 345–830 nm and their temperature transformations in the interval from 77 to 450 K. We found that radiative color centers are characterized by a complex spectrum of induced absorption that contains wide bands of photochromic PC (750, 519, 378 nm) and PC⁺ (620, 446, 340 nm) centers and quasi-linear bands of Ce²⁺ centers. The most significant thermal transformations of radiative color centers occur in the vicinity of the thermostimulated luminescence peak of 394 K, at which the holes of the PC⁺ centers recombine with the electrons of the Ce²⁺ centers. Ivan Franko L’vov State University, 8, Kirilla i Mefodiya St., L’vov 290005, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 4, pp. 545–547, July–August, 1997.     

ESR spectroscopy of La2Ga5SiO14:Cr single crystals

The ESR spectrum of La₃Ga₅SiO₁₄ single crystals activated by chromium ions is investigated. It is shown that chromium ions are incorporated into the La₃Ga₅SiO₁₄ crystal lattice in the trivalent state at laoctahedric positions. Orientations of the principal magnetic axes are determined, and parameters of the spin Hamiltonian are estimated. The effect of disorder of the crystal structure of the matrix on line widths and shapes of the ESR spectrum of impurity Cr³⁺ ions is discussed. I. Franko L’vov State University, 50, Dragomilov St., L’vov, 290005, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 6, pp. 942–946, November–December, 1998.     

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. L’vov State University, 50, Dragomanov St., L’vov, 290005, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 6, pp. 776–778, November–December, 1997.     

X‐Ray Luminescence of Thin Oxide Films Containing Lead and Bismuth

We obtained thin films of the Bi₄Ge₃O₁₂, Bi₄Si₂O₁₂, PbWO₄, and Bi₂WO₆ scintillators and investigated their luminescence properties on xray excitation. We measured the xray luminescence spectra and established the linear character for the dependence of the luminescence intensity on the power of the dose of xray irradiation within the limits of up to 3·10^–3 A/kg. We investigated the radiation stability of the films obtained. The possibility of their application for detecting ionizing radiation is investigated. The films based on Bi₄Ge₃O₁₂ with an admixture of the Ge and Si or Mn activator of up to 1.5 mol.% are most suitable.     

Preparation, structures and photoluminescent enhancement effect of PbWO4–TiO2 composite nanofilms

A novel route for preparing PbWO₄–TiO₂ nanofilms on a glass substrate is firstly proposed. The collodion is used as a dispersant and film-forming agent. The nanofilms are characterized through SEM, XRD, TG/DTA, PL and IR, respectively. The results of XRD indicate PbWO₄ particles with tetragonal scheelite structure and TiO₂ particles with Anatase phase, and SEM shows they are well dispersed in the substrate. Compared with nanoparticles, when TiO₂ nanoparticles are added in 5% ratio, the PL intensities at 395 nm of PbWO₄ nanofilms are enhanced obviously. IR spectrum reveals a large absorption band between 750 and 870 cm⁻¹, which is the W–O stretching vibration in WO₄ tetrahedron.     

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. I. Franko L’vov State University, 50, Dragomanov St., L’vov, 290005, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 4, pp. 528–531, July–August, 1998.     

Optical properties of the proton conductor (NH2(CH3)2)2CoCl4

Based on the data from optical-spectral studies of (NH₂(CH₃)₂)₂CoCl₄ crystals, the existence of high-temperature phase transitions at 419, 380, 352, and 313 K is confirmed. It was shown that with the exception of the first transition, they are related to a considerable extent to rearrangement of the network of hydrogen bonds and are not accompanied by, considerable deformation of the lattice. In this connection the character of the electron-phonon interaction remains unchanged in the entire temperature range of the measurements. The (NH₂(CH₃)₂)₂CoCl₄ structure at room temperature is close to that of the ordered low-temperature phases of such isomorphous crystals as β-K₂SO₄. I. Franko State University, L’vov, Ukraine, 8, Kirill and Mefodii St., UA-290005, L’vov. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 3, pp. 412–418, May–June, 1998.     

Luminescence of Thin Bi2W2O9 Films

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.     

Towards a thin films electrochromic device using NASICON electrolyte

The optimisation of the morphology of WO₃ thin films allowed a more efficient electrochromic colouring using Na⁺ ions than H⁺ ones. Therefore, sodium superionic conductor (Na₃Zr₂Si₂PO₁₂, NASICON) films may be used as electrolyte in inorganic electrochromic devices. In this paper, the structure, chemical composition, morphology and electrochromic properties of WO₃, ZnO:Al and Na₃Zr₂Si₂PO₁₂ thin films were studied to develop a novel type of electrochromic device. WO₃, ZnO:Al and Na₃Zr₂Si₂PO₁₂ thin films were deposited using reactive magnetron sputtering of tungsten, zinc and aluminium and Zr–Si and Na₃PO₄ targets, respectively. For transparent conductive oxide coatings, a correlation was established between the deposition parametres and the film’s structure, transmittance and electrical resistivity. Classical sputtering methods were not suitable for the deposition of NASICON films on large surface with homogenous composition. On the other hand, the use of high-frequency pulsed direct current generators allowed the deposition of amorphous films that crystallised after thermal annealing upon 700 °C in the Na₃Zr₂Si₂PO₁₂ structure. Amorphous films exhibited ionic conductivity close to 2 × 10⁻³ S cm⁻¹. Finally, preliminary results related to the electrochromic performance of NASICON, WO₃ and indium tin oxide devices were given. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, France, Sept. 9–15, 2007.     

Electrochromic properties of tungsten oxides synthesized from aqueous solutions

Tungsten oxides are known to exhibit interesting electrochemical properties. Ion insertion (Li⁺, H⁺) within the oxide network is highly reversible. It leads to a blue coloration and WO₃ thin films can be used as electrochromic layers in display devices or smart windows. Tungsten oxide thin films can be conveniently deposited from aqueous solutions of tungstic acid. However polytungstic acids are not stable and tend to precipitate into hydrated tungsten oxide WO₃⋅2H₂O. The condensation of polytungstic species can be chemically controlled by adding foreign ions in the solution. Precipitation is no more observed in the presence of H₂O₂. Peroxopolytungstic acids are formed in which chelating [O₂]²⁻ ligands prevent the formation of an oxide network. Such solutions are specially convenient for the deposition of optically transparent thin films. Mixed oxides WO₃-MoO₃ are obtained when condensation is performed in the presence of Mo⁶⁺ cations. This paper shows how the condensation of tungstic acid can be chemically controlled and describes the electrochemical properties of the films deposited from such solutions. Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, Sept. 13–19, 1997     

Luminescence of mercurylike impurities in single-crystal CdWO4 compounds

The processes of crystallization by the method of liquid epitaxy are studied for the first time for single-crystal films of CdWO₄ doped with the mercurylike ions Bi³⁺ and Pb²⁺, which can be used as thin-film components of combined scintillators for monitoring α- and β-activities. It is shown that in comparison with their solidcrystal analogs, the special features of these films consist in a longwave shift of the integral luminescence spectrum that is caused by high concentrations of the radiating complexes (V_Cd-WO₆) with hv_max=2.05–2.15 eV and the “distorted” complexes (WO₆)^* in them. It is found that in the case of luminescence of single-crystal films CdWO₄:Pb, radiation of mercurylike centers (PbO₆) prevails with hv_max=2.87 eV, while in luminescence of CdWO4, radiation of centers (BiO₆) with hv_max=2.16 eV and of complexes (V_Cd-WO₆). Institute of Applied Physics, Iv. Franko Lvov State University, 49, General Chuprynka St., Lvov, 290044, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 2, pp. 211–215, March–April, 1998.     

Effect of the excimer laser irradiation on sol–gel derived tungsten–titanium dioxide thin films

A novel technique based on the excimer laser induced crystallization and modification of TiO₂ thin films is being reported. W⁺⁶ ions loaded TiO₂ (WTO) precursor films were prepared by a modified sol–gel method and spin-coated onto microscopic glass slides. Pulsed KrF (248 nm, 13 ns) excimer laser was used to irradiate the WTO amorphous films at various laser parameters. Mesoporous and nanostructured films consisting of anatase and rutile were obtained after laser irradiation at room temperature. The effect of varying W⁺⁶ ions concentrations on structural and optical properties the WTO films was analyzed by X-ray diffraction, field-emission scanning electron microscope, UV-Vis spectrophotometer and transmission electron microscope before and after laser treatment. Films irradiated for 10 pulses at 65–75 mJ/cm² laser fluence, exhibited anatase whereas higher parameters promoted the formation of rutile. XPS results revealed WO₃ along with minor proportion of WO₂ compounds after laser irradiation. Photo-absorbance of the WTO films was increased with increase in W⁺⁶ ions concentration in the film. TEM results exhibited a crystallite size of 15 nm which was confirmed from SEM results as well.     

Thermally and photostimulated recombination processes in PbWO4 crystals at low temperatures

We have studied thermally and photostimulated recombination processes in PbWO₄ crystals in the temperature interval 90–295 K. We have shown that after x-ray excitation of the crystal at 90 K, the thermally stimulated luminescence curve shows a relatively intense peak at 110 K and weak peaks at about 173, 191, and 232 K. Exposure of the PbWO₄ crystal to IR radiation after excitation by x-ray photons leads to the appearance of photostimulated flash luminescence, a significant decrease in the intensity of the 110 K peak, and a shift of that peak to the 116 K region. But long-wavelength illumination has less of an effect on the intensity and position of the higher temperature peaks. It is assumed that F⁻ centers are formed in the PbWO₄ crystal at 90 K during x-ray exposure. The thermal light sum released by IR illumination in the temperature region 90–150 K has a maximum at ≈108 K. The nature of this maximum is connected with the complex centers [Pb³⁺ + (WO_3-F⁻)]. Optical and thermal degradation of these centers leads to the appearance of emission in the green region of the localized exciton spectrum.     

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. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 5, pp. 688–691, September–October, 2007.     

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. Translated from Zhurnal Prikladnoi Spektroskopii, Vol 67, No. 2, pp. 273–275, March–April, 2000.