L.D. Bogomolova

The electron paramagnetic resonance and optical spectra of copper and vanadium in phosphate glasses

Abstract In the present work the results of the systematic study of the EPR spectra of Cu2+ and V4+ ions in binary phosphate glasses are discussed. A comparison of the behaviour of the EPR spectra of two kinds of ions in the same glassy matrix allows one to determine more accurately the location of each kind of ions in this matrix. This paper deals mainly with the phosphate glasses ROP2O5 containing divalent modificators (R = Ca, Sr, Ba, Mg, Zn, Pb). The optical spectra were recorded on a SP-8 spectrophotometer in the range 300–1000 nm. The EPR spectra were recorded at room temperature on the EPR-3 spectrometer made in the USSR and operating in the X-band.

Electron paramagnetic resonance of Cu2+ and V4+ ions in borate glasses

Abstract The EPR spectra of Cu 2+ and V 4+ ions have been studied in binary ROB 2 O 3 glasses (where R = Ba, Sr, Pb and Zn) and in ternary PbOZnOB 2 O 3 glasses. The main results of an EPR study of alkali-borate glasses are briefly reviewed. Three distinct EPR spectra of Cu 2+ ions in barium-borate glasses were observed. The superposition of two EPR spectra of a Cu 2+ ion in glasses containing from 5 to 15 mol.% BaO is attributed to a stable liquid immiscibility in these glasses. The structural similarity of barium- and strontium-borate glasses containing 30–40 mol.% RO is established. It is concluded that non-bridging oxygens appear in these glasses for higher concentrations of a modifier than in alkali-borate glasses. The data for Cu 2+ ions in PbOB 2 O 3 glasses containing from 20 to 40 mol.% PbO suggest a modifying role for Pb 2+ at such PbO concentrations. Very marked differences between the spectral parameters of low- and high-lead borate glasses are found for a V 4+ ion. The superposition of two distinct EPR spectra of V 4+ ions in binary ZnOB 2 O 3 glasses is observed and is attributed to the two-phase structure of these glasses. The structural roles of Pb 2+ and Zn 2+ in ternary PbOZnOB 2 O 3 glasses are discussed. The tendency of the Cu 2+ ion to be localized far from lead and zinc ions playing the roles of network formers is established. The high sensitivity of the V 4+ EPR spectra to the main structural units is suggested.

The study of interactions between iron and vanadium ions in semiconducting barium-vanadate glasses doped with Fe2O3

Semiconducting barium-vanadate glasses doped with Fe2O3 ranging from 0.1 to 10 wt% were studied. We made attempts to understand features of an incorporation of the impurity ions into the host matrix. EPR, magnetic susceptibility, dc-conductivity and the Mossbauer effect were investigated. It was established that iron entered into the host as Fe3+·Fe3+ and V4+ ions formed associates coupled by dipole-dipole interactions for low Fe2O3 contents in the glass. The V4+−Fe3+ and Fe3+−Fe3+ pairs co-existed for all glasses. The contribution of Fe3+−Fe3+ interactions increased with increasing Fe2O3 content. The deviation from paramagnetic behaviour was observed for glasses with 8–9 wt% Fe2O3. It was attributed to presence of fine crystalline magnetic particles. The iron impurity induces no considerable changes in the dc-conductivity of the glass. The concentration dependence of dc-conductivity exhibits a minimum of about 5–6 wt% Fe2O3.

EPR of some oxide glasses implanted with Mn+ and Cu+ ions

Abstract Electron paramagnetic resonance (EPR) spectra of Mn2+ and Cu2+ ions in some Mn+- and Cu+-implanted multicomponent silicate (20Na2O10B2O370SiO2, mol%) and phosphate (36P2O544Na2O20Al2O3 and 65P2O510B2O310Al2O315MgO, mol%) glasses are presented. About 10% of the implanted copper is present as Cu2+ ions surrounded by six ligands which form a tetragonally elongated octahedron. The concentration of Mn2+ ions in the implanted layers of some glasses is comparable with that of implanted manganese ions. The EPR spectra of Mn+-implanted high-phosphate glass indicate that Mn2+ ions can exist in the implantation layers in local environments similar to those present in bulk glasses with appropriate composition. In addition, Mn2+ ions are present in the implantation layers as paramagnetic ions coupled by spin-spin interactions or antiferromagnetic MnO crystals.

EPR of transition metals in fluoroaluminate glasses

Abstract The results of EPR study of fluoroaluminate glasses (FAG) in the AlF3-YF3-RF2 system (where R = Mg, Ca, Sr, Ba) doped with small amounts of transition metals (Ti, V, Mn, Fe, Co, Cu) are presented. The EPR spectrum of Ti3+ ions in FAG is similar to that reported for many glasses and can be described by g1 = 1.96 and g2 = 1.91 at 77 K. The vanadium-containing FAG exhibit EPR spectrum only when V is introduced as vanadium oxides; this spectrum belongs to VO2+ ions and can be described by an axial spin-Hamiltonian with parameters (determined by fitting the experimental and simulated spectra): g∥ = 1.949; g⊥ = 1.980; A∥ = 163 × 10−4 cm−1; A⊥ = 63 × 10−4 cm−1. An X-band spectrum of Mn2+ ions consists of a well-resolved sextet near g = 2.0 and weak background and g ≅ 4.3 resonances. The hyperfine splitting of the g ≅ 2.0 resonance measured at the Q-band is A = 98.5±0.5 Oe. Concentration dependence of the EPR spectrum permits one to assume a more uniform distribution of Mn2+ ions in FAG than in HMFG where these ions are believed to be clustered. Iron is present in FAG predominately as Fe2+ ions. A small portion of Fe3+ ions gives EPR spectrum which is similar to that in oxide glasses but very different from the spectrum observed for Fe3+ in HMFG. By contrast with fluoroberyllate glasses for which EPR signals of Co2+ have been observed at 77 K the broad single line centered near g ∼ 4.3 is observed for Co2+ in FAG only at 4.2 K. The EPR spectra of FAG containing copper are superpositions of the spectra of isolated Cu2+ ions and the almost isotropic line belonging presumably to crystalline occlusions which undergo cooperative Jahn-Teller effect. The spectrum of Cu2+ ions dissolved in FAG exhibits superhyperfine structure with a splitting of about 50 Oe from the interaction of unpaired electrons of Cu2+ ions with 19F nuclei.

EPR of Cu2+ ions in heavy metal fluoride glasses

Abstract EPR spectra of Mn 2+ ions in two systems of heavy metal fluoride glasses are investigated. The compositions (in mol.%) of the base glasses are 60 XF 4 -5LaF 3 -20 BaF 2 -15 NaF (where X is Zr or Hf). The glasses were doped with MnF 2 at concentrations from 0.05 to 0.3 wt%. EPR observations were made at the X-band and Q-band frequencies. A hyperfine sextet with a splitting of about 100 Oe is observed. At the X-band the hyperfine spectrum is superimposed on a very broad background line. A weak reasonance absorption with g ≅ 4.3 and hyperfine splitting of about 100 Oe is found. The background line and g ≅ 4.3 spectrum disappear at the Q-band. The peak-to-peak linewidths of hyperfine components of the g ≅ 2.0 line depend strongly on Mn concentration. Forbidden Δm = ∓ 1 transition and superhyperfine structure arising from 19 F ligands were not detected. It is concluded that Mn 2+ sites are characterized by broad distribution of crystal-field parameters. This is attributed to the fact that Mn 2+ impurities can be incorporated in positions with a broad distribution of MnF distances which is expected for the glasses with a broad distribution of the distances between host atoms. A non-random distribution of Mn 2+ ions which tend to be clustered in some regions of the glass network is assumed.

Some features of EPR and optical spectra of vanadium in aluminophosphate glasses

Abstract The EPR and optical spectra of vanadium in glasses of ternary Al2O3P2O5SiO2 and Al2O3P2O5B2O3 systems have been measured. The results were compared with earlier data for vanadium in binary phosphate, aluminophosphate and silicaphosphate glasses and with results of de-Biasi for V4+ in crystalline powder α-crystobalite AlPO4. The superpositions of two hyperfine spectra (ASB-I and ASB-II) were found for many glasses of ternary systems. Both spectra can be attributed to VO2+ ions. The intensity ratio of the ASB-II spectrum to ASB-I depends on glass composition but is great (> 7) for all the glasses. Only the ASB-II spectrum was observed in glasses with low concentration of Al2O3. The spectral parameters of ASB-II spectrum are g| = 1.916–1.921; g⊥ 1.980–1.988; A| = (188−190) × 10−4 cm−1 and A⊥ = (74–77) × 10−4 cm−1. Three intense bands at 370, 455 and 700 ans 720 nm observed in these glasses can be attributed to V3+ ions. The excellent agreement of the parameters of the EPR spectrum of V4+ ions in crystalline α-crystobalite AIPO4 and ASB-II spectra in the glasses under study suggest the identical electron structure of the paramagnetic species. This species is believed to be characterized by optical bands at 680 and 790 nm which have been observed by de Biasi. The orbital mixing coefficients indicate strong tetragonal distortion of vanadyl complexes responsible for the ASB-II spectrum. It is assumed that VO2+ ions responsible for this spectrum act as modifiers fitting into the relatively small holes of the three-dimensional networks of phosphate glasses containing no cations of large radii. The microscopic basicity of oxygens in such holes must be about 0.48.

EPR of silica and fluoride glasses implanted with titanium and zirconium

Abstract Silica substrates were implanted with Ti+ ions to nominal doses (D) ranging from 5×1016 to 6×1017 ions/cm2 at an energy of E=160 keV. The lines of electron paramagnetic resonance (EPR) with g=1.938 to 1.944 are attributed to Ti3+ with ground state |xy〉 located in tetragonally compressed oxygen octahedron. Computed spectra of some samples implanted with Ti, besides the line at g=1.94, contain two isotropic lines with (g=1.968 and g=1.972) which are assigned to Ti3+ ions entering clusters or compounds of titanium with silicon or oxygen. The greater fraction of implanted Ti exists in non-paramagnetic states. In silica glass implanted with Zr+ (E=195 keV, D=5×1016 and 1017 ions/cm2) Zr3+ ions in the amount of 0.5–1% of implanted Zr are in distorted octahedral environment producing an asymmetric line with g∼1.916 and width ∼14 mT. For fluoroaluminate glass (FAG) implanted with Ti+ (E=150 keV, D=2×1016,5×1016 and 10 17 cm −2 ) EPR line at g=1.944 and optical absorption band at ∼475 nm similar to those observed earlier for FAG doped with TiO2 were assigned to Ti3+ ions in tetragonally compressed octahedron. In the EPR spectra of FAG coimplanted with Ti+ (E=150 keV) and F+ (E=90 keV) the triplet centered at g=1.9375 with ratio of intensities of components equal to 1:2:1 and the separation between adjacent components equal to 1.1 mT was observed and attributed to TiF+2 molecular ions. The integrated intensity of this triplet in relation to that of the g∼1.94 single line varies from 0.6% to 2% depending on F+ dose. The decrease in the content of Ti3+ ions with increasing implantation dose is interpreted in terms of chemical sputtering of Ti–F molecules. The g-values of Zr3+ ions incorporated into fluorozirconate glass (FZG) after the implantation of Zr+ ions differ from those obtained earlier for F-center near Zr4+ in X- or γ-ray irradiated FZG. We conclude that some part of the implanted zirconium is incorporated into FZG as Zr3+ in distorted octahedral environment. Structural defects produced in silica and fluoride glasses by Ti+- and Zr+-ion implantation are not discussed.

On the formation of radiation-induced defects in fluoroaluminate glasses

The spectra of electron paramagnetic resonance (EPR) of fluoroaluminate glass (FAG-36) based on mineral usovite Ba2CaMgAlF14 were studied. The paramagnetic centers responsible for EPR signals were induced by ion bombardment of the substrates prepared from this glass. The N+, O+, Ar+ and Pb + ions with energy E = 150 keV were used. The integrated dose D was 2 × 1016 ions/cm2. It is shown by means of isochronal anneal experiments and computer simulation of the EPR spectra that they contain four components: broad Gaussian line (GL) with g = 2.016 and σ oscillating in the range 30–40; two anisotropic spectra with gz = 2.016, gy = 2.009; gx = 2.001 (FA1) and gz = 2.045; gy = 2.010; gx = 1.98 (FA2) as well as narrow isotropic line of Lorentzian shape with g = 2.0025 and ΔH = 0.6 mT. The comparison of obtained results with literature data for γ-irradiated fluoride glasses and ion-implanted oxide glasses of different compositions permitted to conclude that GL is due to hole defects typical of fluoride glasses and localized on several anions (fluorines and oxygen(s)); anisotropic FA1- and FA2-spectra are attributed to molecular 02−-ions, and narrow isotropic signal is supposedly assigned to big molecular ions (O2O−, 04− , CO+, CO−) located in voids of damaged implantation layer.

EPR of radiation-induced defects in fluoroaluminate glasses

Abstract The electron paramagnetic resonance spectra of multicomponent fluoride glasses in the system AlF3YF3ΣRF2 (R = Ba, Ca, Sr, Mg) have been measured after γ-ray irradiation at 77 K. The samples of nominal compositions Ba2EMgAl2F14 (E = Sr, Ca, Pb) and BaYRMgAl2F15 (R = Ba, Sr, Ca, Zn, Cd, Pb) were investigated in the same manner for comparison purposes. The hole center, F2−, has been identified in these materials. An electron center with g∥ = 1.995 ± 0.005 and g# = 1.93 ± 0.01 has been attributed to a Y2+ ion which can be considered as a Y3+ ion that has trapped an electron on its d-orbital. This center annealed out between 110 and 120 K. The symmetric single line with g = 2.015 ± 0.002 and linewidths varing from 4.5 to 7.5 mT for different samples has been observed in a wide range of temperatures (from 77 to 520 K). It is assumed that this line is the superposition of two hole signals: one of them is a hole trapped on several fluorine ions and the other is a hole trapped on an oxygen impurity. The high oxygen content, which is confirmed by X-ray photoelectron spectroscopy measurements, leads to a broadening of the line attributed to oxygen impurity.