A. M. Mironov

Irradiation-induced and postirradiation processes in fluoroaluminate glasses

We have measured the EPR and induced optical absorption spectra of several fluoroaluminate glasses prepared under different redox conditions and containing NH4HF2, EuF3, or Eu2O3 additions. Analysis of spectra taken after gamma irradiation to various doses and isothermal bleaching kinetics of individual absorption bands indicates that the color centers responsible for induced absorption in the UV spectral region are hole traps related to either oxygen (45000 and 42000 cm−1) or fluorine (37500 cm−1). In the visible range, we have revealed three absorption bands. We assume that the 17400 cm−1 absorption is due to an electron trap involving Y3+. Our data suggest some evidence that paramagnetic hole centers and electronic color centers may be formed in the same events.

Specific features of the induced absorption spectra of fluoroaluminate glasses doped with samarium ions

The induced optical absorption spectra of γ-irradiated fluoroaluminate glasses doped with Eu3+ and Sm3+ ions are investigated. It is shown that Sm3+ ions in fluoroaluminate glasses are protector ions contributing to the suppression of induced absorption in the optical absorption spectra of the studied glasses. It is revealed that the induced optical absorption spectra of the glass samples heat treated at T = 583°C contain two absorption bands with maxima at 300 and 480 nm, which correspond to radiation-reduced (Sm3+)–. The concentration of color centers produced by γ-radiation in fluoroaluminate glasses is estimated. It is demonstrated that prolonged heat treatment of the glass at T = 638 K brings about the decay of (Sm3+)– centers followed by the destruction of the samples.

Effect of secondary heat treatment on the spectroscopic properties of Na2O-Nb2O5-P2O5 glasses

We have studied the optical absorption and luminescence spectra of 45Na2O · xNb2O5 · (55 − x)P2O5 glasses containing 5, 10, 20, 25, 30, and 35 mol % Nb2O5. The results indicate that the absorption band around 26000 cm−1, responsible for the yellow color of the glasses, is due to the [Nb(5+)--O−] center and disappears upon secondary heat treatment. Heat treatment of europium-doped glasses increases the concentration of Eu3+ centers in an asymmetric environment, which is accompanied by an increase in luminescence efficiency. The reason for this is that the Eu3+ ions are located outside the niobate subsystem of the glass matrix. The europium in the glasses studied acts as a protector ion.

Local environment of Eu3+ and Tb3+ ions in fluorophosphate glasses of the Ba(PO3)2-MgCaSrBaAl2F14 system

The induced optical absorption and EPR absorption spectra of fluorophosphate glasses of the compositions 40Ba(PO3)2 · 60MgCaSrBaAl2F14 and 5Ba(PO3)2 · 95MgCaSrBaAl2F14 doped with Tb3+ and Eu3+ ions are investigated within the model of the effective capture volume of free carriers. The concentration dependences of the relative number of radiation centers on the dopant concentration in fluorophosphate glasses are analyzed. It is established that the character of the distribution of dopant ions in glasses depends on the dopant concentration and the structure of the glass. The critical concentrations at which the oxygen local environment of Eu3+ or Tb3+ ions in the structure of fluorophosphate glasses transforms into a mixed local environment are determined for glasses of the compositions under investigation.

Effect of thermal treatment on spectroscopic properties of europium doped niobate phosphate glasses

Glasses of the following composition 45Na2O•(55 - x)P2O5•xNb2O5 and 50Na2O•(50 - x)P2O5•xNb2O5 are studied. It is found that under the influence of γ-radiation the glass color changes. Optical absorption spectra, photoluminescence spectra, Rayleigh and Mandelshtam - Brillouin scattering (RMBS) spectra are investigated in dependence of glass composition, europium concentration, thermal treatment duration and radiation dose. Effect of secondary thermal treatment is studied on the base of 45Na2O•25P2O5•30Nb2O5 doped with 1 mol.% Eu2O3. It is found that intensity of photoluminescence gives rise and decay time as well under thermal treatment at the temperature exceeding transition temperature by 50 degrees. RMBS spectra of glasses after thermal treatment demonstrate decrease of scattering intensity while Eu2O3 being doped. Effects obtained are accounted for europium ion local symmetry changes.

Radiation-induced color centers in γ-irradiated glasses in the Na2O-Nb2O5-P2O5 system

The specific features of the induced optical absorption spectra of glasses in the 45Na2O · xNb2O5 · (55 − x)P2O5 system with Nb2O5 contents x = 5, 10, 20, 25, 30, and 35 mol % are investigated as functions of the irradiation dose and the heat treatment time. The spectra are decomposed into Gaussian components with the use of computer processing. It is revealed that the glass composition and the irradiation dose affect the number, type, and parameters of the bands associated with the PO42− hole-type centers, electron-type color centers of the phosphate matrix, [Nb(5+)−] one-electron centers, and [Nb(5+)−-O-Nb(5+)−] two-electron centers. The inference is made that heat treatment at temperatures close to the glass transition point Tg leads to the formation of groupings with a structure similar to structural motifs of NaNbO3 crystals. It is demonstrated that these groupings are responsible for the induced optical absorption in the near-IR spectral range.

Structural microinhomogeneity of fluorophosphate glasses with small additions of europium

The structural microinhomogeneity of EuF3 doped fluorophosphate glasses is studied to elucidate the influence of the Eu3+ ion environment on Rayleigh scattering. The measurements of Rayleigh and Mandelstam-Brillouin scattering, small-angle x-ray scattering, y-ray induced optical absorption, and fluorescence are used. It is shown that the introduction of Eu3+ ions into fluorophosphate glass with a small amount of phosphate decreases the Landau-Placzek ratio. Based on the analysis of the optical absorption and x-ray scattering spectra, the grouping of the Eu3+ ions with the phosphate groups is demonstrated. Applying the capture volume model, the maximum concentration of the Eu3+ ions in the phosphate environment is estimated to be 1.05x1018cm-3. It is found that the capture volumes of the Eu3+ located in the phosphate and mixed environment differ by two orders of magnitude, which approves the discussion in terms of the doped ion segregation.