V.T. Gritsyna

X-Ray Luminescence of Defects in Spinel Single Crystals

The flareup of x-ray luminescence in spinel single crystals (MgAl2O4) depending on the time of x-ray irradiation and the decay of fluorescence depending on the time elapsed after the termination of irradiation have been investigated. These dependences were measured at different powers of the irradiation dose (power of the x-ray tube) and at different temperatures of the samples. The experimental results suggest the existence of large-size complexes of defects, which include antisite defects and impurity ions, the exchange of charge carriers between which during and after irradiation leads to luminescence of the impurity ions. Transfer of charge carriers between isolated elements of the pairs of antisite defects (not interacting with the impurity ions) leads to the formation of a competing channel of recombination luminescence in the UV region of the spectra. The decay of fluorescence attributable to transitions in the Mn2+ and Cr3+ ions depending on the time elapsed after the termination of x-ray irradiation points to the existence of various combinations of antisite defects in the surroundings of these ions.

The Origin of Radiation Resistance of Magnesium Aluminate Spinel

We propose here a new mechanism to explain the observed high radiation tolerance of magnesium aluminate compounds with crystal structures known as spinel. By using optical methods, we found that the kinetics of accumulation of optical absorption centers under different types of irradiation, as well as the kinetics of absorption decay after termination of irradiation, along with radio-luminescence processes, are consistent with a new model regarding defects and radiation damage in spinel. This model assumes the existence of spatially-correlated antisite defects in the form of dipoles: (Al 3+ tet ) + -(Mg 2+ oct ) - . These spatially-correlated point defect complexes serve as centers for annihilation of radiation-induced cation Frenkel pairs. In addition to the spatially-correlated defects, the high concentration of cation structural vacancies inherent to the spinel lattice also serves to promote high mobility of both Mg and Al interstitial species. This enhanced mobility leads to increased probability of annihilation at the dipole centers proposed in this model. Such annihilation then diminishes the probability for formation of defect clusters, dislocation loops, or amorphization of the irrradiated spinel.

Changes in the composition and optical properties of Cu and Cu 2 O nanofilms deposited on SiO 2 substrates after annealing and bombardment by argon and hydrogen ions

Copper films with a thickness of 10, 15, 27, and 45 nm deposited on quartz glass substrates are oxidized in an air flow at different temperatures. The compositions of the films are determined by X-ray photoelectron spectroscopy and calculated from the optical absorption spectra using an original method developed by us. The influence of the bombardment of the samples by argon and hydrogen ions on the optical properties and composition of the films is studied. The experimental depth of Cu2O film reduction is three times higher than the calculated penetration depth of H+ ions. The rate of film sputtering by H+ ions with the energy 300 eV increases with an increase in the film thickness due to the loose structure of the oxidized layer.l

Radio-Luminescence of Defects and Impurity Ions in Magnesium Aluminates Spinel Crystals

The investigations of radio-luminescence (RL) in magnesium aluminates spinel crystals at variation of the time, intensity of X-irradiation and temperature of sample were provided. There were registered three prominent RL bands related to electron-hole recombination process at anti-site defects, emission of Mn2+-ions and emission of Cr3+-ions. The kinetics of the growth of indicated RL emissions show the competing processes of the capture of free charge carriers generated at irradiation by intrinsic defects and impurity ions.

Infrared spectroscopy studies of magnesium aluminates spinel crystals

The reflectance and transmittance spectra for magnesium aluminates spinel single crystals MgO•nAl2O3 and ceramics in the IR spectral range were measured to investigate the nature of vibration modes of constituent ions and incorporated hydrogen. Besides of the earlier observed bands at 545, 710, and 835 cm-1 we registered also two bands 1440 and 1670 cm-1 in single crystals grown by different methods and in spinel optical ceramics. The existence of these bands was supported by measurements of non-stoichiometric spinel crystals and crystals doped with transition metals. The variation of intensity of registered bands in spinel of stoichiometric and non-stoichiometric compositions and spinel ceramics was interpreted in terms of vibration modes of divalent and trivalent cations in different coordination, particularky, at the spatially correlated anti-site defects.

Radio-luminescence of defects and impurity ions in magnesium aluminates spinel

The investigations of radio-luminescence (RL) in magnesium aluminates spinel crystals at variation of the time, intensity of X-irradiation and temperature of sample were provided. There were registered three prominent RL bands related to electron-hole recombination process at anti-site defects, emission of Mn2+-ions and emission of Cr3+-ions. The kinetics of the growth of indicated RL emissions show the competing processes of the capture of free charge carriers generated at irradiation by intrinsic defects and impurity ions.