V. M. Lisitsyn

Transient optical transmission changes induced by pulsed electron radiation in commercial crown silicate glasses

Abstract We report on results of time-resolved induced optical absorption measurements in commercial crown silicate glass K8 (similar to Schott BK7 glass) and its radiation-resistant counterpart K108 under 0.25-MeV pulsed electron radiation. The spectra have been obtained in a wavelength range 280–1100 nm on a time interval 10 ns–1 s after the end of a 20-ns pulse. In contrast to behavior of stable defects, the efficiency of non-stationary color centers’ generation in the long-wavelength spectrum range is similar for both standard and radiation-resistant glasses. The characteristic time for transmission recovery in the visible range at room temperature was found to be about 100 μs. Based on the Kramers–Kronig relations we have estimated transient refractive index changes. For the same radiation dose such changes can be two orders of magnitude higher than those observed in stationary conditions.

Impurity cathodoluminescence of oxygen-containing LiF crystals

Cathodoluminescence of oxygen-containing LiF crystals (LiF-O, LiF-O,OH, LiF-WO3) is studied by pulsed spectrometry with nanosecond resolution upon excitation of crystals by a single electronbeam pulse at 15 K.

Evolution of primary radiation defects in ionic crystals

Using pulsed spectrometry with nanosecond time resolution, we have studied the characteristics of creation of induced defects and the relaxation of such defects in the initial stage in ionic crystals, using as examples ten alkali halide crystals with sc and fcc lattices and an MgF2 crystal in the temperature range 12.5–500 K. We present the transient absorption spectra, the relaxation kinetics for the induced defects over a broad temperature range, the dependences of the creation and relaxation on the excitation flux density. The results of our investigations are generalized in tables and, in the form of the most characteristic dependences, in figures. We describe the model developed for evolution of primary defects, taking into account the main general characteristics observed experimentally and the results of mathematical modeling based on it, which allowed us to put together a general picture for the series of processes determining the evolution of primary defects.

The efficiency of formation of primary radiation defects in LiF and MgF2 crystals

Processes of radiation formation of primary defects—F centers and self-trapped excitons—in lithium and magnesium fluorides, which have crystal lattices of different types and similar widths of the band gap and valence band, have been studied in a wide temperature range (11–500 K). It is shown that, along with qualitative similarity of the regularities of formation of the defects under study, LiF and MgF2 crystals are characterized at low temperatures (11–100 K) by different relationships between the energy dissipation channels for self-trapping electronic excitations and the types of self-trapped excitons arising.

High-current nanosecond electron beams for probing the parameters of solids

Special features and prospects of using high-current nanosecond electron beams for probing the parameters of solids are examined. Of all the variety of signals carrying information on the characteristics of the test object under electron-beam excitation, the potentialities and features of pulsed cathodoluminescence of dielectric and semiconducting materials and of optical absorption (emission) of atoms evaporated by electron beams from metal surfaces or those of conducting rocks are discussed in detail.

Short-lived primary radiation defects in LiF crystals

The spectral and kinetic parameters of electron-pulse-initiated transient absorption and emission of LiF crystals were studied using pulsed spectrometry with a nanosecond time resolution. The measurements were performed in the spectral region of 6 eV, the temperature range of 11–150 K, and within 10−8–10 s after the termination of an electron pulse. It is shown that the electron-pulse irradiation not only gives rise to F, Vk, and H centers in the LiF crystal but also to certain short-lived defects of two types that differ in the spectral positions of the absorptive and radiative transitions, the lifetime, and the temperature dependence of the production efficiency. Defects of type I feature absorptive transitions at 5.5 and 5.1 eV and a radiative transition at 5.8 eV, whereas the absorptive transitions at 5.3 and 4.75 eV and a radiative transition at 4.4 eV are characteristic of type-II defects. It is found that a variation in the ratio between the concentrations of the different types of short-lived centers in the range of 11–150 K does not affect the quantum efficiency of the F centers. It is assumed that the observed centers are self-trapped excitons of various types.

Radiation-induced nonsteady-state absorption in multicomponent silicate glasses

Nonsteady-state absorption spectra have been studied in multicomponent glass F1 of the flint group and its radiation-stable analog F101, induced by excitation with an electron pulse 20 ns wide having particle energy 0.25 MeV. The measurements were made in the 300-600 nm spectral region on the time interval 10 ns-1 sec after the end of the irradiation pulse. It is found that the formation efficiency of unstable color centers with absorption bands in this spectral region is approximately identical for both types of glasses. After the pulse stops acting, the absorption in the entire spectral range decreases at approximately the same rate, so that the shape of the nonsteady-state induced absorption spectra shows little variation. The effect of the cerium ions that are present in F101 as a protector additive manifests itself in times much greater than the pulse width.

Formation of near-defect excitons in alkali-halide crystals

Pulsed-spectrometric research shows that the presence of defects, including those that are electrically neutral with respect to the crystal lattice, has a significant influence on the distribution of the radiation-induced electron excitations. This is evident in the electron-excitation sink in the vicinity of defects and the formation of localized excitons around impurities in ionic crystals. This influence of defects on the electron-excitation distribution is probably due to deformation of the lattice in the region of the defect. It is shown that, in the region of the defect, there is oscillating potential relief, the presence of which leads to the capture of charge carriers and their localization in this region. Lattice distortion because of deformation in the region of the defect changes the mutual distribution of the ion pairs. This creates conditions for the effective conversion of electronic excitations to localized near-defect dihalide excitons, which are different from those created in an ideal lattice.

A comparative analysis of the spectral characteristics of triplet self-trapped excitons and F2 centers in alkali halide crystals

A comparative analysis of the spectral characteristics of self-trapped excitons (STE) and F2 centers in the states with the same spin multiplicity is carried out. Based on the analysis, a criterion for the separation of the triplet-triplet (T-T) absorptive transitions in the electronic and hole components of the STE in any alkali halide crystal is proposed. It is concluded that inhomogeneities in the form of a homological cation or anion impurity in the nearest coordination shells of the spatial position of the STE, rather than hole, affect the spectral position of the T-T transitions in the electron component of the STE.