E. Vasil'chenko

Anion interstitials in neutron-irradiated MgO single crystals

Electron paramagnetic resonance (EPR) and high-temperature (300 –775 K) thermoluminescence of neutron-irradiated MgO single crystals were studied. Spin-hamiltonian parameters of the observed anion interstitial centres (O − molecular ion in an oxygen site by a cation vacancy—H centre) were determined. The thermal stability of anion interstitials (H centres) and other EPR-active centres was investigated. It is shown that the thermal decay of H centres is attended by a TL peak due to hole recombination luminescence at 700 K. A possible mechanism for the thermal destruction of anion Frenkel defects in MgO is discussed. c � 2001 Elsevier Science Ltd. All rights reserved.

Low-temperature creation of Frenkel defects via hot electron-hole recombination in highly pure NaCl single crystals

The creation spectrum of stable F centres (being part of F-H pairs of Frenkel defects) by synchrotron radiation of 7–40 eV has been measured for highly pure NaCl single crystals at 12 K using a highly sensitive luminescent method. It is shown that the efficiency of F centre creation in a closely packed NaCl is low at the decay of anion or cation excitons (7.8–8.4 and 33.4 eV, respectively) or at the recombination of relaxed conduction electrons and valence holes. Only the recombination of nonrelaxed (hot) electrons with holes provides the energy exceeding threshold value EFD, which is sufficient for the creation of Frenkel defects at low temperature.

Multiplication of electronic excitations and formation of radiation defects in alkali halides

The spectrum of F center creation has been measured for KBr:Tl using synchrotron radiation (12–32 eV). The creation efficiency of a stable F center is especially high at 15–17 and 28–30 eV where the absorption of one photon leads to the formation either both of an electron-hole pair and an exciton or two electron-hole pairs and an exciton. In these cases there are favourable conditions for stabilization of mobile radiation defects due to the association of interstitial halogen atoms, holes and cation vacancies.

Metastable one-halide self-trapped excitons in alkali halides

Fast (τ < 2 ns) short-wavelength emissions have been detected overlapping the continuous intraband luminescence on exciting KBr, RbBr, KCl and RbCl crystals by an electron beam. These emissions are attributed to the radiative decay of metastable one-halide self-trapped excitons. The weak 5.8 eV emission can effectively be excited in a KBr crystal in the region of the formation of excitons (6.73-7.3 eV).

Multiplication of electron excitations and the creation of stable radiation-induced defects in ionic crystals

The paper discusses the phenomenon of electron-excitation multiplication that arises when alkali halide crystals are exposed to 12–32 eV photons, with absorption of one photon followed at 8 K by the appearance of two or three electron excitations. Measurement of the spectrum of F-center generation by 6.5–32 eV photons showed that at 200–300 K, when vacancies and interstitials are mobile, the formation of stable defects is especially efficient when radiation creates a mixture of electron-hole pairs and excitons. Certain mechanisms of creation and stabilization of defects at various stages in electron-excitation multiplication are discussed.