Spatially resolved optical studies ofF-center diffusion in KBr crystals

Abstract

Spatially resolved optical studies of F-center diffusion during and after the photothermal F→X color center conversion have been performed by optical scanning and holographic methods in electrolytically colored KBr crystals. Average velocities and diffusion coefficients of F centers have been determined for Gaussian and periodical spatial exposing light intensity distributions. A strong influence of the light intensity gradient has been found on F-center diffusion. It manifests itself by a rapid increase of the effective diffusion coefficient when the light intensity gradient is decreased. This behavior allowed us to explain the observed peculiarities of the holographic recording and to make the suggestions to optimize the recording.

Formation of the defect halo of swift heavy ion tracks in LiF due to spatial redistribution of valence holes

“…We used the lowest reported value of the barrier realizing for photo excited F‐centers ( F *‐centers) in alkali halides (0.2 eV in KCl, KBr) for an estimation. This barrier is comparable to the diffusion barrier of H‐ and I‐centers 33, 34. We obtained that, due to a very short life‐time of the transient ionized state of the lattice (10 −14 –10 −11 s), even for this extremely low diffusion barrier the diffusion lengths of F‐centers is too short to describe the observed difference between the radial distributions of valence holes and F‐centers detected in a track.…”

Highly charged ion induced nanostructures at surfaces by strong electronic excitations

“…6(a)). The H-centers are highly mobile in the crystal, even at room temperature, whereas F-centers are immobile in their ground state, but mobile in their excited state (F * -centers) [55]. The F-centers can be excited either by the primary electrons or by co-excitation with visible light within the F-center absorption band [56].…”

Surface Topography Dependent Desorption of Alkali Halides

“…It has been found previously that the ground state F centers are immobile, whereas excited and relaxed F ‫ء‬ centers can easily diffuse in the crystal [13][14][15]. In the recent paper Salminen et al [15] have demonstrated that initially uniform F center concentration in electrolytically colored KBr crystal can be modulated, if the crystal is exposed to 518 nm light which is within the F-center absorption band.…”

“…In the recent paper Salminen et al [15] have demonstrated that initially uniform F center concentration in electrolytically colored KBr crystal can be modulated, if the crystal is exposed to 518 nm light which is within the F-center absorption band. The light induces the F-center diffusion and aggregation.…”

“…Apart from the F-H annihilation a few other reactions may, in principle, occur in the crystal bulk: aggregation of F ‫͒ء͑‬ centers into X centers [15] and reactions of the H center with the F ‫ء‬ or X. However, transient F ‫ء‬ concentration (resulting from the primary excitation cascade) is of the order 10 18 cm 23 [2] while the stored F concentration is estimated as ϳ10 19 cm 23 .…”