Effect of irradiation parameters on defect aggregation during thermal annealing of LiF irradiated with swift ions and electrons

Abstract

Absorption spectroscopy were performed to study the effects of thermal annealing on the aggregation of color centers in LiF crystals irradiated with different ions between carbon and uranium of megaelectron volt-gigaelectron volt energy. The beam parameters such as energy, energy loss, and fluence have a pronounced influence on the initial defect composition and concentration as well as their evolution upon thermal annealing. A distinct phenomenon was observed, viz., the enhancement of F n centers for annealing temperatures between 500 and 700 K, followed by Li colloid formation above 700 K. The phenomenon requires specific irradiation conditions whereas the formation of Mg colloids from Mg impurities occurs in all irradiated crystals. The mechanisms of annealing and colloid formation are discussed.

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

“…High quality LiF crystals grown from the melt in inert atmosphere (Korth Kristalle, Germany) were used in the experiments (see Ref. 15, 16 for details). X‐ray luminescence analysis detected Mg (20 ppm), Na (1 ppm), and Cl (1 ppm) trace elements in these crystals.…”

“…The thicknesses of all samples were larger than the ranges of applied ions 17. In addition to the room temperature irradiations, some samples were irradiated at 8 K in a cryostat installed in the beam line 15, 16.…”

“…Realizing this possibility we found the large difference between the spatial distributions of color centers detected in tracks of different ions (C, Ti, Au, U, Pb) in LiF crystals 15, 16 and the initial spatial distributions of valence holes in tracks of these ions calculated by the well tested Monte‐Carlo (MC) code by the time of finishing of ionization cascades. The detailed analysis of this difference led us to conclusions about parameters of the relaxing holes ensemble in a track, namely: the conversion efficiency of created holes into stable color centers ( β = 0.01–0.04), and the mean diffusion coefficient of hot holes in SHI tracks at the picosecond time scale after the projectile passage ( D h = 0.016–1.4 cm 2 s −1 ).…”

Color centers and nanodefects in LiF crystals irradiated with 150MeV Kr ions

“…Thermal stability of various defects in LiF irradiated with heavy ions depends on the ion energy loss and fluence [19]. During thermal annealing two different processes take place: (1) the decomposition of V 3 centers with H center production; (2) diffusion of single F centers with the following formation of complex electron color centers according to the reactions F + F n ?…”

Irradiation effects in CaF2 probed by Raman scattering

“…The lower energy could explain the defect stability under illumination with the red (1.96 eV) laser. Also, such processes had already been proposed for LiF samples thermally annealed after ion or electron irradiation . As the temperatures were increased in this study, it was shown that the annihilation of single centers first occurred (below 500 K), followed by the aggregation of more complex center (500–600 K) and the formation of larger Li colloidal particles (600–700 K), culminating into their reduction/disappearance (above 700 K).…”