The Effect of Instability of KCl:Na Single Crystals

• Published in: Crystals (Basel) 2023-02, Vol.13 (2), p.364
• Main Authors: Shunkeyev, Kuanyshbek, Tilep, Aizhan, Sagimbayeva, Shynar, Ubaev, Zhiger, Lushchik, Aleksandr
• Format: Article
• Language: English
• Subjects: Absorption spectra; Cations; Chemical properties; Chlorine; Crystal defects; Crystal growth; Crystal lattices; Crystals; decay of a KCl:Na crystal-precipitation of sodium ions from regular sites; Excitons; High temperature; Impurities; KCl:Na single crystal; Luminescence; luminescence centers; near-sodium localized radiation defects; Optics; Point defects; Potassium chloride; Radiation; Radiation damage; Restoration; Room temperature; Single crystals; Sodium; Spectrum analysis; Stability analysis; Thermal properties; thermal quenching-restoration of the KCl:Na lattice; X-irradiation; X-rays
• ISSN: 2073-4352; 2073-4352
• DOI: 10.3390/cryst13020364

For the first time, the stability of KCl single crystals doped with sodium impurity ions was analyzed via the optical absorption and luminescence methods. Using the characteristic bands of optical absorption, as well as of X-ray and tunnel luminescence, ascribed to radiation defects and exciton-like formations localized near sodium impurity, the removal of Na+ ions from regular cation sites into nanosized clusters in KCl:Na crystals stored for a long time at room temperature was demonstrated. At the same time, the subsequent annealing of such “decayed” crystals at high temperature (400–700 °C) led to a partial incorporation of sodium impurity ions back into cation sites and the restoration of a homogeneous distribution of Na+ in the KCl:Na lattice. With an increase in the quenching temperature, the restoration degree continuously increased until it reached the saturation level (about 80% of the characteristics of a freshly grown crystal). The detectable/disappearing X-ray-induced absorption bands at 6.3 and 3.5 eV (respectively ascribed to interstitial chlorine ions and atoms localized near Na+), as well as the luminescence bands at 2.8 and 3.1 eV, typical of recombinationally generated exciton-like formations near Na+ or Na+-Na+, were the indicators of sodium ion redistribution in the crystal lattice.