Abstract:
The stability of KCl single crystals doped with sodium impurity ions was analyzed for the first time using absorption and luminescence spectroscopy methods. An indicator for detecting the central position of the sodium ion in the cation lattice site of a KCl–Na single crystal is the optical absorption bands induced by X-ray radiation with maxima at 6.35 and 3.5 eV (respectively, interstitial ions and chlorine atoms localized near impurity Na$^+$ ions), as well as characteristic luminescence at 2.8 eV and 3.1 eV of exciton-like formations created by recombination near single Na$^+$ or pair Na$^+$–Na$^+$ impurity ions, respectively. It has been shown that in KCl : Na crystals stored for a long time at room temperature, Na$^+$ ions leave the regular cation sites and form nano-sized clusters. However, subsequent quenching of the “decayed” crystal at high temperatures (400–700$^\circ$ C) leads to partial reverse incorporation of sodium ions into the cation sites of the KCl:Na lattice. With increasing quenching temperature, the degree of restoration increases and reaches saturation (80% of the characteristics of freshly grown crystals).
Keywords:KCl : Na single crystal, decay of KCl : Na – precipitation of sodium ion, thermal quenching – restoration of the KCl : Na lattice, X-irradiation, near-sodium radiation defects and luminescence.
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