Optical studies on the conversion from Ag+ to Ag− centers by the electrolytic coloration in NaCl and KCl crystals

We have investigated optical spectra of uncolored and electrolytically-colored NaCl:Ag+ and KCl:Ag+ crystals at low temperatures. In the uncolored crystals, the several absorption bands due to the 4d10 → 4d95s transitions in Ag+ ions are observed in the energy region below the absorption edge of the host crystals. When the uncolored crystals are electrolytically colored, the absorption bands due to the Ag+ centers decrease and the C absorption band due to Ag− centers appears with the compensation for the decrease of the absorption bands due to the Ag+ centers. The fact implies that the conversion from the Ag+ to Ag− centers occurs through the electrolytic coloration. In the crystals with the Ag+ concentration below about 1018 cm−3, the conversion efficiency from the Ag+ to Ag− centers reached more than 60%. The conversion processes from the Ag+ to Ag− centers are discussed.