The aim of the present report is the study of states of Co in Co-containing sodium-silicate glasses after Na⁺-K⁺ ion exchange. The base binary 20Na₂O-80SiO₂ (in mol.%) glasses containing 0.5 wt.% CoO were studied. Polished plates approximately 0.4 mm thickness were prepared. The plates were immersed in a molten salt KNO₃ for periods of time (T_p) varying from 5min to 7h at 450 K. Some samples were annealed after ion exchange at 600 ⁰C for 24h in the H₂ atmosphere. The asymmetric EPR line with crossing-base g=4.4 ±0.1 and DH_pp~100 mT was observed at 4.2 K for the samples before an ion exchange and was attributed to Co²⁺ ions in distorted octahedal environment. The intensity of EPR line decreases with increasing Tp. New EPR line with g=2.31±0.02 is observed along with the g=4.4 line at 4.2K. Its width (DH_pp~10-25 mT) depends on T_p. The g=2.31 line is not observed above 77 K. According to literature data we attribute the g=2.31 signal to Co¹⁺ ions. The small width of this line is associated with exchange interactions between ions Co¹⁺ which form clusters . We assume the existence of Co²⁺®Co¹⁺ transition during the Na⁺® K⁺ ion exchange process. Starting from Tp=1 h and T_ht>5h the single line with g~2.22 and DH_pp~30-40 mT was observed at room temperature. The dependence of the width and intensity of this line on measurement temperature indicates its superparamagnetic origin. An additional shoulder at 265 mT which appears at 4.2K for the samples with T_p>1 h and T_ht~15h indicates the formation of ferromagnetic particles of metallic Co . Optical absorption spectra and TEM of the samples confirm the formation of nano-particles of metallic Co in ion-exchange layers of heat-treated sodium- silicate glasses doped with CoO.

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