Redox equilibrium of samarium ions doped in Al_2O_3-SiO_2 glasses

摘要

Redox reaction of samarium ions doped in Al_2O_3-SiO_2 glasses, prepared by a rapid cooling technique of the melts, was examined by the measurement of the optical absorption and fluorescence properties. It was found that the doped samarium ions are easily reduced and oxidized by heating in H_2 and O_2 gases, respectively. The redox kinetics of samarium in the H_2 and O_2 atmospheres obey good first-order kinetics. The activation energy for the Sm~(3+) reduction in the 10Al_2O_390SiO_2 glass was estimated to be ～70 kJ/mol, which decreased with the increasing Al_2O_3 content. On the other hand, the activation energies for the oxidation were ～90 kJ/mol, which only slightly depends on the glass composition. In these glasses, the samarium ions are preferentially surrounded by the Al-O polyhedra, where the oxygen ions are easily removed to form defect centers. It was concluded that the movement of the oxygen ions in the Al-O polyhedra determine the redox equilibrium of the samarium ions.