Redox equilibrium of samarium ions doped in Al2O3-SiO2 glasses

Redox reaction of samarium ions doped in Al2O3-SiO2 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 H2 and O2 gases, respectively. The redox kinetics of samarium in the H2 and O2 atmospheres obey good first-order kinetics. The activation energy for the Sm3+ reduction in the 10Al2O390SiO2 glass was estimated to be ∼70 kJ/mol, which decreased with the increasing Al2O3 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.