An optical perspective on the thermal-activated ionic migration state and ionic jumping distance in glass

Abstract

Ion migration is a fundamentally important process upon activation by external temperature or an electric field in ionic conductors, and it is also common in opto-functional materials like lasing glass caused by heat accumulation. It is prerequisite to investigate the thermal-driven ion migration process, analogous with the defect generation or annihilation. An optical approach with upconversion (UC) luminescence of Er³⁺ is used to reveal the ionic migration state and the jumping distance in the Na⁺-conducting glass of Yb³⁺/Er³⁺-doped SiO₂–CaO–Na₂O. The apparent break point at ∼150 °C in the intensity ratio of green and red emission versus temperature can show the ignition of Na⁺ motion, as evidenced by various characterization techniques. And this should be ascribed to a distinct non-radiative rate from the green emitting level to red emitting level versus temperature in the ionic migration state of glass. The Na⁺ jumping distance is ∼1.8 Å estimated by using the electric method, roughly coincident with the result deduced by the optical sensing approach. The dynamic migration of Na⁺ would adjust the bond angle and bond length of the Si–O bridging network and relax the mother host structure of the glass, according to the ²⁹Si nuclear magnetic resonance data. This research gives an alternative perspective on thermal-activated ion migration via an optical approach.