Persistent spectral hole burning studies in europium doped sodium silicate and borosilicate glasses

Spectroscopic studies confirmed the coexistence of Eu³⁺ and Eu²⁺ in sodium silicate and borosilicate glasses doped with europium. Persistent spectral hole burning was observed up to room temperature. Multiple hole burning was possible with moderate laser powers. When the glass composition was modified by adding 4–5% yttrium oxide, hole retention capability, hole burning efficiency and hole density also increased in both silicate and borosilicate glasses. Hole burning is due to a charge exchange between the Eu³⁺ and its environment. Certain defect centers, which were identified by electron spin resonance measurements, contributed to the formation of stable holes in the borosilicate glass.