Local structure and persistent spectral hole burning of Sm 2+ in silica-based fibers

Abstract

Silica-based glasses doped with Sm 2+ have been prepared by using vapor-phase axial deposition method under a reducing atmosphere. The fluorescence spectra reveal that the reduction of Sm 3+ to Sm 2+ ions is accomplished in the silica glass codoped with Al 2O 3, while the Sm 2+ ions are not incorporated into the silica glass without Al 2O 3. The effects of Al 2O 3 codopant on the coordination change around divalent rare-earth ions are discussed according to our previous studies of 151Eu Mössbauer effects. It is assumed that the divalent rare-earth ions are preferentially coordinated by Al polyhedra, resulting in the stability of the lower valence state of the rare-earth ions. Persistent spectral hole burning is also demonstrated at room temperature for the 7F 0– 5D 0 transition of Sm 2+ in the aluminosilicate glass fiber. A hole width of 6 cm −1 is much narrower than the inhomogeneous width of 100 cm −1 , leading to the ratio of inhomogeneous-to-homogeneous width of ∼40.