Optical Study of Eu~(3+) Ion Embedded in (1-x)Na_2WO_4-xP_2O_5 Glasses Highlighting a Temperature Effect on its Local Environment

摘要

Tungsten-phosphate glasses doped with trivalent europium ion are synthesized and their spectroscopic properties are analyzed. Following the evolution of the ~5D_0 → ~7F_1 electronic transition in a series of various glass compositions via two rank crystal field parameters (cfp's), a slight modification of the local symmetry is evidenced in the series. Decay lifetimes of ~5D_1 and ~5D_0 levels are also analyzed. Optical properties clearly correspond to Eu~(3+) in the glassy phase. At room as well as at liquid nitrogen temperatures, the emission spectra display comparable features with prominent ~5D_0 → ~7F_2 transition. However, at 77 K, the maximum ~7F_1 splitting exhibits an increase of ≈ 20-23% for all compounds. This increase is directly connected to a change in local environment around the rare earth ion. The optical properties and the crystal field variation could be correlated with the shortness of the metal-oxygen distances produced by the pressure when cooling.