Correlation betweenEu151Mössbauer isomer shift and Judd-OfeltΩ6parameters ofNd3+ions in phosphate and silicate laser glasses

Abstract

${}_{}{}^{151}{}_{}{}^{}\mathrm{Eu}$ Mössbauer effect measurements were carried out for various silicate and phosphate laser glasses doped with ${\mathrm{Eu}}^{3+}$ ions instead of ${\mathrm{Nd}}^{3+}$, for which Judd-Ofelt ${\mathrm{\Omega }}_{\mathit{t}}$ parameters are known. The isomer shift (IS) for the silicate glasses decreased with an increase in the electronegativity of the network-modifying alkali and alkaline-earth metal ions, indicating a decreased 6s electron density of the rare-earth ${\mathit{R}}^{3+}$ ions, i.e., covalency of the R-O chemical bond. On the other hand, in phosphate glasses the IS increased with increased electronegativity. Among three ${\mathrm{\Omega }}_{\mathit{t}}$ parameters of ${\mathrm{Nd}}^{3+}$, ${\mathrm{\Omega }}_6$, which dominates the radiative transition probability and branching ratio of the 1.3 and 1.06 μm emissions, showed a good correlation with the IS of ${\mathrm{Eu}}^{3+}$ ions in the corresponding glasses, independent of compositions. The results were explained by the more sensitive dependence of the Ξ(s,t) terms in ${\mathrm{\Omega }}_6$ on the overlap integrals of 4f and 5d orbitals of rare-earth ions, compared with that in ${\mathrm{\Omega }}_2$, which is sensitive to the odd-parity terms of the crystal field, ${\mathit{A}}_{\mathrm{sp}}$.