Link between optical spectra, crystal-field parameters, and local environments of Eu3+ ions in Eu2O3-doped sodium disilicate glass

Rare-earth-doped glasses are key materials for optical technology due to the luminescent properties of 4f(n) ions. The crystal-field model describes the effect of local environment on transitions between 4f electrons. We present a detailed modeling study of the optical spectra of sodium disilicate glass, 33Na(2)O center dot 67SiO(2), doped with 0.2% and 1.0 mol% Eu2O3. This study uses very large molecular dynamics models with up to 100 Eu3+ ions, the superposition model for covalent and overlap effects on crystal-field parameters, and realistic values for homogeneous linewidth broadening. The simulated spectra are in reasonable agreement with experiment. The trends in F-7(J) energy levels across different Eu3+ ion sites have been examined and a very detailed analysis is presented that looks at how features of the spectra are related to features of the local environment of Eu3+ ions. Increasing the crystal-field strength S-total causes the F-7(0) energy level to decrease and causes the splitting of F-7(J) manifolds to increase, and this is due to increasing mixing of 4f wave functions. To a reasonable approximation the crystal-field strength components S-k depend on angular positions of ligands independently of distances to ligands. The former are seen to be more significant in determining S-k, which are closely related to the rotationally invariant bond-orientational order parameters Q(k). The values of S-2 are approximately linear in Q(2), and the values of Q(2) are higher for fivefold than sixfold coordinated rare-earth ions. These results can be of importance for efforts to enhance the local environment of rare-earth ions in oxide glasses for optical applications.