Rare-earth-doped glasses are key materials for optical technology due to the luminescent properties of 4fn 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, 33Na₂O•67SiO₂, 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 7FJ 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 Stotal causes the 7F₀ energy level to decrease and causes the splitting of 7FJ manifolds to increase, and this is due to increasing mixing of 4f wave functions. To a reasonable approximation the crystal-field strength components Sk depend on angular positions of ligands independently of distances to ligands. The former are seen to be more significant in determining Sk, which are closely related to the rotationally invariant bond-orientational order parameters Qk. The values of S₂ are approximately linear in Q₂, and the values of Q₂ 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. Copyright © 2011 American Physical Society.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - Sep 2011|
crystal field theory
rare earth elements
Electron energy levels