Novel use of molecular dynamics simulation in studying structure–property relationships in the solid infrared laser medium Na+–Er3+β″-alumina

Abstract

X-Ray diffraction studies have been made of the crystalline luminescent material Na⁺–Er^{3 +}β″-alumina for three different erbium ion concentrations; equivalent to 100, 72 and 26% substitution of Na⁺ ions (Na_1+y–3xEr_xMg_yAl_11–yO₁₇, for x= 0.56, 0.40 and 0.14, respectively, and y= 2/3). The results form thereafter a structural basis for molecular dynamics (MD) simulations, which, in turn, are used to calculate crystal-field parameters needed for Judd–Ofelt analyses of the optical absorption spectra. The Er³⁺ ions behave somewhat differently from other rare-earth ions in the Na⁺β″-alumina host in that they can occupy two different sites in the conduction plane. Judd–Ofelt intensity parameters are calculated using a point-charge model for different concentrations and temperatures, and agree well with experimentally determined parameters. This agreement is because the local instantaneous distortions around the rare-earth ions are properly accounted for when using atomic positions taken from an MD simulation.