NOVEL USE OF MOLECULAR-DYNAMICS SIMULATION IN STUDYING STRUCTURE-PROPERTY RELATIONSHIPS IN THE SOLID INFRARED-LASER MEDIUM NA+-ER3+ BETA''-ALUMINA

X-Ray diffraction studies have been made of the crystalline luminescent material Na+-Er3+ beta''-alumina for three different erbium ion concentrations; equivalent to 100, 72 and 26% substitution of Na+ ions (Na1+y-3xErxMgyAl11-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+ beta''-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.