Sm2+ in BAM: fluorescent probe for the number of luminescing sites of Eu2+ in BAM

In the literature it is usually assumed that the activator ion Eu2+ enters the BaMgAl10O17 (BAM) lattice substitutionally at the Ba site (the Beevers-Ross site). Recent neutron diffraction results indicate that Eu2+ ions ([Xe]4f7) do not occupy this Beevers-Ross site, but an interstitial site (anti-Beevers-Ross site) in this host material with β-alumina structure. According to recent 151Eu Mössbauer measurements however, the europium ions appear to be distributed over more than one type of sites. Since spectroscopical analysis of the broad emission band of BAM : Eu2+ does not allow a unique determination of the location of Eu2+ ions in this lattice, we have used in this work the sharp spectral lines of divalent samarium 4f–4f transitions to probe the distribution of Eu2+ ions. High resolution measurements of BAM : Sm2+ at liquid helium temperature suggest the presence of more than one site in BAM for Sm2+. Since Eu2+ and Sm2+ possess nearly identical ionic radii and chemical properties, the results from the present investigation provide additional support for the “multiple sites” hypothesis for divalent europium ions in this phosphor.