Effect of boron oxide addition on the Nd 3+ environment in a Nd-rich soda-lime aluminoborosilicate glass

Abstract

The environment of Nd 3+ ions has been studied using optical absorption spectroscopy and EXAFS at the Nd L 3-edge, in a series of soda lime aluminoborosilicate glasses with increasing B 2O 3 content. The proportion of BO 4 units has been determined by 11B MAS NMR in an equivalent glass series with La 3+ ions replacing the majority of Nd 3+ ions, and complementary information has been obtained by measuring the Nd 3+ decay fluorescence times in these latter glasses. In these glasses with low Al 2O 3 content, the R′ ratio, with R′ = [Na 2O exc ] / [B 2O 3] and [Na 2O exc ] = [Na 2O] − [Al 2O 3] − [ZrO 2], plays a key role in controlling the structural organization and crystallization resistance, in a similar way as the R ratio in the Dell and Bray model of sodium borosilicate glasses. At R′ > 0.5, the Nd 3+ ions are located in a mixed silicate–borate environment and, by slow cooling of the melt, they tend to crystallize within a silicate apatite phase close to the Ca 2Nd 8(SiO 4) 6O 2 composition. At R′ < 0.5, the structural results are compatible with Nd 3+ ions located in a borate-type environment (not excluding Si neighbors), and, by slow cooling of the melt, they segregate with Ca 2+ ions within a Si-depleted separated borosilicate phase.