Contribution of neodymium optical spectroscopy to the crystal growth study of a silicate apatite in a glassy matrix

Neodymium migration from the glass to the unique crystal phase, Ca(2)Nd(8)(SiO(4))(6)O(2) apatite, was followed by absorption ((4)I(9/2) -> (2)P(1/2) transition) and emission ((4)F(3/2) -> (4)I(9/2) transition) spectroscopy in aluminoborosilicate glass-ceramics prepared at various temperatures. Comparison of these glass-ceramics showed that ordering of Ca(2+) and Nd(3+) ions in the 6h and 4f sites of the silicate apatite structure progressively increased when the crystallisation temperature T(c) is raised from 950 to 1450 K. Taking advantage of the emission quenching in apatite crystals due to high Nd(3+) ions concentration, the residual glass surrounding these crystals was probed. The highest neodymium depletion in the glassy phase was obtained after heat treatment at T(c) = 1300 K. Neodymium was found to be a nucleation agent for apatite crystallization. The nucleation mechanism of this phase at low temperature begins by the migration of Nd(3+) ions from glass sites to the apatite 4f sites that are structurally close. At higher temperature, due to the increasing thermal energy available during crystal growth, the proportion of Nd(3+) ions incorporated in the apatite 6h site increased. (c) 2007 Elsevier B.V. All rights reserved.