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.