Abstract Neodymium migration from the glass to the unique crystal phase, Ca 2Nd 8(SiO 4) 6O 2 apatite, was followed by absorption ( 4I 9/2 → 2P 1/2 transition) and emission ( 4F 3/2 → 4I 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.