Laser-Induced Crystal Structure Stabilization and Europium (III) Doping of Hydroxyapatite Nanoparticles via Pulsed Liquid Fragmentation

This study aims to develop a method for the heterovalent doping of hydroxyapatite (HA) with europium (III) ions using laser fragmentation of a micropowder in a liquid medium. The samples examined after laser fragmentation of the hydroxyapatite micropowder in liquid exhibited ultrathin nanosheets (with an approximate thickness of 2–5 nm) while retaining the hydroxyapatite crystal structure; furthermore, when the process is carried out in a europium nitrate solution, it leads to the preferential incorporation of europium (III) ions into Ca(I) sites. The phase homogeneity and structural evolution of the fragmentation-derived samples were investigated by Raman and FTIR spectroscopy. Raman spectroscopy revealed that laser treatment of the HA micropowder for 30 min in the presence of 2 mol% europium nitrate (sample Eu2%-HA) modifies the crystal lattice symmetry. Conversely, the FTIR Weiner-Shemesh crystallinity index increased reflecting ordering within the basal planes. The incorporation of Eu3+ ions was confirmed by fluorescence spectroscopy supporting the predominant stabilization of europium at the Ca(I) site. Dynamic light scattering, atomic force microscopy, and transmission electron microscopy combined with energy-dispersive X-ray spectroscopy mapping were used to investigate particle morphology and assess elemental homogeneity and dopant distribution.