Rare-earth (Gd3+,Yb3+/Tm3+, Eu3+) co-doped hydroxyapatite as magnetic, up-conversion and down-conversion materials for multimodal imaging

摘要

Taking advantage of the flexibility of the apatite structure, nano- and micro-particles of hydroxyapatite (HAp) were doped with different combinations of rare earth ions (REsup3+/sup?=?Gd, Eu, Yb, Tm) to achieve a synergy among their magnetic and optical properties and to enable their application in preventive medicine, particularly diagnostics based on multimodal imaging. All powders were synthesized through hydrothermal processing at T ≤ 200?°C. An X-ray powder diffraction analysis showed that all powders crystallized in P6sub3/sub/m space group of the hexagonal crystal structure. The refined unit-cell parameters reflected a decrease in the unit cell volume as a result of the partial substitution of Casup2+/sup with smaller REsup3+/sup ions at both cation positions. The FTIR analysis additionally suggested that a synergy may exist solely in the triply doped system, where the lattice symmetry and vibration modes become more coherent than in the singly or doubly doped systems. HAp:REsup3+/sup optical characterization revealed a change in the energy band gap and the appearance of a weak blue luminescence (λsubex/sub?=?370?nm) due to an increased concentration of defects. The "up"- and the "down"-conversion spectra of HAp:Gd/Yb/Tm and HAp:Gd/Eu powders showed characteristic transitions of Tmsup3+/sup and Eusup3+/sup, respectively. Furthermore, in contrast to diamagnetic HAp, all HAp:REsup3+/sup powders exhibited paramagnetic behavior. Cell viability tests of HAp:Gd/Yb/Tm and HAp:Gd/Eu powders in human?dental pulp stem cell cultures indicated their good biocompatibility.