The hydroxyapatite nanopowders of the Eu3+-doped, Cu2+-doped, and Eu3+/Cu2+-co-doped Ca10(PO4)6(OH)2 were prepared by a microwave-assisted hydrothermal method. The structural and morphological properties of the products were investigated by X-ray powder diffraction (XRD), transmission electron microscopy techniques (TEM), and infrared spectroscopy (FT-IR). The average crystal size and the unit cell parameters were calculated by a Rietveld refinement tool. The absorption, emission excitation, emission, and luminescence decay time were recorded and studied in detail. The 5D0 → 7F2 transition is the most intense transition. The Eu3+ ions occupied two independent crystallographic sites in these materials exhibited in emission spectra: one Ca(1) site with C3 symmetry and one Ca(2) sites with Cs symmetry. The Eu3+ emission is strongly quenched by Cu2+ ions, and the luminescence decay time is much shorter in the case of Eu3+/Cu2+ co-doped materials than in Eu3+-doped materials. The luminescence quenching mechanism as well as the schematic energy level diagram showing the Eu3+ emission quenching mechanism using Cu2+ ions are proposed. The electron paramagnetic resonance (EPR) technique revealed the existence of at least two different coordination environments for copper(II) ion.
Keywords: EPR spectroscopy; apatite; cooper ions; europium ions; photoluminescence spectroscopy.