Quenching of the Eu(3+) Luminescence by Cu(2+) Ions in the Nanosized Hydroxyapatite Designed for Future Bio-Detection

The hydroxyapatite nanopowders of the Eu(3+)-doped, Cu(2+)-doped, and Eu(3+)/Cu(2+)-co-doped Ca(10)(PO(4))(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 (5)D(0) → (7)F(2) transition is the most intense transition. The Eu(3+) ions occupied two independent crystallographic sites in these materials exhibited in emission spectra: one Ca(1) site with C(3) symmetry and one Ca(2) sites with C(s) symmetry. The Eu(3+) emission is strongly quenched by Cu(2+) ions, and the luminescence decay time is much shorter in the case of Eu(3+)/Cu(2+) co-doped materials than in Eu(3+)-doped materials. The luminescence quenching mechanism as well as the schematic energy level diagram showing the Eu(3+) emission quenching mechanism using Cu(2+) ions are proposed. The electron paramagnetic resonance (EPR) technique revealed the existence of at least two different coordination environments for copper(II) ion.