Preferential site occupancy of Eu3+ ions in strontium hydroxyapatite nanocrystalline - Sr10(PO4)6(OH)2 - structural and spectroscopic characterisation.

Strontium hydroxyapatite (Sr10(PO4)6(OH)2) nanopowders doped with Eu3+ ions were synthesized via a microwave-stimulated hydrothermal method and were heat-treated in the temperature range of 450-650 °C for 3 h. The concentration of Eu3+ ions was set in the range of 0.5-5 mol% to investigate the site occupancy preference. The structural and morphological properties of the obtained samples were determined via XRD (X-ray powder diffraction) and TEM (transmission electron microscopy) techniques, as well as IR (infrared) and Raman spectroscopy. Nanoparticles were obtained in the range of 35-85 nm as a function of dopant concentration and sintering temperature. The luminescence properties of Eu3+ ion-doped Sr10(PO4)6(OH)2, depending on dopant concentration and sintering temperature, were investigated. The Eu3+ ion occupied one site (C3 (Sr1)) of Sr2+ cations in the Sr10(PO4)6(OH)2 matrix, providing only one emission site, as results from luminescence spectroscopy data confirmed by the Rietveld refinement. A weak broad emission was observed with a peak at about 425 nm, corresponding to the 4f65d1 → 4f7 (8S7/2) transition of Eu2+ ions. The simplified Judd-Ofelt (J-O) theory was performed and a detailed analysis in connection with observed structural and spectroscopic measurements was carried out and has been described herein.