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

Abstract

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 (⁸S_7/2) 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.