Influence of europium doping on the crystalline and photoluminescence properties of hydroxyapatite nanofibers

Pure hydroxyapatite (HAp) and europium-doped hydroxyapatite (HAp_xEu) at 2 % and 2.5 mol% were synthesized using the microwave-assisted hydrothermal method. The morphological and structural properties were analyzed by Scanning Electron Microscopy (SEM), High Resolution Transmission Electron Microscopy (HRTEM), X-ray Diffraction (XRD) and, Rietveld Analysis respectively. While the vibrational analyses were done using Fourier Transform Infrared Spectroscopy (FTIR), Raman Spectroscopy and Photoluminescence Spectroscopy (PL). The X-ray diffraction analyzes revealed the presence of the hydroxyapatite phase as the only crystalline component present in all the samples, while that Rietveld analysis indicates that Eu³⁺ has been inserted into the crystalline lattice without causing affectation. Eu³⁺ doping promotes preferential growth in the [001] direction of the structure. In addition, the doped samples show an emission spectrum characteristic of the electronic transition ⁵D₀ →⁷F₂ observed at 613 nm, which is related to the substitution of the Eu ions in the calcium Ca¹⁺ sites in the apatite structure.