Structural modification of nanohydroxyapatite Ca(PO)(OH) related to Eu and Sr ions doping and its spectroscopic and antimicrobial properties.

The Eu and Sr ions co-doped hydroxyapatite nanopowders (Ca(PO)(OH)) were synthesized via a precipitation method and post heat-treated at 500 °C. The concentration of Eu ions was established in the range of 0.5-5 mol% to investigate the site occupancy preference. The concentration of Sr ions was set at 5 mol%. The structural and morphological properties of the obtained materials were studied by an X-ray powder diffraction, a transmission electron microscopy techniques and infrared spectroscopy. As synthesized nanoparticles were in the range of 11-17 nm and annealed particles were in the range of 20-26 nm. The luminescence properties in dependence of the dopant concentration and applied temperature were investigated. The D → F transition shown the abnormally strong intensity for annealed materials connected with the increase of covalency character of Eu-O bond, which arise as an effect of charge compensation mechanism. The Eu ions occupied three possible crystallographic sites in these materials revealed in emission spectra: one Ca(1) site with C symmetry and two Ca(2) sites with C symmetry arranged as cis and trans symmetry. The antibacterial properties of Eu and Sr ions doped and co-doped hydroxyapatite nanopowders were also determined against Gram-negative pathogens such as Pseudomonas aeruginosa, Klebsiella pneumoniae and Escherichia coli. Obtained results suggest that both europium and strontium ions may implement antibacterial properties for hydroxyapatites. In the most cases, better antibacterial effect we noticed for dopants at 5 mol% ratio. However, the effect is strongly species- and strain-dependent feature.