Influence of Li+ ions on the physicochemical properties of nanocrystalline calcium–strontium hydroxyapatite doped with Eu3+ ions

Abstract

In the present study, nanocrystalline Ca–Sr hydroxyapatites structurally modified with Li⁺ ions as well as co-doped with Eu³⁺ ions were prepared by the hydrothermal method assisted by heat treatment. The structural and morphological properties of the studied materials were determined by using XRPD (X-ray powder diffraction), ATR-FTIR (attenuated total reflectance-FTIR spectroscopy) and SEM (scanning electron microscopy) techniques. According to Rietveld analysis, the crystallite sizes were calculated to be in the range of 48–67 nm and were close to the value obtained by SEM. Based on X-ray diffraction and IR absorption, the structural changes after the substitution of divalent calcium ions by other cations in the apatite crystal lattice were identified. The changes appeared as a shift of the (0 0 2) plane position as well as a shift of the PO₄³⁻ and OH⁻ bands. In this case, a possible charge compensation mechanism was investigated based on the Kröger–Vink notation. The investigation of the luminescence properties (emission, emission excitation and emission kinetics) of the studied materials as a function of Li⁺ ion concentrations was carried out. The luminescence behavior of Eu³⁺ ions in the samples was analyzed by the Judd–Ofelt (J–O) theory, and the J–O parameters were estimated and discussed.