Analysis of the thermal treatment effects of gadolinium-containing hydroxyapatite by EPR method

Abstract

Hydroxyapatite (HAp)-based materials doped with rare earth elements (REE) have shown ap-plications as biomaterials, lighting emitting materials, scintillating materials, in vivo imaging probes, and thermoluminescent dosimeters. Gadolinium-containing calcium phosphates are promising contrast agents for various bioimaging modalities. In this work, hydroxyapatite materials with gadolinium ion impurities with a 0.44 mol.% concentration were obtained by wet chemical precipitation. Samples after chemical synthesis (as-dried) and heat treatment were studied using electron paramagnetic resonance (EPR) spectroscopy in continuous wave and pulsed modes. Analysis of the EPR spectra made it possible to establish the incorporation of Gd3+ ions in the structure of HAp in two calcium positions with different parameters of the spin Hamiltonian. Heat treatment of samples at a T = 1300◦ C leads to a significant change in the EPR spectra of Gd3+ ions with a decrease of the uncontrolled nitrate anion centers (synthesis by-product) concentration.