Nanosized luminescent hydroxyapatite doped with terbium: synthesis and characterization

The aim of this work is to synthesize a new nanostructured biocompatible material with a high ability to X-ray-induced luminescence. Terbium-doped hydroxyapatite known for its biocompatibility and non-toxicity was synthesized in two ways: 1) by precipitation of Ca2+ and Tb3+ ions with (NH4)2HPO4 solution in the presence of various biocompatible modifiers (CTAB, PEG-2000, trisodium citrate dihydrate); 2) by cationic substitution of hydroxyapatite in the presence of the same modifiers at pH 4 and pH 6. The stoichiometric ratio (Ca+Tb)/P in the initial solutions was maintained at the level of biological hydroxyapatite. Based on the results of DLS, ELS, and X-ray-induced luminescence studies, it was found that the sample with the best key properties, such as ζ-potential and X-ray-induced luminescence, was the sample of hydroxyapatite doped with 5% (mol), synthesized by co-precipitation procedure in presence of trisodium citrate dihydrate. Further studies by TEM, FTIR, FT-NIR, TG/DTG/DTA, XRD, low-temperature nitrogen adsorption-desorption, and ICP-AES confirm that the sample has a surface functionalized with citrate groups, which causes high colloidal stability and can provide high adsorption potential. The value of the (Ca+Tb)/P ratio is 2.21 (wt %), which is close to that of biological hydroxyapatite. The nanocomposite is characterized by high X-ray-induced luminescence and may be promising for adsorption immobilization of biologically active compounds. The results of the study indicate that the optimized conditions for the synthesis of nanophosphors have been found, which are potential candidates for biomedical applications, given their luminescent properties, low toxicity, and the possibility of further surface functionalization for adsorption saturation with molecules of medical interest.