Zubar O. Synthesis and luminescence properties of calcium phosphates doped with lanthanides

The thesis is devoted to study of the relationship between the synthesis conditions, crystal structure and luminescence properties of lanthanide doped NaCaPO4 and Ca10(PO4)6(OH)2, the optimization of chemical composition and the preparative conditions of functional materials based on them. A method for obtaining functional materials based on the NaCaPO4 is developed. It implies thermolysis of the hybrid crystal-amorphous precursor containing Ca1-хNaхHPO4·nH2O (n= 0-2) as a crystalline phase. The advantage of this method is the low temperature of the NaCaPO4 formation (450°C). It is shown that the use as a precursor of Ca1-хNaхHPO4·nH2O allows to improve the particle size distribution of NaCaPO4: Eu2+ - a promising phosphor for light-emitting diodes. Even at relatively high temperature of the annealing (950°C), a luminescent material with particles' size of 1-5 microns was obtained. Based on the results of luminescence spectroscopy it is shown that Eu2+ ions occupy in NaCaPO4 predominantly positions of alkaline earth metal. The electronic structure of NaCaPO4 is mainly determined by the isolated phosphate groups PO4. The effect of synthesis conditions and Ln3+ (Eu3+, Се3+)-concentration on the distribution of lanthanide ions on Ca-positions in the structure of Ca10(PO4)6(OH)2 was studied. It was found that at relatively low concentrations (<<1 at.%) Ln3+ ions occupy mainly the Ca(I) positions. With increasing concentration of lanthanide ions their fraction in the Ca(II) position increases significantly. The influence of synthesis conditions on the distribution of the lanthanide ions on the calcium positions in Ca10(PO4)6(OH)2 is complex and determined by the processes of formation and interaction of different defects. Key words: calcium phosphates, hydroxyapatite, low-temperature synthesis, luminescence, electronic structure.