Preparation and structure of calcium hydroxyapatite substituted with light rare earth ions

The present study synthesized five types of hydroxyapatite (Hap) particles containing light rare earth ions (Ln3+: La3+, Ce3+, Pr3+, Nd3+ and Sm3+) and Ca2+ ions from aqueous solutions with different Ln/(Ln + Ca) atomic ratios ([XLn]) ranging from 0 to 0.15. The crystal phases of the products and their inner and surface structures were investigated by various means. Ln3+ ions were incorporated into the CaHap crystals and formed rare earth metal–calcium hydroxyapatite (LnCaHap) solid solutions at [XLn] ≤ 0.01–0.03. A mixture of LnCaHap and LnPO4 was formed in each Ln system at [XLn] > 0.01–0.03. Ln3+ ions strongly affected the structure of the particles, although only a small quantity of Ln3+ ions was incorporated into the Hap crystals. With increasing [XLn], the prepared particles first became longer and then became smaller. The crystallinity of the particles was altered, corresponding with the variation of their size. UV–vis measurements revealed that Ce-contained Hap exhibits strong UV absorption under 400 nm.

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► LnCaHap solid solution particles were prepared using five types of light rare earth ions by a wet method.
► Ln3+ ions strongly affected the crystal phases and structures of the particles.
► Ce-contained Hap particles exhibited strong UV absorption.