Raman and cathodoluminescence spectroscopies of magnesium-substituted hydroxyapatite powders
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G. Pezzotti Ceramic Phaysics Laboratory & Research Institute for Nanoscience (RIN), Kyoto Institute of Technology, Kyoto 606-8585, Japan
G. Celotti, E. Landi, and A. Tampieri Institute of Science and Technology for Ceramics-National Research Council, 48018 Faenza (RA), Italy (Received 20 October 2004; accepted 19 January 2005)
Stoichiometric and magnesium-substituted synthetic hydroxyapatite (HA) powders with different Mg contents were characterized by Raman and cathodoluminescence (CL) spectroscopies. The substitution of Ca ions by Mg is presently of great interest because it may improve activity in the first stage of the bone remodeling process. In this paper, we show new evidence that CL spectroscopy has the capability to detect the presence of crystal defects, related to the presence of magnesium substituting calcium in Mg-doped HA powders. The dependence of CL spectra of stoichiometric and magnesium-doped HA powders on their chemical composition was studied, and the results are compared with Raman analysis and data previously collected by other analytical tools. All the investigated powders showed five distinct CL bands; moreover, in magnesium-doped HA, an additional band at higher energy was found. The intensity ratios between selected CL bands showed some relationships with the powder crystallinity and the estimated amount of magnesium both in the HA lattice and in the amorphous surface layer; moreover the band observed only in magnesium-substituted powders could be directly related to the amount of magnesium entered into the HA lattice. Such results can contribute to improve the knowledge of the crystallographic structure of Mg-substituted hydroxyapatite. I. INTRODUCTION
Calcium hydroxyapatite (HA) is the main inorganic phase of bone tissue. However, the HA lattice can easily incorporate a variety of both cationic and anionic elements that induce modifications in the degree of crystallinity, morphology, lattice parameters, and stability of the apatite structure. The crystallographic ability of incorporating different elements can be exploited in the preparation of synthetic materials with functional characteristics mimicking biological apatites. In fact, they are strongly nonstoichiometric and systematically contain structural imperfections and defects as well as foreign ions,1,2 which increase its structural instability. For the same reason, structural and compositional characterization of non-stoichiometric apatites can be difficult due to overlapping effects. Among substituting cations, Mg is widely studied due to its biological relevance. It has been verified that in calcified tissues, the amount of magnesium associated with the apatitic phase is higher DOI: 10.1557/JMR.2005.0132 J. Mater. Res., Vol. 20, No. 4, Apr 2005
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(about 5 mol%) at the initial stage of the bone remodelling process and decreases with increasing calcification.3 Moreover, there is growing evidence that magnesium may be an important factor in the qualitative changes of the bo
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