Study On The Controllable Preparation And Rare Earth Doped Luminescence Of Hydroxyapatite Nanocrystals In Inorganic Environment

Hydroxyapatite（HAp）has drawn growing attention over decades for use in the fields of materials science and biomedical engineering and more recently in nanotechnology owing to its excellent bioactivity and biocompatibility.In view of above excellent properties,the HAp nanomaterials also are applied to drug delivery,biological probes,and bioimaging by tailoring the size and morphology of the nanoparticles for each application.It is of great importance to control the size and morphology of nanostructured HAp material while minimizing or avoiding any contaminants that can adversely affect biocompatibility and cause toxicity or inflammation.Based upon classical methods for nanoparticle synthesis,a series of methods are emerging to achieve the nano-HAp size and morphology variations.For example,hexadecyl trimethylammonium bromide（CTAB）,glycol,oleic acid and octadecylamine are usually used in the solvent during preparation to control the size distribution of the HAp particles and achieve various shapes of HAp particles.However,it is believed that organic additives will introduce toxic substances that can damage the bioactivity and biocompatibility of HAp.Removal of organic components may require high treatment temperatures that can adversely affect the morphology of the nanostructured HAp particles.Therefore,it is imperative to develop a surfactant-free synthetic method at relatively low temperatures for controlling the size and shape of HAp nanoparticles.To our best knowledge,the method for controlling the sizes of HAp nanoparticles without organic additives has been scarcely reported.In this study,the size tunable HAp nanoparticles were successfully prepared via surfactant-free hydrothermal method assistedwithcoprecipitation process,whileretainingbioactivityandthe biocompatibility of HAp.In the further research,the growth process of HAp nanocrystals and the influence mechanism of OH^-on the growth of HAp crystals were discussed.The results show that the average size of HAp crystallites could be controlled from 1.5μm to 50nm by controlling the synthesis conditions of HAp,and the morphology changes from nanobelts to nanoparticles.In addition,the concentration of OH^-can effectively control the crystal space growth of HAp along the direction of the C-axis,which could be explained by the theoretical model of anionic coordination po1yhedron growth units.It is also shown that,in further advancing the potential use of nano-HAp in medical applications,the HAp nanorods emit bright green and red-orange light after doping with terbium and europium,respectively,upon excitation with blue light.Finally,the PL spectra of HAp:Tb³⁺with different grain sizes are analyzed,and the result shows that the luminescence intensity of the sample was influenced by multiple factors such as grain size,crystallinity,and doping amount of RE.