Preparation,Structure And Properties Of Erbium-Doped Hydroxyapatite

Hydroxyapatite（HAP）is the main inorganic substance in human bones and teeth.It has good biocompatibility,bioactivity and degradability.However,natural HAP minerals are complex in composition and are not suitable for some high-end applications.HAP pure minerals were prepared and doped with functional components to develop HAP mineral materials into multifunctional composite mineral materials on the basis of maintaining the original excellent properties.In this paper,erbium-doped hydroxyapatite（Er-HAP）particles were prepared by co-precipitation method,and several variables such as p H adjuster,p H value,reaction temperature,reaction time and calcination conditions were compared to optimize the preparation process of Er-HAP.The crystal structure,surface chemical composition and fluorescence properties of HAP were characterized by Materials Studio simulation with X-ray powder diffraction,scanning electron microscopy-energy spectroscopy,X-ray photoelectron spectroscopy,elemental analysis and fluorescence spectroscopy.The results showed that the Er-HAP crystals were optimally prepared under the experimental conditions of erbium nitrate as the erbium source,saturated Na OH solution to adjust the reaction p H value to 12.21,heating at 120℃for 10 min,aging for 12 h,and calcination at 800℃for 2 h.In addition,the OH-form in the reaction solution was found to be the best.In addition,the OH-concentration in the reaction solution could effectively control the growth of Er-HAP in the c-axis direction,and the Er-HAP model was constructed by Materials Studio to identify the preferentially substituted calcium ion sites in HAP.Rare-earth ions have good photoluminescence properties,and the superior combination of both rare-earth ions and HAP is of great research value.The photoluminescence（PL）test revealed that the Er-HAP particles had efficient luminescence performance after being excited at about 340 nm,showing four luminescence bands in violet,blue and green,corresponding to four leaps of ⁴F_3/2→⁴I_15/2,⁴F_5/2→⁴I_15/2,⁴F_7/2→⁴I_15/2 and ⁴S_3/2→⁴I_15/2,respectively.The fluorescence lifetime and absorbance of Er-HAP particles were enhanced with the increase of erbium ion doping concentration,indicating that Er-HAP particles have the potential to become a bioimaging mineral material.Based on the good biocompatibility of HAP mineral materials,Er-HAP particles were immersed in simulated body fluids（SBF）of different p H values for 3 and 7 days.The results showed that Ca²⁺,PO₄^3-and OH^-were more easily deposited in SBF at p H 7.A mineralized layer was formed on the surface of the soaked Er-HAP minerals,attached to the original surface structure in irregular flakes that interpenetrated in a reticular pattern.In addition,comparing the mineralization rate of 1%Er-HAP and 9%Er-HAP,it was found that the amount of erbium ion doping had an effect on the mineralization rate.With the increase of erbium doping amount,the mineralization rate and osteogenic properties of Er-HAP surface were significantly reduced.With the controlled doping amount,Er-HAP has the potential to become a mineral material with good luminescence and both biocompatibility.This study provides a basis for the potential application of ER-HAP particles in the field of biological imaging,and also provides a reference for the study of the occurrence state of erbium ion embedded in bone and hydroxyapatite.