Effect Of Anions In Calcium Phosphate Matrix On The Fluorescence Properties Of Eu³⁺ And Its Application

Calcium phosphate（CaP） is the main inorganic component of human hard tissue.CaP crystals such as hydroxyapatite have unique crystal structures that accept doping and substitution of other ions.Rare earth ions（RE）such as Eu³⁺and Tb³⁺doped CaP can be used as luminescent materials.The fluorescence characteristics of RE will be strongly affected by the anions in the CaP matrix.Therefore,it is necessary to discuss the influence of the anions in the CaP matrix on RE fluorescence and its mechanism,so as to optimize its fluorescence performance.In this paper,europium(Eu³⁺)was selected as the doped ion to study the influence of hydroxyl fluoride（F^-）substitution and phosphate ion(PO₄^3-)concentration on the luminescence performance of Eu³⁺.Furthermore,based on the linear relationship between Eu³⁺fluorescence intensity relative ratio and PO₄^3-concentration,the quantitative detection of inorganic phosphorus based on Eu³⁺fluorescence was studied.Firstly,Eu³⁺doped hydroxyapatite(（Ca,Eu）₅（PO₄）₃（OH）_1-xF_x),Eu:F_xH_1-xAP)with different hydroxy-fluorine substitution rates were prepared by hydrothermal method.The relationship between luminescence intensity of Eu³⁺and hydroxy-fluorine substitution rate was discussed.The effects of hydroxy-fluorine substitution on the phase composition,crystallinity,grain size and morphology of Eu:F_xH_1-xAP nanomaterials and the change of fluorescence intensity were analyzed.The results showed that with the increase of hydroxy-fluorine substitution rate,Eu:F_xH_1-xAP was still an apatite structure;the grain size decreased;the rod-like structure gratually shortened in the length direction;the fluorescence life and quantum yield increased;and the fluorescence intensity gradually increased.The increase ratio of fuorescence intensity relative ratio shows a linear increase relationship with the increase of fluorine substitution rate.Secondly,based on the polyacrylic acid（PAA）complex-coprecipitation method,PAA-Ca²⁺(Eu³⁺)complex was used as a precursor to regulate the precipitation process of Ca²⁺(Eu³⁺)and PO₄^3-.The effect of PO₄^3-concentration on the fluorescence performance of Eu³⁺was studied.The results showed that the PAA-Ca²⁺(Eu³⁺)complex has a particles size between 2-3 nm and has good water solubility and stability.The PAA-Ca²⁺(Eu³⁺)complex shows a good fluorescence response to the concentration of PO₄^3-ion.Within a certain PO₄^3-concentration interval,the fluorescence intensity increase rate showed a linear increasing trend with the increase of PO₄^3-concentration.Finally,based on the influence of the concentration of PO43-ion on the fluorescence intensity of Eu³⁺ in the precursor of PAA-Ca²⁺(Eu³⁺)complex,the quantitative detection method of inorganic phosphorus based on Eu³⁺fluorescence was established,and the application research on the quantitative detection of inorganic phosphorus was carried out.In addition,the linear detection range and reliable fluorescence interval of the fluorescence intensity increase rate were determined.The results show that the Eu/（Ca+Eu）molar ratio in the PAA-Ca²⁺(Eu³⁺)complex precursor has an impact on the quantitative detection range of PO₄^3-.The increase in the molar ratio could broaden the quantitative detection range.When the molar ratio was 5%,the linear relationship between fluorescence intensity growth rate of Eu³⁺and concentration of PO₄^3-was y=0.897x-0.27,R²=0.99,and the linear detection range was 0.25～3.75m M;when the molar ratio was 5%,the linear relationship between fluorescence intensity growth rate of Eu³⁺and concentration of PO₄^3-was y=0.601x-0.098,R²=0.99,and the linear detection range was 0.25～7.5mM.