Synthesis And Photoluminescence Properties Of Core-Shell-Shell Structured Rare Earth Phosphate SiO₂@repo₄@SiO₂ Nanomaterials

In recent years,core-shell-shell structured rare earth nanomaterials have received much attention owing to their favorable physical and chemical properties and potential application in the fields of displays,optics,biological fluorescent labelling,and biological imaging,and so on.SiO₂ is one of the excellent candidates in fabracating core-shell materials due to its non-toxicity,low price,good biocompatibility.And the surface of SiO₂ has a large number of silanol groups which can be further functionalized.In this paper,a core-shell-shell structured SiO₂@REPO₄@SiO₂ was controllably synthesized by a bridging ligand organosilane HOOCC₆H₄N(CONH?CH₂?₃Si?OCH₂CH₃?₃?MABA-Si?to connect the SiO₂submicro-sphere by the condensation of silicon hydroxyl group,the carboxyl group to coordinate with rare earth ions,the substitution reaction of phosphate and the hydrolysis of tetraethoxysilane.The structure of the core-shell-shell structured SiO₂@REPO₄@SiO₂ was determined by infrared spectroscopy?IR?,X-ray diffraction?XRD?and X-ray photoelectron spectroscopy?XPS?.The micro-morphology of the products was investigated by scanning electron microscopy?SEM?,transmission electron microscopy?TEM?and high resolution transmission electron microscopy?HRTEM?.The photoluminescence properties of the products were measured by photoluminescence spectrum?PL?,decay curve and quantum yield.1.The SiO₂ submicro-spheres with a diameter of 200 nm were synthesized by the St?ber method,the core-shell structured SiO₂@CePO₄:Tb was synthesized by a bridging ligand organosilane MABA-Si connecting the SiO₂ submicro-sphere and the rare earth ions(95%Ce³⁺and 5%Tb³⁺),the rare earth ions react with phosphate to form rare earth phosphate on the surface of SiO₂ submicro-sphere,then their surfaces were coated with SiO₂ by the hydrolysis of tetraethoxysilane to obtain the core-shell-shell structured SiO₂@CePO₄:Tb@SiO₂.TEM images display that SiO₂@CePO₄:Tb@SiO₂ has a?25 nm outermost shell,a?4 nm intermediate shell,and a?200 nm core.HRTEM and STEM images display that SiO₂@CePO₄:Tb@SiO₂has an obvious“core-shell-shell”structure.The core-shell-shell structured SiO₂@CePO₄:Tb@SiO₂ exhibits stable photoluminescence properties in aqueous solution:its photoluminescence intensity was unquenched even after 15 days.The core-shell-shell structured SiO₂@CePO₄:Tb@SiO₂ was found to have better photoluminescence than the core-shell structured SiO₂@CePO₄:Tb.The SiO₂ shell can protect the phosphor materials from the perturbation of environment,reduce the surface defects of CePO₄:Tb and then improved its photoluminescence intensity.2.The core-shell-shell structured SiO₂@LaPO₄:Eu@SiO₂ were synthesized by a bridging ligand organosilane MABA-Si connecting the SiO₂ submicro-sphere and the rare earth ions(95%La³⁺and 5%Eu³⁺),the substitution reaction of phosphate and the hydrolysis of tetraethoxysilane.HRTEM and STEM images show that SiO₂@LaPO₄:Eu@SiO₂ has obvious“core-shell-shell”structures.TEM and HRTEM images clearly display that the intermediate shell of the core-shell-shell structured SiO₂@LaPO₄:Eu@SiO₂ was composed by LaPO₄:Eu nanoparticles with a size of 15nm³4 nm,5 nm⁷ nm and⁴ nm.The size of the intermediate shell LaPO₄:Eu nanoparticles was changed by altering the condition of the hydrolysis and condensation condition of MABA-Si and the substitution reaction condition of phosphate.When the MABA-Si grafting on the surface of SiO₂,the larger thickness the MABA-Si is,the larger the size of the LaPO₄:Eu nanoparticles is.The photoluminescencepropertiesofthecore-shell-shellstructured SiO₂@LaPO₄:Eu@SiO₂ were studied for solid state and the aqueous solution.It was found that the positions of the strongest characteristic emission peaks of Eu³⁺ions were different with different sizes of the intermediate shell LaPO₄:Eu nanoparticles.According to the Judd-Ofelt?J-O?theory,when the size of the intermediate shell LaPO₄:Eu nanoparticles is 15 nm³4 nm,5 nm⁷ nm and⁴ nm,the Judd-ofelt parameter?₂?optical transition intensity parameter?is 1.20×10^-20,1.80×10^-20 and2.30×10^-20,respectively.The J-O parameter?₂ increase gradually,indicating that the symmetry of Eu³⁺in LaPO₄ matrix decreases gradually.Simultaneously,the photoluminescence properties of core-shell-shell structured SiO₂@LaPO₄:Eu@SiO₂submicro-spheres in aqueous solution were studied:its photoluminescence intensity was stable in aqueous solution.3.This paper,with the SiO₂ as the core material,the low-cost preparation of rare earth orthophosphates luminescent materials could be achieved,the SiO₂ as the shell material can protect the phosphor materials from the perturbation of environment to improve its photoluminescence intensity,combine with biomolecules and improve its biocompatibility.The interaction characteristics of the core-shell-shell structured SiO₂@LaPO₄:Eu@SiO₂ with bovine serum albumin?BSA?were studied by the spectroscopic technique.The photoluminescence spectrum displays that the core-shell-shell structured SiO₂@LaPO₄:Eu@SiO₂ can effectively quench the intrinsic fluorescence of BSA through a static quenching mode.This indicated that core-shell-shell structured SiO₂@LaPO₄:Eu@SiO₂ with BSA formed the SiO₂@LaPO₄:Eu@SiO₂-BSA complex.The synchronous photoluminescence spectroscopy indicated that the core-shell-shell structured SiO₂@LaPO₄:Eu@SiO₂have a quenching effect on the tryptophan and tyrosine residues of bovine serum albumin.The binding site of the SiO₂@LaPO₄:Eu@SiO₂ and BSA is closer to tryptophan.The results provide a reference for the application of the core-shell-shell structured SiO₂@LaPO₄:Eu@SiO₂ in biomolecules labeling field.