Preparation And Properties Of Rare Earth Doped Up-conversion Micro-nano Structure NaYF₄

Up-conversion mesoporous microsphere represented by NaYF₄:Yb,Er is a class of multi-functional new materials with both up-conversion fluorescent biomarkers and imaging,as well as mesoporous adsorption and slow-release drugs.It has attracted much attention because of the wide application prospect in early diagnosis and targeted synergistic therapy of tumors.However,the controlled preparation of NaYF₄up-conversion mesoporous micro-nano structure materials is still challenging.In this thesis,a green synthesis method of up-conversion mesoporous microspheres was developed by using multidentate polymers(e.g.,sodium polyacrylate)as a microreactor to control the growth of NaYF₄ nanocrystalline nuclei and induce their self-assembly.The universality of this method has also been studied.The main research content and results are as follows:NaYF₄:Yb,Er were synthesized by solid-liquid thermal decomposition and coated with SiO₂,NaYF₄:Yb,Er@SiO₂ nanocrystals were synthesized.When calcined at 700?for 3 h,the morphology of nano-particles remained,and NaYF₄ reacted with SiO₂ shell to form a new phase of Na YSiO₄.The up-conversion luminescence intensity of Na YSiO₄ exceeds that of the best known up-conversion luminescence substrate NaYF₄.When calcined at higher temperature,the morphology of nano-particles could not be maintained and agglomerated,and the nano-particles were transformed into Na Y₉Si₆O₂₆ with poor luminescence properties.Taking sodium polyacrylate(PAAS)as an example,the up-conversion mesoporous microspheres of NaYF₄ were synthesized by multidentate polymer"microreactor"method.The effect of the concentration of PAAS aqueous solution on the crystal phase and morphology of NaYF₄ was investigated.It was found that the crystal phase of NaYF₄ changed from?-phase to?-phase with the increase of the concentration of PAAS,and the"nanoparticle accumulation"of the sample first decreased and then increased.The formation mechanism of NaYF₄ up-conversion mesoporous microspheres was discussed.In this reaction system,the agglomeration of nanocrystals can be formed by reducing the polymer concentration and reducing the protection of ligands to single nanocrystals.Under the condition of high concentration of PAAS,the nanoparticles coiled together through the long carbon chain of the polymer to form mesoporous microspheres.When NH₄F was used as the fluorine source,the size of NaYF₄microspheres sample was smaller,and the specific surface area and pore volume were larger.It was found that the size of?-NaYF₄ microspheres was inversely proportional to the free F^-content at the beginning in the system of the reaction.Finally,the universality of the multidentate polymer microreactor was studied,and it was found that PAAS could also be used to synthesize other types of up-conversion porous materials,using other types of multidentate polymers as the microreactor could also enable the synthesis of NaYF₄ with functional structure.