Preparation And Properties Of Rare Earth Fluoride Upconversion Nano Luminescent Materials

Hydrophilic NaYF₄ upconversion mesoporous submicron materials are becoming a hot spot for their great potential in the early diagnosis and synergistic treatment of cancer.However,the current complex design and inefficient preparation methods result in too high cost to become commercial products to benefit society.In this thesis,hydrothermal/solvothermal methods were utilized to fabricate upconversion phosphors suitable for application in biomedical.Strategies to tune the morphologies and upconversion luminescence properties were studied as well.The main research content and results are as follows:（1）Hydrophilic NaYF₄:Yb,Er upconversion nanomaterials were fabricated through a one pot solvothermal method.By tuning the effective carboxyl concentration which coordinated with rare earth ions,the morphology and luminescence properties can be tuned through tuning the adding amount of NaOH or citric acid.Then the growth and phase inversion process of NaYF₄ was adjusted.As a result,the particle sizes,morphologies,crystalline phases and the luminescence properties were tuned.Study also found that the particle size can be reduced through adding CTAB,DTAB or sodium oleate as the second surfactant.This chapter provides an example of control synthesis of NaYF₄:Yb,Er upconversion nanoparticles as well as the relationship between the surface defects and upconversion properties.（2）A green and efficient method was developed to fabricate mesoporous NaYF₄:Yb,Er upconversion microspheres through utilizing high concentration of PAAS aqueous as the solvent.The threshold concentration was 1.3 mol/L,which was 40 times as reported in the literatures.The formation mechanism was polymerase chain induced“ Oriented Attachment”:Directed by long carbon chain of PAAS,the primary nanoparticles assembled to form mesoporous microspheres.“Microbubble template model” was proposed according to the differences between the products utilizing NaF and NH4 F respectively.At last,mesoporous CaF₂:Yb,Er upconversion nanoospheres were obtained,which illustrated the universality of this method.（3）La³⁺ doped NaYF₄:Yb,Er upconversion microprisms were fabricated through hydrothermal method.With increasing La³⁺ doping concentration,the length to diameter ratio decreased and the upconversion luminescence was enhanced.And when the La³⁺ doping concentration reached 20 mol%,the luminescence intensity was the strongest.La³⁺ codopinglowered the symmetry of the rare earth ion local crystal field to enhance the upconversion luminescence.Good linear relationship was found by a linear fitting between the nature logarithm of the upconversion luminescence intensity ln（I）and the cooresponding cell parameters.