Study On Optical Properties Of Rare Earth Fluoride (NaREF₄:Ln³⁺) And Its Bioimaging Application

Rare earth luminescence materials had attracted the great attention in the biomedicine field,owing to its unique 4f electronic layer structure and luminescence properties.Rare earth fluorides were widely studied due to its low phonon energy and stable chemistry properties.In order to achieve the application demand in biomedicine field,the researchers devoted to explore and study the materials which own uniform size（～30 nm）,high quantum yield,and long luminescence lifetime,expecting to apply the new materials and technologies in in vivo/vitor imaging or early therapy for clinic cancer,and realizing the early diagnosis or precise treatment for human lesion.Based on the needs of application,this thesis presented enhanced upconversion luminescence（UCL）of rare earth fluorides and the development of high-efficiency X-ray-excited materials and its biological application.The main research contents shown as below:（1）Uniform（-30 nm）,monodisperse β-NaYF₄:18%Yb,0.5%Tm,X%Zn（X = 0,1,2,3,4,5 mol%）nanocrystals had been obtained via a solvothermal routine,which achieved the blue emission enhancement of Tm³⁺ for the first time at nanoscale.UCL spectra acquired at room temperature illustrated the specific enhancement for blue emission of Tm³⁺ doped with different concentrations of Zn2+,and the optimum Zn2+content was 1%.Subsequently,the luminescence decay time of 1G4 energy level for Tm³⁺ further proved Zn2+ doping could enhance the UC blue emission（475 nm）of Tm³⁺ particularly.Meantime,it had no effect on the three-photon UC process of the emission for 1G4 energy level.At last,the mechanisms of the enhanced UC blue emission were explained through the changing of crystal lattice environment for activator.（2）Monodisperse,uniform（-30 nm）β-NaLuF₄:18%Yb,0.5%Tm,X%Fe（X = 0,2.5,5,6 7.5,10 mol%）nanocrystals had been successfully synthesized by a solvothermal method,and then studied its luminescence properties and in vivo/vitor computed tomographic（CT）imaging.UCL spectra and the dynamic lifetime characterizations demonstrated the ultraviolet emissions of Tm³⁺ enhanced largely with effective Fe³⁺ doping.Then,the UCL mechanisms of Yb³⁺-Tm³⁺-Fe³⁺ system were discussed,and the main reason for enhanced ultraviolet emission was attribute to the back-energy transfer between Yb³⁺-Fe³⁺dimer and Tm³⁺.Lastly,based on the specific bioimaging properties of the Lu element,selecting the nanocrystals with best luminescence properties to carry out functional modification by using 2-Aminoethylphosphonic acid（AEP）and in vivo/vitor CT imaging.The experiment results indicated the surface modified nanocrystals own low bio-toxicity which benefits for bioimaging.When the nanocrystals were used for in vitor CT imaging,its imaging effect was obviously better than the commercial CT contrast agent iopromide;it also had distinct enhancement of targeting tumor location when the nanocrystals were used for in vivo CT imaging.（3）Ultra-small size（10 nm）,monodisperse and uniform β-NaGdF₄:X%Eu（X = 1,5,10,15,20,25 mol%）nanocrystals were synthesized using a solvothermal approach,and applied in X-ray luminescence computed tomographic（XLCT）imaging in vivo/vitor.The results demonstrated that the Eu³⁺ contents did not change the size and morphology of(3-NaGdF₄ nanocrystals,while had obvious effect on the luminescence properties under X-ray excited.And then,β-NaGdF₄:X%Eu nanocrystals were modified by using polyacrylic acid（PAA）through a ligand exchange method,which could be used for in vivo/vitor XLCT imaging.The ultra-small,X-ray-excited,surface modified PAA-NaGdF₄:15%Eu nanocrystals with excellent biocompatibility and stability,which compared with bulk material Y₂O₃:15%Eu,exhibited the accurate location performance.