| Rare earth materials have excellent optical properties due to their abundant 4f energy level structures,which make them widely used in petrochemical,glass ceramics,biomedical imaging and many other fields.Rare earth fluoride is one of the most commonly used upconversion matrix materials because of its low phonon energy and stable chemical properties.Rare earth upconversion(UC)luminescent materials have many advantages,such as narrow band gap emission,large anti-stokes shift,high stability and low toxicity.In addition,the near-infrared light as excitation light source can effectively avoid biological self-fluorescence interference and improve the detection sensitivity.Therefore,UC luminescent materials can be widely used in biomarkers,cell imaging,biosensor and other aspects.However,the low fluorescence efficiency of UC limits its further development.Based on the above research background and application requirements,this thesis mainly focuses on the luminescence enhancement of rare earth fluoride UC materials,biological imaging applications and the preliminary exploration of high-efficiency X-ray-excited luminescent materials.The main innovations include:UV-blue upconversion emissions of Tm3+ can be significantly enhanced through Fe3+ doping in the ultra-small ?-NaYbF4 host materials;By constructing the PEG-?-NaYbF4:Fe,Er,Gd dual-mode nano-fluorescent probe,improved the contrast of in vivo/vitro computed tomography(CT)imaging;The X-ray-excited ?-NaLuF4:Tb/Eu nanocrystals were synthesized and the energy transfer mechanism between Tb3+ and Eu3+ was explored.The specific research results are shown as follows:(1)Ultra-small,monodisperse,and highly uniform p-NaYbF4:0.5%Tm,X%Fe upconversion nanoparticles(UCNPs)were obtained by using the solvothermal route.Under 980 nm excitation,UV-blue emissions enhancement of Tm3+were achieved via Fe3+ doping.Remarkably,5 mol%was the optimum Fe3+ doping concentration for enhanced UV UC luminescence(UCL).Fluorescence lifetime decay data from the 1I6 energy level of Tm3+ further verified UC emission spectrum variation tendency with the increase of FeUUdoping concentration.The phenomenon of luminescence enhancement was theoretically explained by building an energy transfer system between Yb3+-Fe3+dimer and Tm3+.(2)Ultra-small(?10 nm)?-NaYbF4:5%Fe,2%Er,X%Gd(X=5,10,15,20 mol%)UCNPs were synthesized by using a solvothermal approach.The surface polyethylene glycol(PEG)functionalization of the as-prepared ?-NaYbF4:5%Fe,2%Er,X%Gd UCNPs was carried out by using a modified ligand-exchange strategy.The Gd3+doping is beneficial to regulate the grain size,and Fe3+ doping can selectively enhance the red emission of Er3+ to improve the tissue penetration depth.In this work,it was proved that the UCNPs has good UCL performance by confocal luminescence imaging in vitro at first.Then,the UCNPs was applied to computed tomography(CT)imaging by utilizing the high absorption capacity on X-ray of Yb element and the enhanced effect on CT imaging of Fe/Gd codoping.Thirdly,according to the results of MTT test,which verified the UCNPs had a low biological toxicity.In summary,the experimental results showed that PEG-?-NaYbF4:5%Fe,2%Er,10%Gd UCNPs can effectively and selectively accumulate in the tumor site of mice,and obvious CT enhancement effect was presented.So this material can be used as a dual-mode PL/CT biological probe.(3)Monodisperse,uniform ?-NaLuF4:X%Tb(X=3,6,9,12,15,20,25 mol%),?-NaLuF4:X%Eu(X=5,10,15,20 mol%)and ?-NaLuF4:15%Tb,X%Eu(X=5,10,15,20 mol%)nanocrystals have been successfully synthesized by a solvothermal method.Under X-ray excitation,Tb3Ldoping concentration was optimized at first,and then change the TbIU/Eu3udoping ratio,achieving the color regulation of?-NaLuF4:Tb,Eu nanocrystal.The phenomenon of the color transition was further explained by building an energy transfer system between 5D4(Tb3+)and SD1(Eu3+)under X-ray excitation.Due to the excellent optical properties of ?-NaLuF4:Tb,Eu and the energy matching of Tb3+/Eu3+,it is expected to be a new type of material with dual luminescence center/dual photosensitizer for photodynamic therapy(PDT)under X-ray excitation. |
PDF Full Text Request