Synthesis And Modulation Of Multiple Emissions From An Integrated Single-structure Based On Upconversion Nanoparticles

Rare earth doped upconversion luminescent materials is a kind of inorganic crystal materials,which can convert long wavelength,low energy near infrared light into short wavelength,high energy ultraviolet or visible light.Because the various kinds of rare earth ions have ladder-like 4f energy levels,which not only make the change of multiphoton excitation process become the reality,but also make the emission line spaning the entire visible region,providing endless possibilities for a wide range of color modulation.Compared with the traditional fluorescent dyes or quantum dots,because of the use of near-infrared excitation,the upconversion materials can give strong penetrating ability and avoid the interference of background fluorescence.In addition,the upconversion luminescence has narrow band,long life time and high light stability,which has been widely used in imaging,biological labeling,medical diagnosis,photodynamic therapy and other fields.In this dissertation,we try to build in a single nanoparticle with a variety of emission color as the core idea,explore several common upconversion materials,in order to get the output of red-green-blue color;using the core-shell structure strategy,the different luminescence centers were integrated into a single nanoparticle to realize multicolor emission;research the effect of excitation wavelength and excitation energy of the single-particle,realize controllable modulation of luminous color;reveal its application in multi-color display and biological markers in the field.The main research contents of this paper are as follows:1.We first selected three classical upconversion emission material matrix,including phosphate,oxide and fluoride.Explored the most suitable method to synthesis of upconversion nanomaterials,and discussed the morphology,structure and luminescence properties through a variety of methods.We discussesed the realization of the monochromatic output of red green blue primary colors by doping rare earth ions such as Er³⁺,Tm³⁺,Ho³⁺,and so on,which lays a foundation for the next step to realize the spectral combination of single particles.2.Using one-pot successive layer-by-layer injection method with upconversion effect Er or Tm element and downconversion Eu element to integrate luminescence in a single NaGdF₄ fluoride matrix for dual emission.First of all,Yb and Er/Tm elements were co-doped in the nucleus,and the green/blue emission of Er/Tm was observed under 980 nm near-infrared excitation,while the Eu element were co-doped in the shell,and the particles showed a red emission under 254 nm UV light excitation.At the same time,in order to prevent the quenching of the luminescence caused by the interaction between the two light-emitting units,the NaYF4 passivation layer was used to improve the luminescence efficiency.3.Single particle white-light upconversion materials have been successfully constructed using layer by layer epitaxial growth technology and red-green-blue three primary color combination strategy.By means of high-resolution transmission electron microscopy,XRD powder diffraction and other methods,it is proved that the as-synthesized white-light single particle has three layers,and the distribution and proportion of elements are consistent with the previous design.A series of comparative experiments have been designed to show that the three layer structure has a decisive effect on the tricolor output.Based on the principle of color superposition,the doping ratio of three kinds of rare earth elements was optimized to make the three colors into bright white-light.4.Because of the spectral superposition strategy with three individual rare earth ions,different light emitting units have different upconversion pathways,the output color will change with the power density of the excitation laser.We found that when the excitation power density increased from 3 to 30 W cm^-2,the single particle showed a continuous emission color evolution from green to blue to white and to red.The method of changing the excitation power density provided a new way to modulate the color of single particle.Subsequently,we successfully applied this color modulated single particle to flat-panel displays and biomarkers.