Synthesis And Assembly Of High-quality Rare-earth-doped Upconversion Nanoparticles

Rare-earth doped nanoparticles, with a combination of nano-size and specialrare-earth characteristics, have been widely used in various fields such as optics,electrics and magnetics in recent decades. One of the rare-earth doped upconversionluminescent nanoparticles have become the focus since they have special luminescentproperties which is to emit a high-energy photon with absorbing tow or morelow-energy excitation photons. As a kind of upconversion luminescent particles whichis the most stable, most controllable in shape and pattern and has the least defect andmost intensive luminescence, the lanthanides doped NaYF4is applied in lasers,anti-counterfeit labels, fingerprint acquisition and so on, especially several applicationsin biomedical science these years. However, the previous synthesis routines are notsuitable for mass production because of high-energy consumption, high cost andpoisonous by-product. So a new synthesis method which is more environmental friendlywith lower energy consumption and cost is in urgent need. On the other hand, this kind biomedical science, which means the particles synthesized in organic phase should betransferred in to aqueous phase. The previous method is complicated since a newcondition should be made with every single function group. Thus it is necessary to finda simple, convenient and universal method for organic-to-aqueous phase transportation.While simply upconversion is not enough for imaging, a kind of composite luminescentparticles is needed for various colors or luminescent controllable composites.In Chapter II, on the premise of low energy consumption and low cost, we havesynthesized upconversion luminescent, uniform and hexagonal NaYF₄:Yb³⁺,Er³⁺(Tm³⁺)particles using oleic acid as the ligand and liquid paraffin as solvent at relatively lowtemperature (280℃). Based on this method, the crystals phase can be changed fromcubic to hexagonal crystal. Particles sized from20nm to150nm can be prepared viacontrol of heat duration; and the shape can be ball, ellipse,plate,cubic through thechange of ligand and solvent; while the color of the luminescence can be tuned bydoping of different lanthanide. We studied the impacts of particle patterns, sizes, andcrystal types, the intensity of upconversion luminescence and color change throughrigid control of reaction condition, which is totally controllable. Finally we tunedupconversion luminescence color via doping of transition metal elements. This realizesthe excitation and emission ranging from red light to near-infrared, which make a easierimaging inside biological body. From the experiment above, we have lowered cost andenergy consumption for mass production in "green" and environment protection,providing promising application.In chapter III, we use common small molecule surfactants and particle claddingoleic acid ligand to build double-layer structure through hydrophobic-hydrophobicinteraction and outward hydrophilic end to transport particles from organic phase toaqueous phase. The aqueous phase particles showed good dispersion and upconversionluminescence. This method was easy to operate, and universal for ion-, anion-, and non-ionic surfactant. silicification on the surface and polymerization can be carried outwith different properties with the change of surfactant, forming SiO2or PPy core-shellstructure. Then we can obtain nanoparticles converted on independent dispersed ordifferent sized super structure assembly using microemulsion droplets template viachange of concentration of surfactant. Also, the size of super structure assembly canchange from100nm to500nm in different concentration of surfactant. Thesuperstructure assemblies can be well dispersed in water, and the luminescence intensityof upconversion assembly NaYF₄:Yb³⁺, Er³⁺(Tm³⁺) is1.5times as much as those ofsingle dispersed ones. Finally we chose amphipathic triblock copolymersF127(PEO-b-PPO-b-PEO) to transport different sized upconversion nanopartiles fromorganic phase to aqueous phase. The transported NaYF₄:Yb³⁺, Er³⁺(Tm³⁺) nanoparticleswere applied in biological labeling and imaging. Upconversion nanoparticles modifiedwith F127showed good biological stability and luminescence intensity. Compared withthose small surfactant, F127is almost non-toxic to organism. Our research has providednew idea for applications of upconversion nanoparticles in biological field.In chapter IV, we first use noble metal nanoparticles interaction between Au andNaYF₄:Yb³⁺,Er³⁺(Tm³⁺) nanoparticles to control the optical proterties ofNaYF₄:Yb³⁺,Er³⁺(Tm³⁺) nanoparticles. In the experiment, we preparedNaYF₄:Yb³⁺,Er³⁺(Tm³⁺) and Au composite via (1) host-guest interaction betweencyclodextrin and NaYF₄:Yb³⁺,Er³⁺(Tm³⁺) surface oleic acid;(2) microemulsion dropletstemplate;(3) insitu synthesis of nanoparticles. The three composite can be welldispersed in water. The study of the spectrum data showed that the relative intensity ofemmisiton peaks of NaYF₄:Yb³⁺,Er³⁺(Tm³⁺) nanoparticles have changed a lot due tointroduction of Au particles. Then we use mercaptoacetic acid stabled CdTe QDs totransport NaYF₄:Yb³⁺,Er³⁺(Tm³⁺) nanoparticles from organic phase to aqueous phase,obtaining CdTe modified NaYF₄:Yb³⁺,Er³⁺(Tm³⁺) nanoparticles in different size. Duringthe study of the optical properties of this composite, we have found that under excitation of980nm near infrared, energy transfer occurred between NaYF₄:Yb³⁺, Er³⁺(Tm³⁺)nanoparticles and CdTe QDs. The specific wavelength emmision of NaYF₄:Yb³⁺,Er³⁺(Tm³⁺) nanoparticles was effectively transferred to the adsorption band of CdTeQDs, thus leading to the emission of CdTe QDs and turning of the intensity of emissionpeaks among NaYF₄:Yb³⁺,Er³⁺(Tm³⁺) nanoparticles. The preparation of multifunctionalcomposite optical material can provide wider application in biological detection andlabeling.