Preparation,Photoluminescent Properties,and Applications Of Lanthanide Doped NaYF₄

Recently,high-quality lanthanide doped rare-earth fluorides nanomaterials/micromaterials have aroused considerable attention in the forefront of materials science field,owing to their mature preparation methods,and outstanding upconversion and downshifting luminescent properties.Lanthanide-doped NaReF4-type ternary rare earth fluorides exhibit a full-spectrum range emission including ultraviolet(UV),visible,near infrared(NIR),and mid infrared(MIR)under appropriate excitation condition.Compared with lanthanide chelates,quantum dots(QDs),and organic dye molecules,lanthanide-doped ternary rare-earth fluorides hold all the advantages of a large Stokes shift,sharp emission band,long life time,high photochemical stability,high emission intensity,and low toxicity,it is readily to find applications in the fields of biological fluorescent labeling,cell imaging,three-dimensional display,laser,anti-counterfeit labels and photodynamic therapy.Althoughlanthanide doped ternary rare-earth fluorides hold attractive prospects,there are still many basic problems need to be solved.In this thesis,a series of lanthanide-activated nanometerials and micromaterials were prepared by hydrothermal method,solvothermal method and coprecipitation methodand the spectroscopic properties of the lanthanide-activated nanometerials and micromaterials were systematically studied.In the second chapter,the NaYF4 microrods were prepared by hydrothermal method.The propagation mode of the upconvertion emission light in the microrod was studied creatively and the optical waveguide performance was studied systematically.In the third chapter,a series of lanthanide ion-activated nanorods which were sensitized by a single cerium ion were successfully synthesized.The energy transfer process was studied by steady-state and transient spectroscopy.In the fourth chapter,NaYF4:Ce@NaYF4:Tb core-shell nanoparticles were prepared by coprecipitation method.Through study of their steady-state and transient spectra before and after the heat treatment,we revealed the structural integrity of NaYF4:Ce(20%)@NaYF4:Tb(20%)core-shell nanoparticles and their thermal stability.In the fifth chapter,we prepared NaYF4@NaYbF4:Ho(1%)@NaYF4 core-shell-shell nanoparticles by coprecipitation method,and presented a study of amplifying excitation power-sensitivity of upconversion in Ho3+ ions through the use of a NaYbF4 host.Mechanistic investigation revealed that the sensitive response of(?)Ho3+ upconversion to excitation power stems from maximal use of the incident energy enabled by concentrated Yb3+ sensitizers.The above research is of great significance for deep understanding and application of lanthanide-doped rare earth fluorides.The main contents of this thesis are as follows:(1)NaYF4:Yb/Er(10/1%)microrods and microtubes were prepared by EDTA-assisted hydrothermal method and sodium citrate assisted hydrothermal rmethod.Owing to the large morphology of microrods and microtubes that is beyond the diffraction limit,we can directly characterize the NaYF4:Yb/Er microrods and microtubes through optical microscopy.NaYF4:Yb/Er microrods showed the characteristic green emission,in the medium of air.Direct excitation of the emission of light can be transmitted along the longitudinal axis without the need for special alignment of the NIR irradiation.NaYF4:Yb/Er hollow nanotubes can produce a stronger optical waveguide than that of a solid microrod,optical analysis of a single microtube illustrated a stronger effect of guided emission in comparison with the solid microrod.The observation attributed to airs inside the tubes that lead to a tighter confinement of photons.Due to the good penetration of near infrared lasers and the high thermal stability and optical stability of NaYF4,this study is expected to be used in biological tissue imaging and optical sensing applications.(2)The lanthanide-doped NaYF4 nanorods were prepared by the oleic acid assisted-hydrothermial method.When the concentration of Eu3+was fixed at 0.2%,the Eu3+ held the strongest intensity emission.The energy transfer between Ce3+?Gd3+?Eu3+ was found to be related to medium of Gd3+,and there was no direct energy transfer between Ce3+ and Eu3+ without the energy transfer intermediate Gd3+.The energy transfer between Gd3+?Gd3+?Eu3+ was confirmed by the transient spectrum,where the Gd3+ lifetime is gradually reduced,conflrming the energy transfer process of Gd3+?Eu3+.With further increasing concentration of Eu3+,the rising edge of decay curves tunes from a gentle slope into a sharp fast-rising slope with increasing Eu3+ dopant concentration,which was used to describe the energy migration time from Ce3+ to Eu3+.The energy transfer can also be carried out by substituting Eu3+ ions by Tb3+,Sm3+,Dy3+ and Nd3+ ions,and the energy transfer process of Ce3+?Gd3+?Ln3+(Ln3+ = Tb3+,Sm3+,Dy3+,Nd3+)occurred.In particular,the energy transfer among Ce3+-Gd3+?Nd3+ were able to convert ultraviolet energy into near-infrared emission,and realize UV-near-infrared spectral modulation.(3)We characterize the as-synthesized NaYF4 core-shell nanoparticles by spectral respoVse between Ceu,and Tb3+ ions.It was demonstrated that the synthesized nanoparticles have perfect hierarchical structure and there was no diffusion between core and shell layers,but high temperature heat treatment would destroy the structure of nanoparticles.At high temperature above 450 0C,the original spherical core-shell structure was completely destroyed,thus Ce3+ ions and Tb3+ ions could diffuse across the core-shell interface.The potential applications of NaGdF4:Ce@NaGdF4:Eu/Tb multicolor core-shell nanoparticles in the field of security were described.The biotin-modified NaGdF4:Ce and NaGdF4:Eu nanoparticles were readily to be used for the quantitative detection of avidin by the specific binding between biotin and avidin.(4)We prepared NaYF4@NaYbF4:Ho(1%)@NaYF4 core-shell-shell structured nanoparticles by coprecipitation method.The emitted color of NaYF4@ NaYbF4:Ho(1%)@NaYF4 core-shell-shell structured nanoparticles could be changed with the excitation power.Mechanistic investigation revealed that the sensitive response of Ho3+upconversion to excitation power stems from maximal use of the incident energyenabled by concentrated Yb3+ sensitizers.This allows us to sensitively tune the red-to-green emission intensity ratio from by increasing the excitation power.Our results highlighted that the excitation-power sensitive upconversion emission can be exploited to experimentally visualize electromagnetic hotspots.Moreover,the "power-discoloration" properties of NaYF4@NaYbF4:Er(2%)@NaYF4 nanoparticles might disappear either by changing the species,doping concentration of the activated ions or by changing the kind of matrix materials.When the NaYF4@NaYbF4:Ho(1%)@NaYF4 nanoparticles were dispersed on the Au nanoarray,the plasma resonance enhancement effect of the gold nanoparticles on the upconvertion nanoparticles was visualized for the first time.