The rare earth elements have excellent characteristics in optics,electricity and magnetics owing to their own special 4f electrical configuration.In recent years,enormous researches and attentions have been paid to the lanthanide-doped fluoride upconverting luminescent materials because they have low phonon energies,long excited-state lifetimes,low toxicity,narrow emission bandwidth and other comprehensive advantages,which results in the widespread application domains of the materials,including 3D display,solid-state laser,solar cells,biological imaging and biomarkers,optical storage,anti-counterfeit printing and so on.For up-conversion luminescent materials,the matrix material,a main body of the matrix materials,served as a nonluminous energy-level but can provide a suitable crystal field for the luminescence center.In the trivalent rare earth ions,Y3+,La3+,Lu3+,etc.are suitable as a host material because they lack of electrons for their 4f energy level or are fully-filled with the electrons for the 4f sublayer,and exhibit optical inertia since they have a closed shell structure.Furthermore,upconversion matrix materials also require low phonon energy,high chemical stability and mechanical strength.In this treatise,LiYF4?NaYF4?KYF4 were chosen as the matrix materials,Yb3+ and Er3+ as the sensitizer and activator respectively.Controlled synthesis of crystal forms,sizes,and morphologies of LiYF4,NaYF4,KYF4 nanmaterials were realized by adjusting the ratio of MF/RE?LiF,Na F,KF?,reaction time,reaction temperature,etc.,and the effect of the above conditions on their luminescence properties was explored.The specific findings are as follows:?1?Preparation of rare earth trifluoroacetate precursors by hydrothermal synthesis for the first time?2?Precise control of sizes of ?-NaYF4:20%Yb3+/2%Er3+ nanoparticles?27-33nm?was achieved in the high-boiling organic solvents?oleic acid,octadecene?via thermal decomposition method,and the effect of Na F/RE ratio,reaction temperature,and reaction time on the mechanism of nucleation and growth of NaYF4:20%Yb3+/2%Er3+ nanomaterials was discussed.It is further concluded that the following processes are mainly involved in the growth of NaYF4:20%Yb3+/2%Er3+ nanomaterials.?1?Nucleation,?2?Growth of the ?-NaYF4 nanoparticles,?3?Phase transition?Ostwald ripening?,?4?Size shrinkage of the ?-NaYF4,?5?Growth of the ?-NaYF4 nanoparticles?3?Controlled synthesis of from YF3:20%Yb3+/2%Er3+ to LiYF4:20%Yb3+/2%Er3+ in mixture solutions of oleic acid and n-hexanol through solvothermal method was realized,and the effect of ratio of LiF/RE and reaction temperature on the mechanism as mentioned above has been discussed systematically.Subsequently,the optical properties of YF3:20%Yb3+/2%Er3+ and LiYF4:20%Yb3+/2%Er3+ were characterized by upconversion emission spectra and fluorescence lifetime spectra.?4?Controlled synthesis of the crystal form??,??and morphology?nanorods,nanospheres,nanoprismks?of NaYF4:20%Yb3+/2%Er3+ nanomaterial are realized using solvothermal synthesis in a mixture of oleic acid and n-hexanol by precisely adjusting the ratio of Na F/RE.In addition,the growth mechanism of ?-NaYF4 nanorods was studied.It was concluded that growth process of the nanorods mainly included the following processes: nucleation,growth??-NaYF4?,the process of Ostwald Ripening?orientation growth?,and regrowth.The luminescent color of the sample can be adjusted by the tuning of ionic species of the activator,,and the lifetime of the 4S3/2 level of Er3+,the 1G4 level of Tm3+,and the 5S2 level of Ho3+ were observed by using the fluorescence lifetime spectrum.?5?Controlled synthesis of from KY3F10:20%Yb3+/2%Er3+ to K2YF5:20%Yb3+/2%Er3+,YF3:20%Yb3+/2%Er3+ to KY3F10:20%Yb3+/2%Er3+ was achieved in the mixed solvents of oleic acid and n-hexanol by adjusting the ratio of KF/RE and temperature,respectively.The effect of reaction temperature and reactant monomer concentration on the mechanism of phase transition of the material was researched. |