Morphology Regulation And Application Of Rare Earth Fluoride Nanocrystals

Due to distinct optical properties,lanthanide-doped upconversion nanocrystals(UCNPs)were suited to a range of applications including solid state lasers,three-dimensional displays,photocatalysis,biomedical applications.Especially in biomedical applications,UCNPs were regarded as a new generation of promising luminescent labels materials owing to their prominent merits,such as low toxicity,high signal-to-noise ratio,deep tissue penetration and lowered auto-fluorescence.Although there are a number of potential applications for UCNPs,the controlled morphology and growth mechanism of materials need to be investigated in detail to meet the demands of the applications.We selected NaYF4 and new matrix KLu2F7 as upconversion host materials,the formation mechanisms of materials and the relationship between crystal morphology and UC properties were systematically investigated.What’s more,the compound of NaYF4:Yb,Tm NPs and semiconductor ZnO were prepared and studied the photocatalysis performance under near-infrared excitation.The details were summarized as following:(1)We developed the use of oleic acid(OA)and 1-octadecene(ODE)as surfactant for the synthesis of various morphology and monodisperse NaYF4:Yb,Tm nanocrystals with changing the molar ratio of fluorine source to lanthanide compounds(F’/Ln3+)by a solvothermal strategy.The monomer concentration-based principle was proposed to interpret the morphology evolution of the nanocrystals that the morphology changing from sphere to hexagon to rod.The effect of UC properities on various morphology of NaYF4:Yb,Tm were investigated,the result indicated that the UC properities strongly depend on morphology,the effect mechanism of surface defact on UC properities was revealed by calculating and analysing the ratio of surface to volume of NaYF4:Yb,Tm nanocrystals.(2)Uniform,monodisperse,orthorhombic KLu2F7:Yb,Tm nanocrystals were successfully prepared via a solvothermal strategy.The effect of the ratio of F-to Ln3+,oleic acid and reaction time on crystal structure and morphology were carefully investigated,the result indicated that the products were nanorods with 32.1 nm×10.1 nm(lengthx diameter)when the ratio of F-to Ln3+ was equal to 5.The morphology of KLu2F7:Yb,Tm nanocrystals changed from rod to hexagon with increasing of OA,the size of KLu2F7:Yb,Tm nanocrystals became larger with prolonging the reaction time.The UC emission spectra indicated that KLu2F7:Yb,Tm nanocrystals had shown intense ultraviolet and blue emissions.Moreover,the emission intensity and fluorescence lifetime of KLu2F7:Yb,Tm nanocrystals were depended on their morphology and size.(3)We reported a facile approach for the synthesis of NaYF4:Yb,Tm@ZnO core-shell composites with the assist of ascorbic acid(AA).The influence factor of the growth of ZnO and formation mechanism of NaYF4:Yb,Tm@ZnO,including Zinc amount,pH,reaction time and ascorbic acid amount,were systematically investigated.The result indicated that Zn complex,AA and cetyltrimethylammonium bromide(CTAB)played a key role in the growth of ZnO.The UC emission and fluorescence lifetime indicated that there were energy migration between NaYF4:Yb,Tm and ZnO via fluorescence resonance energy transfer(FRET)in NaYF4:Yb,Tm@ZnO composites.After 12 h irradiation by 980 nm NIR,82%of Rhodamine B had been degraded by NaYF4:Yb,Tm@ZnO composites,which indicated that NaYF4:Yb,Tm@ZnO composites had excellent photocatalytic activity under 980 nm NIR irradiation.