Synthesis Of Rare-earth Doped Fluoride/Gold Nanostructures And Enhanced Up-conversion Fluorescence

Up-conversion luminescence?UCL?refers to the luminescence phenomenon of rare earth ions absorbing two or more low-energy photons and emitting one high-energy photon,usually referring to the conversion of near infrared?NIR?light into visible light.Up-conversion materials refer to the solid compounds doped with rare earth elements.By taking advantage of the unique metastable energy level characteristics of rare earth elements,the up-conversion materials absorb many low-energy long-wave radiation,so that the invisible infrared light can be converted into visible light.In recent years,the surface of the use of precious metals such as gold and silver nanostructures such as LAN from excimer to enhance conversion fluorescence emission reports on more and more,but for ultra-thin full gold shell coating conversion fluorescent nano material reports rarely,but also there is a larger nanoparticles and fluorescence intensity is generally weak,surface quenching/excited state molecules enhancement mechanism is unclear.Therefore,it is urgent to further explore the preparation of rare earth doped fluoride core-shell structure and how to improve the up-conversion fluorescence intensity.In the first part of this paper,two kinds of nano-gold/upconversion nanocrystalline composite structures were prepared by Wet chemistry and vacuum evaporation.The enhancement and quenching effects of local equiexcimer on up-conversion fluorescence were systematically studied.Based on the characterization of microstructure and analysis of steady state cis-fluorescence spectra,the mechanism of wavelength dependent up-conversion fluorescence enhancement and quenching was described.The results showed that the ultra-thin gold shell structure selectively enhanced the green light emission of Ho³⁺and Fe³⁺co-doped nanocrystles by 25 times,which resulted from the excitation enhancement mechanism that the excitation light energy was matched with the LSPR energy.In covered with thin nanostructured gold film on the conversion of nanocrystalline composite structure caused by the gold film is observed in the Er on conversion fluorescence quenching,to stimulate the light scattering,the gold film LSPR?local?surface plasmon resonance absorption band and green luminous energy coupling caused radiationless transition probability increases,the green light on conversion fluorescence intensity drops,UCL shorter life phenomenon.In the second part,the synthesis of NaGdF₄:Yb/Er nanometer nucleocapsid material was prepared by oil phase method.Examples of surface modification using polymers,biomolecules or proteins have been reported,but most of these methods are experimentally complex and greatly reduce the luminescence performance of up-conversion materials.Therefore,this part modifies the material by coating SiO₂.And the differences of NaGdF₄:Yb/Er,NaGdF₄:Yb/Er@NaGdF_4,NaGdF₄:Yb/Er@NaGdF₄@SiO₂,NaGdF₄:Yb/Er@NaGdF₄@SiO₂@Au were analyzed by means of transmission electron microscopy and fluorescence spectroscopy.The results show that the distribution of particles is uniform,dense and the size is controlled within 3-6 nm.Compared with the pure core,the fluorescence intensity of the NaGdF₄:Yb/Er core-shell structure is increased by about 40times,and the red light and green light are increased by 20 times and 60 times.Compared with NaGdF₄:Yb/Er@NaGdF₄ sample,NaGdF₄:Yb/Er@NaGdF₄@SiO₂ sample decreased to some extent.When the nanoparticles were successfully coated with gold shell,it was enhanced to some extent compared with@SiO₂.