Preparation Of NaYF₄@CDs Composites And Their Properties And Applications

Rare earth upconversion luminescent nanomaterials not only have strong photostability,narrow emission band,long fluorescence lifetime,high chemical stability,low potential biotoxicity,but also have a large light penetration depth by excitation with a near-infrared continuous excitation source.The remarkable advantages of no light scintillation and photobleaching,no biological tissue autofluorescence and almost no damage to biological tissues have become the application research hotspots in many fields and interdisciplinary fields.The carbon dot is a zero-dimensional semiconductor nanomaterial that is approximately spherical,which has a diameter of less than 10 nm.It is a nanocluster composed of few molecules or atoms.Compared with quantum dots with large particle diameters and molecular weights of usually several hundred thousand,the particle size of carbon dots is generally only a few nanometers.The fluorescent carbon dots with molecular weights of only several thousand to several tens of thousands are the hottest carbon nanomaterials after graphene.In this paper,properties and applications of Na YF₄@CDs composites were studied by the following research contents.(1)The blue light carbon dots with stable luminescence properties were prepared by high temperature pyrolysis method and the?-Na YF₄:Yb,Tm upconversion nanoparticles were prepared by hydrothermal method.Na YF₄:Yb,Tm@CDs were prepared by coating a surface of Na YF₄:Yb,Tm upconverting nanoparticles with a layer of 20 nm silicon dioxide and then recombining with carbon dots to stably bond the carbon dots into the silica structure.The composite material shows good dispersion and excellent dual-mode fluorescence performance.Under the action of copper ions,the luminescence of carbon dot is quenched while the up-conversion luminescence of Na YF₄:Yb,Er is not affected.So the copper ion concentration can be effectively detected.Further research found that the composite material is in the cell.Stable imaging in the medium indicates that they have great potential for application in biosensing.(2)A red light carbon dots is prepared by hydrothermal method,which has strong absorption characteristics in the wavelength range of less than 600 nm.Carbon dots act as energy acceptor materials to achieve energy transfer between CDs and upconverting particles.The easy-adjusted luminescence properties of the carbon dots and good biocompatibility give the composite more possibilities for luminescence control and biological applications.The composite material mainly utilizes the up-conversion luminescence and the carbon dot absorption light to generate energy transfer,thereby realizing the regulation of the up-conversion emission spectrum.Finally,the red light or NIR light emission ratio is much larger than the green light or blue light portions.(3)The NaYF₄:Eu,CDs solution and silica sol were mixed and mechanically stirred to form a composite solution,which was dried to form Na YF₄:Eu@CDs composite nanoparticles.When the ratio of Na YF₄:Eu to CDs is 5:1,white light emission at 395 nm excitation is obtained and a white LED is prepared.For Fe³⁺,the luminescence of carbon dots can be quenched and the luminescence of Na YF₄:Eu is not affected.A fluorescence sensor capable of detecting Fe³⁺ratio is obtained and the detection range is 0-350?M.Similarly,the CDs is much more sensitive to temperature than Na YF₄:Eu,so temperature-dependent ratiometric fluorescence sensing can be achieved with a detection range of 377-467 K.The composite material can meet the application requirements in different fields such as ion detection and white LED lamps.(4)NaYF₄:Yb,Er@CDs composite nanoparticles were successfully prepared by a simple sol-gel method.Then,bean sprouts were selected as model plants to study the germination and growth of bean sprouts after incubation with Na YF₄:Yb,Er@CDs composite nanoparticles.The bean sprout treated with Na YF₄:Yb,Er@CDs composite nanoparticles were imaged by laser confocal and it was proved that Na YF₄:Yb,Er@CDs composite nanoparticles can penetrate into various parts of bean sprouts.The wet/dry weight,root length and stem length of the bean sprouts in the treated and control groups were further tested.The data showed that the Na YF₄:Yb,Er@CDs composite nanoparticle solution can significantly promote the water absorption and growth of the bean sprouts.In addition,spraying the composite nanoparticle solution on the surface of the blade has a light-converting effect,which promotes the bean sprout photosynthesis by nearly three times.From this data,we can get a composite system that is important for the future application of nanomaterials in plants.