Study On Preparation And Luminescence Properties Of Rare-earth Doped Fluorides Nanomaterials

Because the 4f electrons outside the atomic nucleus can be distributed into the 7 constituent orbitals,the rare earth elements have many electron energy levels.As a result,the rare earth ions can emit electromagnetic radiation with different wavelengths ranging from ultraviolet(UV)and visible light to the infrared zone and are ideal ion activators of lasers and luminescent materials.As luminescent materials,lanthanide-doped fluorides nanomaterials have excellent optical properties,stable physical and chemical properties,and have a good application prospect in high-resolution display,solid-state laser,infrared detection,biological analysis,medical diagnosis and other fields.However,the optical properties and liuninescence mechanism of some rare earth ions in some substrates have not been thoroughly understood because there are a variety of rare earth ions and matrix materials.The purpose of this thesis is to explore the hydrothermal synthesis,structure,morphology and luminescence mechanism of new lanthanide-doped fluorides.In this paper,we have designed and prepared a kind of BaAlF5 nanocrystalline material which can be doped with rare earth ions(Eu3+,Ce3+,Tb3+ and Eu2+).In addition,tetragonal SrAlF5 and hexagonal LaF3 nanoparticles doped and co-doped with rare earth ions(Ce3+,Tb3+)have been prepared.The luminescent properties of these lanthanide-doped nanomaterials are studied systematically.The main contents and results are as follows.BaAlF5:Eu2+nanoparticles have been prepared by hydrothermal method.XRD and SEM results show that the prepared BaAlF5:Eu2+ has an orthorhombic crystal structure,which is a rice particle with an average length of about 50 nm and a diameter of about 30 nm.By studying the fluorescence properties of BaAlF5:Eu2+ nanoparticles,it is found that the excitation center is about 260 nm and the half maximum width is about 50 nm.The emission center is 361 nm and the half maximum width is about 17 nm.The quenching behavior of Eu2+ in BaAlF5 is studied by Van Uitert and Huang models.The results show that the conclusion obtained by the two models are consistent,that is,the concentration quenching of Eu2+ is mainly caused by the electric dipole-dipole interaction.BaAlF5:Eu3+ nanoparticles have been prepared by hydrothermal method.XRD and SEM results show that the as-prepared nanoparticles belong to orthorhombic system and have a rice-shaped morphology,with an average length about 50 nm and an average diameter around 30 nm.Under the 394 nm excitation,there are six emission peaks which could be ascribed to the electronic transitions of 5D1?7F0,5D0?7FJ(J=0,1,2,3,4)of Eu3+,respectively.Because the 5D0-7F1 transition is stronger than the 5D0-7F2 transition,it is assumed that Eu3+ occupies a lattice with inversion center.Based on the Judd-Ofelt theory,the J-O intensity parameters and radiation transition rates of nanoparticles with different doping content of Eu3+ are calculated.The intensity parameters of ?2 and ?4 decreases from 1.54×10-20 cm2 to 0.845×10-20 cm2 and from 6.99×10-20 cm2 to 2.5×10-20 cm,respectively,while the radiation transition rate of 5D0 decreases from 56.6 to 31.1 s-1.Ce3+,Tb3+ mono-doped and co-doped BaAlF5 nanoparticles have been prepared by hydrothermal method.XRD and SEM results show that the BaAlF5:Eu3+ nanoparticles belong to the orthorhombic system.After co-doping with Ce3+and Tb3+,the bright green light is successfully obtained.The reason for the enhancement of green light in co-doped system is proved to be energy transfer from Ce3+ to Tb3+ by fluorescence excitation,emission spectra and Ce3+ fluorescence decay curve.The tetragonal SrAlF5 nanorods have been successfully prepared by hydrothermal method.The factors of hydrothermal reaction,such as the ratio of reactants,hydrothermal reaction time,the amount of charge compensator and the type of surfactants,has been studied.The results show that hydrothermal treatment is a necessary process for the transformation of the product from amorphous SrAlF5 structure to tetragonal SrAlF5,and the proportion of reactants is the key factor affecting the product.The fluorides,such as SrF2,SrAlF5,LiSrAlF6 or Li3AlF6,can be produced by controlling the ratio of reactants.The addition of LiCl can influence the morphology of the tetragonal SrAlF5 sample.The addition of EDTA and sodium citrate has no effect on the crystal structure of the product,and the ratio of length to diameter of the SrAlF5 sample is reduced by adding PAA.Ce3+,Tb3+ mono-doped and co-doped SrAlF5 nanorods have been prepared by hydrothermal method.XRD and SEM results show that the as-prepared nanorods belong to the tetragonal system and the average dimensions are about 1000 nm in length and 30 nm in diameter.The concentration quenching behavior of Ce3+ fluorescence is studied by Van Uitert model.It is found that the concentration quenching of SrAlF5:Ce3+ nanorods is caused by the electric dipole-electric dipole interaction.After co-doping with Ce3+ and Tb3+,the bright green light is successfully obtained.Excitation and emission spectra show that the fluorescence enhancement is due to the energy transfer from Ce3+ to Tb3+.By analyzing the spectrum,it is found that the energy transfer process of SrAIF5:Ce3+,Tb3+ nanorods from Ce3+ to Tb3+ is mainly due to the electric dipole-dipole interaction.Amino-modified hexagonal phase LaF3 have been prepared by hydrothermal method.XRD and SEM results show that the as-prepared nanoparticles belong to hexagonal system and have uniform size and good dispersity,with the average size of 30 nm.In the emission spectra of LaF3 nanoparticles with different doping contents,the emission peaks located at 488,544,584,and 621 nm are ascribed to the transitions of 5D4 to 7F6,7F5,7F4,and 7F3 of Tb3+,among which 5D4 to 7F5 is the strongest transition emission.Bovine serum protein is coupled to amino modified LaF3:Ce3+,Tb3+ nanoparticles by glutaraldehyde method.The concentration of coupling protein on the surface of Lar3:Ce3+,Tb3+ nanoparticles is measured by Coomassie brilliant blue method.The concentration of surface coupling protein is 400?g/mL(crosslinking rate is about 20%).In addition,simple cell markers were performed.