| Rare earth doping luminescent nanomaterials have always been a keen research hotspot,due to their narrow band spectrum,bright color,high luminous efficiency,excellent physical and chemical stability.Among the luminescent materials,nanometer luminescent materials have higher luminous efficiency because the matrix size belongs to nanometer level.Therefore,using rare earth elements to accurately regulate the spectrum and analyzing the luminescence mechanism is conducive to promoting the progress of luminescent materials and broadening the applications in the fields of display imaging,electronic communication equipment and anti-counterfeiting.Electrospinning is known to be an effective technique to fabricate polymer or inorganic fibers with diameters ranging from 10 nm to a few microns.The method possesses the advantages of low cost,easy operation,no pollution and suitable for industrial production.By adjusting the properties and processing conditions of the solution,electrostatic spinning nanofibers can be made into various shapes,such as nanowires,nanorods,nanobelts etc.In addition,cooperating rare earth nanoparticles with electrospun nanofibers can not only achieve higher luminous efficiency,but also produce various functional materials.The precondition of ideal rare earth doped luminescent material is to select suitable matrix and rare earth ions.Aluminum oxide phosphors are non-toxic and environmentally friendly,and are the most widely used materials in the luminescent material system.Especially,the alkaline earth aluminate system is one of the best luminescent materials.Consequently,in this thesis,strontium aluminate was selected as the matrix,different rare earth ions were doped,and various nano fibers were synthesized by electrospinning technology.Moreover,the phosphors were co-spun with polymer polyurethanes to prepare functional film materials.Then,XRD,SEM?TEM and spectral tests were used to study the crystal structure,microstructure,luminescence characteristics and optical applications of the samples in detail.The main results and conclusions are as follows:(1)The SrAl2O4:Ho/Yb nanowires were synthesized via electrospinning method with aluminum nitrate and strontium nitrate as the source.Employing Ho ions as activator and Yb ions as sensitizer,the upconversion luminescence properties of SrAl2O4 and its application in the field of temperature sensing were investigated.Under the excitation of 980 nm,the sample emits green light,and the spectrum shows the emission characteristic peak of Ho3+.Then the sample was heated in the temperature range of 308-508 K,the spectral changes of the sample were recorded,and the two thermo-coupled energy levels of 5F4 and 5S2 were selected for analysis.The results show that the maximum sensitivity obtained by FIR fitting to the two thermally coupled energy levels of Ho3-,5F4 and 5S2,is 2.2%K-1 at 308 K.(2)Using strontium aluminate as matrix and Eu and Yb as doped ions,pure Eu/Yb co-doped SrAl2O4 nanofibers were obtained via electrospinning technique.The spectrum of SrAl2O4:Eu/Yb nanofibers was regulated by adjusting the annealing atmosphere,changing the valence state of Eu which utilized the different luminescence characteristics of Eu3+ and Eu2+.The results display that when the samples annealed in the oxidizing environment,only the up-conversion luminescence performance is shown,which attributed to the characteristic emission peak of Eu3+.However,when the samples annealed in the reducing atmosphere,only the down-conversion luminescence occurred,which was caused by the 4f-5d transition of Eu2+.After partial oxidation treatment,there are both up-conversion luminescence and down-conversion luminescence in the same sample.(3)The SrAl2O4:Eu2+@TPU anti-counterfeiting film was successfully prepared by electrospinning.The precursor solution was composited with with high polymer polyurethane(TPU)and inorganic SrAl2O4:Eu2+phosphor.The morphology and chemical structure showed that SrAl2O4:Eu2+ phosphors were evenly distributed in TPU matrix.The obtained film not only retains the original optical properties of phosphors but also has flexibility,elasticity,transparency and water resistance.Through the tensile property test,the optical intensity of the thin film is reduced under the action of tensile force,which is due to the concentration reduction caused by the tensile area.Tailored green patterns were observed when the film was excited by ultraviolet light,but has no trace when it was exposed to sunlight.SrAl2O4:Eu2+@TPU thin film is a kind of ultraviolet fluorescent anti-counterfeiting film,which can be applied in the field of optical anti-conterfeit. |
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