The Synthesis And Luminescent Properties Investigation Of Rare-earth Lons Doped Orthovanadate And Aluminate Phosphors

With the technical development of FED and PDP, the requirement which includes the crystal size distribution, stability, luminescence efficiency, brightness and conductivity of the powder also has been improved. Since the luminescent nanomaterials have many unique functions, thus it is highly hoped that they will be a new type of luminescent material of next generation. Among the large number of luminescent nanomaterials, rare-earth vanadate host luminescent nanomaterials have a good chemical and thermal stability, but there are few investigations focused on the luminescent properties of rare-earth vanadate luminescent nanomaterials. In this thesis, we synthesized rare-earth vanadate luminescent nanomaterials through many different ways, and systematically investigated the luminescent properties to find new types of high-performance luminescent materials.(1) In the first chapter, we briefly describe the state of art of the research on luminescent nanomaterials; systematically introduce the spectrum theory of lanthanide ions and the research background of lanthanide-ions-doped luminescent nanomaterials; besides that, we generalize and review the improvement in the synthesis and surface modification of rare-earth-ions-doped luminescent nanomaterials in recent years, as well as the problems which confronts; moreover, the possible research directions in future are also summarized and predicted.(2) The synthesis method and condition of rare-earth-based luminescent nanomaterials powder have been studied in this paper. Eventually, under a determined optimum research condition, we synthesized a series of nano-scale YVO4:RE3+ (RE = Eu, Dy, Sm), Y1-xRExVO4:Eu3+ (RE = La, Gd), using citric acid as complexing agent, through the improved complexing-sol-gel method. The nanoparticles we synthesized have a uniform size, the scale of which is below 100 nm, and the smallest one can be as large as 20 nm. Under the UV irradiation, we studied the luminescent properties of the powder by the numbers. The result of the research indicates that the luminous intensity of nanoparticles increases with increasing the annealing temperature. Furthermore, as an appropriate amount of La³⁺ and Gd³⁺ doped into YVO4 host, the luminous intensity is also improved as a result of the distortions of crystal structure. (3) 4F9/2 - 6H13/2 transition of Dy3+ in YVO4:Dy3+ belongs to electric dipole transitions (?J = 2), which can be easily influenced by the surroundings. Besides that, YVO4 has the same crystal structure as YPO4, thus YVO4 and YPO4 can easily form solid solutions. Based on the reasons discussed above, we successfully synthesized YPxV1-xO4:Dy3+ luminescent nanoparticles by citric acid sol-gel method. The luminescent nanoparticles we got are close to sphere and have a sharp size distribution. After the relationship between the molar ratio of V/P in YPxV1-xO4:Dy3+ and the color of nanoparticles under the irradiation of UV was studied by the numbers, we found that with the decline of V/P molar ratio, the color gradually changes from yellow to blue. And in the range that X=0.775-0.85, the emission color is white. YPxV1-xO4:Dy3+, therefore, can be a new type of white-emission material. However, as a material to put into practical applications, some of its performances such as brightness still need to be improved.(4) Luminescent powder of SiO2@YVO4:Eu3+ core-shell structure was successfully synthesized by simple citric acid sol-gel method. Through controlling the condition of solution concentration, the mass ratio of core/shell, the annealing temperature, and the thickness of shell, we found out the most suitable coating condition. The samples we obtained not only keep the sphericity of SiO2 core but also have the radiation characteristic of pure YVO4:Eu3+. The shell we prepared is tight, uniform, smooth texture, and has no crack, the thickness of which can be controlled within 50-100 nm. Moreover, under 800 oC, YVO4:Eu3+ can crystallize well on the surface of SiO2, which greatly reduce the reaction temperature. The characterization results which are used to explain the formation mechanism of core-shell structure indicate that the hydroxyl on the surface of SiO2 and the viscosity of precursor solution play a crucial role. The emission lifetime of Eu3+ ions and PL emission intensity were both increased with increasing annealing temperature and the thickness of the shell. As the mass ratio of core/shell increases to 60%, the emission intensity of SiO2@YVO4:Eu3+ core-shell structure reaches to 91% of that of pure YVO4:Eu3+.(5) We respectively synthesized high-quality YVO4:Eu3+ micro-rod crystal array and flower structure crystal on the underlay of amorphous glass, using Na2H2L·2H2O to complex metal ions, through hydrothermal method, and we did not use any surfactant and template. Micro-rod crystal array epitaxially grew on the glass substrate which was covered with YVO4:Eu3+ crystal-seed layer under low temperature and using sol-gel method. Meanwhile, flower structure grew on glass substrate which did not have crystal seed. Through SEM, we observed that high-quality and large area of YVO4:Eu3+ micro-rods were perpendicularly grown on the substrate. The lengths of the micro-rods are roughly the same, and they have a tight and uniform distribution and the length of every micro-rod was approximately 4μm. The cross section of micro-rod was an obvious rectangle and the size of it was in the range from 300×300 nm2 500×800 nm2. The flower structure was composed of many rectangle micro-rods which radiate to all direction. Every single rod had rectangle cross-section and definitive crystal facet. Moreover, we discussed the growth mechanism of micro-rods in the solution of this system and also pointed out its impact on the morphology. Based on the growth mechanism we studied the cause of formation, which provides a possible technical approach to form YVO4:Eu3+ micro-rods of different morphology and optimize them. The result indicates that YVO4:Eu3+ micro-rods with different morphology all belong to zircon structure, whose a-axis is the optimum orientation of these deposited YVO4:Eu crystals.(6) We synthesized REMAl3O7(RE = Gd, La; M = Ca, Sr) luminescent nanomaterials through citric acid sol-gel method, and used XRD, AFM, SEM, TEM and PL to characterize the nanoparticles. The characterization result indicates that single-crystal luminescent nanoparticles are engendered under 800 oC annealing. The nanoparticles have sphericity morphology, the mean size is less than 100 nm, and with the rise of annealing temperature the crystal becomes more perfect and the size of nanoparticles also increases. Compared with solid-state reaction at high temperature, the annealing temperature declines by 600 oC . Under the irradiation of UV, the example radiates intensive red and green light, which respectively accord to the 5D0– 7F2 transition of Eu3+ and the 5D4–7F5 transition of Tb3+. Besides that, the emission intensity also increases with the increasing annealing temperature and the amount of Eu3+ ions (or Tb3+) doped in the host.