Investigation Of Doped Eu Luminescence And Magnetron Sputtering Target Based On BaTiO₃ Substrate

Ferroelectric materials, for example Ba Ti O3, have many special characters such as ferroelectric, piezoelectric, dielectric properties, as well as the pyroelectric, electro-optic, and acousto-optic effects. They are multi-functional materials including mechanical-thermo-photonic-electric effects. Doping rare earths and transitional metals is an important method to further improve the performances of ferroelectric materials that has being attracting attentions of researchers. The D0-7F0 transition of trivalent europium ion is a singlet that can be used as a fluorescent probe indicating the change of the crystal field. The fluorescent branching ratio of electric dipole transition 5D0-7F2 to magnetic dipole transition 5D0-7F1, can also present the microscopic local symmetry. The d-f transition of Eu2+ ion showing strong broadband emission, can be greatly modulated by the crystal field for various phosphors. The piezoelectric effect of ferroelectric materials, endows that the crystal field can be controlled by electric field for modulating luminescence in situ and reversible way. This not only enriches the means of fluorescence modulation, but also can further reveal the effect of crystal field on luminescence process. Therefore, luminescence properties of Ba Ti O3: Eu are investigated in this thesis.This work focuses upon three themes: all related to Ba Ti O3 substrate.1. Preparation and luminescent properties of Ba Ti O3: Eu3+: Ba Ti O3 nanopowder was synthesized by high temperature solid phase method, hydrothermal method, sol-gel method and coprecipitation method respectively. The effects of powder purity and the grain size on the fluorescent properties are investigated. It is observed that the maximum luminous intensity occurs at 6% of Eu3+ doping concentration. The luminescence intensity of Ba Ti O3: Eu3+ can be enhanced by attaching Ag nanoparticles and codoped with Gd3 + ions.(a) Using acetaldehyde as the reducing agent to reduce the silver ammonia solution, Ag nanoparticles are attached on Ba Ti O3 nanocrystals. With 2% Ag, the luminescent intensity of Eu3+ is two times of that without Ag, owing to the metal surface enhancement of luminescence effect.(b) The luminescence of Eu3+ in Ba Ti O3: Gd3+, Eu3+ is two time higher than that of Ba Ti O3: Eu3+. The fluorescence branch ratio of D0- 7F2 / D0-7F2 increases obviously with the change of spectral shape of D0-7F2 in comparison to that of Ba Ti O3: Eu3+. This is attributed that the codoped Gd3+ ions may cause the lattice distortion at a certain degree, and decrease the local symmetry of the lattice around Eu3+. In this condition more excitation energy is absorbed by substrate and transferred to doped ions.2. In order to prepare rare earth doped ferroelectric thin films, and control the luminescence process by electric field in situ, reversible and real-time ways, we prepared Ba Ti O3 magnetron sputtering target by isostatic pressing method, and studied the relation between target density and technological process. We observed that the sintering temperature is the biggest effect factor on the density of target. The optimum sintering temperature is 1400 ℃, where the shrinkage rate is between 17.9 % ~ 18.3%. This provides the useful reference data for the preparation of magnetron sputtering target in the lab.3. To make use of the effect of crystal field on d-f transition of Eu2+ and obtain Ba Ti O3:Eu2+ film, we study whether Eu3+ can be reduced into Eu2+ in Ba Ti O3 substrate. It is found that oxygen vacancy come from the reduction process has a great impact on Eu2+ luminescence. The emission of Eu2+ in Ba Ti O3 is around 438 nm, just overlaps oxygen vacancy absorption band(440 ~ 450 nm), thus is absorbed by the oxygen vacancy, so it is difficult to observe Eu3+ luminescence. To eliminate oxygen vacancy and ensure t ferroelectric crystalline for the piezoelectric effect, Ba Ti O3: Eu2+ must be annealed under the oxygen atmosphere. Since Ba Ti O3 don’t have tetrahedron groups, such as SO4, PO4 or BO4, which protect the doped Eu2+ ions in groups from being oxidized under oxygen atmosphere. The feasible process for preparing Ba Ti O3:Eu2+ thin film should be sputtering the target of Eu O ceramic tiles pasting on Ba Ti O3 and crystallizing on substrate in sputtering chamber.