Spectroscopic Properties And Luminescent Mechanisms Of Rare Earth Ions Doped Light-converting Barium-gadolinium Zincate Phosphors

Recently, luminescent materials, especially rare earth doped phosphors, have experienced an increasing research interest due to the development of lightening, display, fluorescent labeling and so on. Many efforts are devoted to improving luminescent efficiency of phosphors. Besides, reducing manufacturing costs, seeking facile preparation methods and developing environment-friendly materials are also imperative tasks for researchers. Only having a good knowledge about the instinct properties of luminescent materials in advance, we can improve their performance by deeper studies. Generally, phosphors can be divided into two types according to different luminescent mechanisms, namely up-and down-conversion phosphors. Among down-conversion phosphors, quantum cutting phosphor seems to be special for the process can be seen as the inverse of upconversion process. In this dissertation, BaGd2ZnO5and Ba5Gd8Zn4O2were chosen to be the host materials due to their excellent crystal stabilities and low-phonon-energy properties. By doping different kinds of rare earth ions in BaGd2ZnO5and Ba5Gd8Zn4O21, different types of light converting phosphors can be obtained. The luminescent properties and mechanisms are studied in detail. The main contents in this work are as follows:(1) A set of Ba5Gd8Zn44O21:Er3+, Yb3+upconversion phosphors were prepared via a solid state reaction. The doping concentrations of Er3+and Yb3+were optimized to get the intensest red upconversion emission. Compared with commercial Y2O3:Er3+, Yb3+upconversion phosphor, the Ba5Gd8ZnO21:Er3+, Yb3+phosphor shows higher upconversion efficiency.(2) A series of BaGd2ZnO5:Eu3+quantum cutting phosphors were prepared by a solid state reaction. Excitation spectra in a region upto vacuum ultraviolet (VUV) were measured by monitoring red emission of Eu3+:5D0â†'7F2, and the emission spectra were also measured under ultraviolet and VUV excitation. The quantum cutting process of Gd3+-Eu3+couple in the as-prepared phosphor was studied and the quantum efficiency was calculated.(3) A set of Ba5Gd8Zn4O21:Eu3+phosphors were synthesized by a solid state reaction. Excited by276and395nm, the samples showed different emission spectra. It was found that the samples with low Eu3+concentrations exhibited stronger upper5DJ (J≠0) emissions. Rooted in analyses on the energy level diagram of Eu3+, the luminescence mechanisms of different excitation path were discussed. The color coordinates were calculated. The samples with low Eu3+concentration emitted white light when the excitation wavelength was395nm. As the doping concentration increased to20mol%, the emission was very close to the standard red color. The dependence of emission intensities on Eu3+concentrations and the energy transfer mechanisms were studied based on Van Uitert’s model. Temperature quenching behavior was also studied and the main mechanism which quenched the fluorescent was crossover process. The activation energy for crossover was calculated by Arrhenius formula. J-O parameters for Eu3+were calculated.(4) Ba5Gd8Zn4O21:Dy3+phosphors were synthesized by a solid state reaction. The concentration and temperature quenching behaviors were studied. The temperature quenching mechanism was attributed to crossover and the activation energy was calculated.