Combinatorial Materials Libraries Liquid Phase Parallel Synthesis And Combinatorial Screening Of The Red Vacuum Ultraviolet Fluorescent Material Sensitizer

The demand for high performance phosphors under vacuum ultraviolet (VUV) excitation increased greatly because of the development of plasma display panels (PDP) and Hg-free lamps. Combinatorial approach is a high efficient method for novel materials screening. The development on VUV phosphors research will be improved greatly with combinatorial approach adopted. Among various parallel synthesis strategies, thin film deposition combined with a physical mask (or photolithography) and solution based synthetic methods are the most commonly used techniques. As for luminescent library, it is better to be synthesized with solution based method, because the photoluminescence spectra of the large number of discrete samples that prepared with thin film deposition are difficult to test. Inkjet delivery shows many advantages over other micro-dispense apparatus adopted in solution based combinatorial synthesis, such as nano-liter dispensing capability with high accuracy and non-contact etc. A drop-on-demand micro piezoelectric inkjet delivery system was developed in our group, which can be used in combinatorial synthesis. However, a significant limitation to inkjet is that only soluble compounds can be used as precursors in combinatorial synthesis. In addition to that, many materials are insoluble. To meet for the requirement of inkjet technique in combinatorial synthesis, a universal method to prepare suspension is developed, and the applicability of the combinatorial library synthesis from suspension using inkjet technique is verified. Parallel synthesis and high through-put screening are the two critical factors that restrict the efficiency of combinatorial approach. To meet the demand of high through-put screening for VUV phosphor library, a combinatorial VUV excited luminescence characterization instrument is developed. For VUV luminescent materials research, different hosts are searched with combinatorial approach at first, then the sensitizers of the activator of Eu³⁺ are optimized. Finally, the energy transfer mechanism of the optimized new materials is studied. This thesis is organized according to the above logic.Chapter one is the background of solution-based combinatorial parallel synthesis using inkjet technique and the advance in VUV excited red phosphors research. First, the basic concept, principle and history for combinatory materials science are introduced, and the development for combinatorial library design, synthesis, characterization, and data mining are summarized, especially combinatorial synthesis technique and high through-put characterization. Second, the principle of inkjet technique and its application in free-forming, micro fabrication, and materials science are summarized. The home-made drop-on-demand piezoelectric inkjet delivery system is also introduced in this section, including the structure, principle of droplets inkjetting, and system stability. Third, the technical principle of PDP and problems existed in current used three-primary color phosphors for PDP are discussed, and the latest progress in red VUV phosphor research and combinatorial approach screening for VUV phosphor are summarized, especially the properties of borates and phosphates phosphor under VUV excitation. Finally, the borate structure and mechanism of energy transfer under VUV excitation is summarized.Chapter two is our research on solution-based combinatorial parallel synthesis using inkjet technique by inkjetting ultrafine/nano suspension. First, a universal method to prepare ultrafine/nano particles suspensions of insoluble oxides in pure water is explored, which makes full use of mechanical-chemistry effect on particle's surface modification during ball milling in pure water. At the same time, the effects of ball milling time and rate on the stability of suspensions and particles' size, profile, and structure are investigated. The applicability of combinatorial synthesis from the ultrafine/nano particles suspension using a drop-on-demand inkjet delivery system is verified by synthesizing a photoluminescent library. The structure and photoluminescence properties of the micro samples in library are consistent with that of bulk samples.Chapter three is the designing and manufacturing of the combinatorial VUV excited luminescence characterization system. The selection of VUV light source, the design of vacuum chamber, and the evaluation and demonstration of system properties are described in details. The theoretical calculation guarantees that this system can meet our requirements, and in fact such an instrument is manufactured with photography. The luminescence of combinatorial library under 147nm excitation can be characterized at one time using this system, but one of shortcoming of this system is its systematic error. To overcome systematic error, a software is developed to process the library luminescence images helpfully.Chapter four is our research on combinatorial screening sensitizers for red phosphors under VUV excitation. The combinatorial libraries are all synthesized with inkjet technique, and the VUV excited luminescence is characterized with the home-made combinatorial VUV excited luminescence characterization system. First, the Eu³⁺ co-doped Y₂O₃-B₂O₃-P₂O₅-SiO₂ system is screened with combinatorial approach. The Eu³⁺ co-doped Y₂O₃-B₂O₃-P₂O₅-SiO₂ tetrahedron system libraries are synthesized at 1150°C, 1250°C, 1350°C, and 1450°C respectively. The result demonstrates that among Y₂O₃-B₂O₃-P₂O₅-SiO₂ tetrahedron system YBO₃ synthesized at 1150°C is the best host that can sensitize Eu³⁺ luminescence under 147nm excitation. Secondly, Pr³⁺/Tb³⁺/Sm³⁺/Bi³⁺ co-doped (Y,Gd)BO₃:Eu³⁺ system is screened with combinatorial approach. The experiment results demonstrates that Bi³⁺ can sensitized Eu³⁺ luminescence under VUV excitation, and trace of Pr³⁺/Tb³⁺ is helpful to improve Eu³⁺ luminescence intensity, while Sm³⁺ is unhelpful. However, with the content of Pr³⁺/Tb³⁺ co-doped increases, the quench effect of Pr³⁺/Tb³⁺ on Eu³⁺ is more serious than Bi³⁺ and Sm³⁺. Finally, the (Y_1-zGd_z)_1-x-yBi_yEu_xBO₃ system is optimized with combinatorial approach, and a new high efficiency red VUV phosphor is obtained. That is (Y_1-zGd_z)_1-x-yBi_yEu_xBO₃ (0.02≤x≤0.05 , y≤1×10^-3 , 0.1≤z≤0.2).Chapter five discusses the energy transfer in (Y,Gd)BO₃:Bi³⁺,Eu³⁺ system under VUV excitation. It is observed that the Bi³⁺→Eu³⁺ direct energy transfer does exist in YBO₃:Bi³⁺,Eu³⁺, while in (Y,Gd)BO₃:Bi³⁺,Eu³⁺, the energy transfer from Bi³⁺ to Eu³⁺ is mainly through Bi³⁺→Gd³⁺…Gd³⁺→Eu³⁺ path, that is the absorption energy of Bi³⁺ ions first transfers to Gd³⁺ ions, then transfers among Gd³⁺ lattice until trapped by Eu³⁺ ions.Several brief conclusions all through this thesis can be summarized as below:(1) A universal method for preparation ultra/nano particles suspension in pure water is explored.(2) The solution based combinatorial synthesis is extended.(3) A combinatorial VUV excited luminescence characterization instrument is developed.(4) A new high efficiency VUV phosphor is optimized. That is (Y_1-zGd_z)_1-x-yBi_yEu_xBO₃ (0.02≤x≤0.05 , y≤1×10^-3, 0.1≤z≤0.2 ).(5) The energy transfer path in (Y,Gd)BO₃:Bi³⁺,Eu³⁺ under VUV excitation is interpreted, which is mainly through Bi³⁺→Gd³⁺…Gd³⁺→Eu³⁺.