Research On The Effects Of NH₃·H₂O Pretreatment On The Fabrication Of Titania Nanocoating On The ZnS Phosphors Surface

Field emission displays (FEDs) is a newly developed flat panel displays. FEDs operate at low voltages and high current densities. ZnS-based phosphors which were widely used in cathode ray tube (CRTs) were easily to accumulate much electronic on the ZnS surface under this environment. It not only reduces the electron beam energy, but also has effects on the phosphors surface. ZnS surface will be oxidized into dead layers which reduce the luminous brightness and luminance intensity. One effective way is to coat phosphors with protective layers to prevent the phosphors from aging. In the former study of our team, using titanium diethanolamine complex as the precursor, titania nanocoating has been successfully obtained by sol-gel method in an aqueous solution for the first time. However, the addition of surfactant CTAB is easy to cause the formation of free TiO₂ particles. In our study, a new way to fabricate titania nanocoating was presented, that is NH₃·H₂O pretreatment with ZnS suspension. This study is focus on the enhancement of ZnS phosphors luminescent properties and stability; it has great significance for the FEDs to achieve a technical breakthrough. Main research contents:(1) Fabricating titania-coated ZnS phosphors without the addition of surfactant CTAB.(2) Under the addition of surfactant CTAB, two influence factors are discussed: the adsorption between ZnS phosphors and CTAB, concentration of titanium diethanolamine complex.(3) Using NH₃·H₂O to pretreat ZnS phosphors. The effects of pretreatment time, pH and the weight ratio of TiO₂ to ZnS were studied and the optimal coating condition was determined; the reaction process was analyzed; the mechanism of the coating was studied and based on the results, it can be inferred that the coating might be in the form of Zn-O-Ti chemical binding combination; the microstructure, chemical composition and the optical performance of the titania-coated ZnS phosphors were studied by FE-SEM, HRTEM, XPS, EDX, XRD and PL.Under the pretreatment of NH₃·H₂O, the best reaction condition is: the pretreatment time is 24h, pH is 9, the weight ratio of TiO₂ to ZnS is 5% and reaction time is 30h. The coating was uniform and continuous and there are no free TiO₂ particles.