- 學位論文
有機材料結合氧化鋅之薄膜光特性應用
The Application and Optical Properties of Organic Material Combined with ZnO Thin Film
摘要
本論文的主要研究在探討如何利用全溶液製程結合有機材料和氧化鋅奈米結構製作以紫外光 LED所激發的螢光薄膜。在論文之中，我們首先介紹如何以溶膠-凝膠法製作氧化鋅薄膜以及水熱法至被氧化鋅微奈米柱以及一些本論文所會使用到的實驗儀器；利用有機材料以及氧化鋅的結合，第三章的部分我們則展示了一個全程低溫的方法制備高缺陷放光的氧化鋅奈米柱/PMMA異質結構，藉由控制適當的紫外光臭氧處理時間，PMMA上以適當的表面修飾以入親水性的鍵結，由SEM圖可以觀察到氧化鋅奈米柱成功的長於PMMA上，傅立葉紅外光穿透頻譜測量以及水滴接觸角量測皆證實了紫外光臭氧處理大大的提升PMMA表面的親水性，而適當的處理時間對於在PMMA上生長出氧化鋅奈米柱扮演著一個重要的角色，室溫光激發光頻譜顯示了氧化鋅奈米柱/PMMA異質結構在500-700nm波段有一很強的波峰，其擁有很高的IDpeak/IBpeak (其中最好的IDpeak/IBpeak是400，ID/IB為1600)； 低溫變溫光激發光頻譜實驗結果可以與阿瑞尼亞士方程式有很好的fitting，經由阿瑞尼亞士方程式所得到的活化能為77.6 meV，低的活化能也證明了我們的樣品可以很容易的引發載子復合反應，高的IDpeak/IBpeak更是可以互以低活化能的結果驗證，實驗結果顯示氧化鋅奈米柱與PMMA的介面缺陷狀態是主要有如此高IDpeak/IBpeak的原因。 接著為了補強上述只有500-700nm的放光波段，我們將藍光有機Polyfluorene結合氧化鋅奈米複合材料薄膜製作出了白光螢光薄膜；我們利用有機藍光材料PF (9,9-DI-N-hexylfluorenyl-2,7-diyl)、油性分散劑以及混參氧化鋅奈米粒子合成出螢光溶液，由FTIR頻譜得知，油性分散劑只有增加OH基的量並不會對PF產生化學反應，影響光特性；接著由PL 頻譜分析，我們發現組成PF:ZnO nanoparticles的白光主要是以兩個明顯的波長所組成：1.藍光(波峰在428nm，為PF所貢獻)，2.黃綠光(波峰在532 nm)為PF與氧化鋅奈米粒子的介面狀態所貢獻；接著為了找出最適的參雜量以得到最高的效率，我們參雜了一系列不同重量的氧化鋅奈米粒子PF:ZnO nanoparticles，計算PL EQE，其最高PL EQE效率可以達到79%，與一般市售的YAG:Ce螢光粉效率相差不遠(75%)；其中色溫的範圍是在(3862K~7674K)左右，主要以冷白光為主，最後我們將擁有最高的光激發光效率PF:ZnO nanoparticles 0.05g的螢光薄膜做簡單的Lifetime測試，經過UV光370 nm的連續照射11個禮拜之下，其放光光譜分布並沒有明顯的改變，整體白光出光量大約下降了10%左右。本章所利用的生長方法擁有低成本，大面積製程的優勢，製程簡單，又不須用到稀土元素，與一般LED所使用的陶瓷螢光粉更是大大的不同，對於未來替代紫外光激發的白光LED有非常巨大的潛力。
並列摘要
In our study, we report the application and optical properties of organic material combined with ZnO nanostructure thin film. First of all, we introduce how to obtain the ZnO thin films prepared by sol-gel method and hydrothermally prepared ZnO micro/nanorods. Then we demonstrate a low-temperature process to synthesize ZnO nanorods/polymethylmethacrylate (PMMA) heterostructures with remarkable high defect emission via an all-solution process. Through controlling the appropriate UV/ozone exposure time to induce surface modification on the PMMA, a scanning electron microscope (SEM) shows that high defect emission ZnO nanorods were successfully grown on the surface of the PMMA. A Fourier transform infrared spectra (FTIR) and water contact angle measurement verify that the UV/ozone treatment greatly enhanced the hydrophilicity of the PMMA surface. Room temperature photoluminescence spectra (PL) reveals a very weak band gap emission and extremely intense defect emission. The evaluation based on the peak ratio of defect emission to band edge emission (IDpeak/IBpeak) reveals that the peak of defect emission intensity was 400 times stronger than band edge ultraviolet emission (IDpeak/IBpeak = 400). The temperature-dependent photoluminescence spectra data was well-fit to Arrhenius law and obtained activation energy 77.6 meV. Relatively low activation energy verify that an abundant recombination center existed in our sample. Experimental data show that the interface defect states between PMMA and ZnO are mainly responsible for such a high IDpeak/IBpeak ratio. Subsequently, in order to enhance the blue emission ,we utilized blue organic material-PF(polyfluorene),surfactant and combine ZnO nanoparticles to synthesize PF:ZnO nanoparticles system. From results of FTIR, the function of surfactant is to provide OH groups to make ZnO nanoparticles dissolved in PF instead of influencing The photoluminescence spectra of PF:ZnO nanoparticles can be clearly revealed by two clear emission. One is blue emission wavelength center at 428 nm; the other is yellow-green emission with long tail wavelength center at 532 nm. The blue emission band is attributed to PF. The yellow emission is originated from the interface defect states between PF and ZnO nanoparticles. Subsequently, in order to optimize the weight of doping ZnO nanoparticles in PF:ZnO nanoparticles system, we doped a series of different ZnO nanoparticles in PF:ZnO nanoparticles system. We found that the highest PL EQE(External Quantum Efficiency) 76.06% occurs at the amount of doping ZnO nanoparticles 0.05 g in PF:ZnO nanoparticles system ,which is comparable with commercial YAG:Ce phosphor (EQE is 75%). The range of color temperature is around 3862K~7674K, the white light of PF:ZnO nanoparticles is usually cold-white. The lifetime test of PF:ZnO nanoparticles 0.05g the has exceeded 11 weeks in package with no observable degradation under continuous strong UV LED (370 nm ) exposure. The total of white light integrated PL intensity decrease about 10%. The process we use by an all-solution procedure lowers the total cost of phosphor. The material system we present has high potential to serve as a UV-excited phosphor for white-light applications.