研究生: |
賴威穎 Wei-Ying LAI |
---|---|
論文名稱: |
溶液態MEH-PPV/ZnO中奈米粒子對光物理特性的影響 Influence of Nanoparticles in Photophysical Properties in Hybrids of MEH-PPV/ZnO in Solution State |
指導教授: |
胡孝光
Shiaw-Guang Hu |
口試委員: |
王立義
none 戴子安 none 戴龑 Yian Tai |
學位類別: |
碩士 Master |
系所名稱: |
工程學院 - 材料科學與工程系 Department of Materials Science and Engineering |
論文出版年: | 2011 |
畢業學年度: | 99 |
語文別: | 中文 |
論文頁數: | 65 |
中文關鍵詞: | 消光效應 、光激發光效率 、激子擴散係數 、激子擴散長度 |
外文關鍵詞: | quenching, photoluminescence quantum efficiency, exciton diffusion coefficient, exciton diffusion length |
相關次數: | 點閱:335 下載:0 |
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摘要
本研究藉由改變poly(2-methoxy,5-(2’-ethyl-hexoxy)-1,4-phenylene vinylene)(MEH-PPV)/ZnO nanoparticles(NPs)溶液中ZnO NPs的添加量,從UV-Vis吸收光譜和光激發光光譜分析其光學特性,探討MEH-PPV與ZnO NPs之間電荷載子的傳遞方式及其消光效應。接著再以UV-Vis吸收光譜、光激發光光譜與時間解析光激發光光譜結合Strickler-Berg equation計算MEH-PPV溶液態光激發光量子效率,並藉由文獻來輔助推論MEH-PPV/ZnO NPs溶液態光激發光量子效率之定性趨勢。由擴散控制淬熄速率數據來估算MEH-PPV/ZnO NPs溶液態激子擴散係數,之後再探討隨著ZnO NPs添加量而改變的激子擴散長度變化。此外,藉由MEH-PPV溶於不同溶劑及MEH-PPV/ZnO NPs溶液中ZnO NPs添加量的不同,從光激發光光譜中分析各電子躍遷發射帶,探討濃度、溶劑及ZnO NPs添加量對Huang-Rhys factor之影響。
由UV-Vis吸收光譜顯示隨著ZnO NPs的添加量增加,MEH-PPV的最大吸收波長會有藍位移的情形產生;而光激發光光譜的消光效應是由高分子在界面上受ZnO NPs影響所造成。由Stern-Volmer equation計算而得的消光係數(Ks),與文獻報導相比,顯示本實驗ZnO NPs(20 nm)的消光效果大於較小的ZnO NPs。
另外,隨著ZnO NPs的添加量增加,MEH-PPV/ZnO NPs溶液態光激發光量子效率之定性趨勢是下降的,且小於在純MEH-PPV溶液態的效率。MEH-PPV/ZnO NPs溶液態激子擴散係數D_E為7.1×10-4 cm2/s,與文獻報導有所差異可能是因為激子擴散係數為受發光物質的狀態及受體物種所影響。隨著ZnO NPs添加量的增加,激子擴散長度變短,即激子擴散至界面處所需的時間變短。此結果透露出ZnO NPs的含量改變,激子擴散係數不受影響,因此影響激子擴散長度的為激子生命期。
固定濃度下的MEH-PPV於不同溶劑中的Huang-Rhys factor會隨著極性增加而變大,但在極性較高的情況下,Huang-Rhys factor值的的變化不明顯。而在MEH-PPV/ZnO NPs溶液中,隨著ZnO NPs添加量的增加,使Huang-Rhys factor變小,可能是因為ZnO NPs改變了MEH-PPV周遭環境的極性,及隨後的電荷分離。
Abatract
This work is to prepare the hybrid solutions of poly(2-methoxy, 5-(2'-
ethylhexyloxy)-1,4-phenylene vinylene) (MEH-PPV)/ZnO nanoparticles
(NPs) with various amounts of ZnO NPs, and the optical properties were investigated by UV-Vis and photoluminescence spectroscopy. Furthermore, the quenching effect and the charge transfer between MEH-PPV and ZnO NPs was observed. The UV-Vis spectra, steady and time-resolved photoluminescence were combined with Strickler-Berg equation to obtain the photoluminescence quantum efficiency of MEH-PPV in solutions. With the aid of literature, the qualitative trend of photoluminescence quantum efficiency for the hybrid solutions of MEH-PPV/ZnO NPs were assessed. Data came from diffusion-controlled quenching rate was used to determine the exciton diffusion coefficient for the hybrid solutions of MEH-PPV/ZnO NPs. Further, the exciton diffusion length was studied. In addition, we analyze the vibronic bands of transitions from photoluminescence spectra for MEH-PPV dissolved in various solvents and the hybrid solutions of MEH-PPV/ZnO NPs with various amounts of ZnO NPs. Thereafter, the effect of Huang-Rhys factor influenced by concentration, solvent and ZnO NPs was discussed.
While increasing ZnO NPs, UV-Vis spectra shows the maximum absorption wavelength of MEH-PPV bands with a blue shift for these hybrids. And the quenching of PL spectra is attributed to ZnO NPs at the interface of MEH-PPV. Comparing data from the literature at ZnO NPs size =12 nm, the Stern-Volmer constant of MEH-PPV calculated from Stern-Volmer equation in this work shows better quenching effect at ZnO NPs size =20 nm.
The qualitative trend of photoluminescence quantum efficiency for the hybrid solutions of MEH-PPV/ZnO NPs are decreased with increasing ZnO NPs. Meanwhile, the photoluminescence quantum efficiency is all lower than pure MEH-PPV for the hybrid solutions of MEH-PPV/ZnO NPs. The exciton diffusion coefficient DE is 7.1×10-4 cm2/s for the hybrid solutions of MEH-PPV/ZnO NPs. With reference to literature values, it shows a effect on polymer exciton diffusion, due to the state of MEH-PPV and the species of acceptor. The exciton diffusion length is decreased with the addition of ZnO NPs, and times for the exciton diffusing to the interface between MEH-PPV and ZnO NPs are decreased. It was found that the exciton diffusion length is not influenced by exciton diffusion coefficient, but by exciton lifetime.
At same concentration, Huang-Rhys factor for MEH-PPV in various solvents increase with the polarity. However, at the condition of high polarity, the Huang-Rhys factor is not varied significantly. On the other hand, Huang-Rhys factor for the hybrid solutions of MEH-PPV/ZnO NPs was decreased with the addition of ZnO NPs. The result is due to ZnO- affected polarity of surroundings around MEH-PPV and the process of charge transfer.
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