利用奈米金粒子增強螢光元件之研究

Abstract

藉由入射光與金屬奈米粒子的耦合,使得金屬表面周遭產生的強大的侷域性電場，此光學特性即稱為侷域性的表面電漿共振(LSPR)，目前已經廣泛被運用在生醫檢測、光電元件等多方面上。根據準靜粒子下的米氏理論(Mie Theory)，單一金屬粒子的光場表現如同一個奈米天線發出的場型，而我們研究在於一個層狀的高分子結構中，參雜在高分子聚合物(PEDOT:PSS)中的金奈米粒子(天線)與發光高分子聚合材料中(MEH:PPV)的激子之間耦合的關係。實驗中相對於未參雜的金奈米粒子的樣本中，我們得到了2.3倍的螢光量子增益。 有研究顯示：當發光體靠近金屬表面時會增強其激發效益，然而，過於接近會導致非輻射性的能量轉換到金屬粒子上，導致發光體的量子增益下降；在實驗中，藉由調整間隙層的厚度進而改變金屬奈米天線和發光層之間的距離，可得到一理想化的相對量子螢光增益。最後將此樣品的結構運用在電制發光的高分子聚合物系統上，在同樣的電性條件下，發光的量子增益能有效提升。

Surface plasmon resonances in metallic nanoparticles are of interest for a variety of applications due to large local field enhancement that occurs in the vicinity of metal surface. Based on the quasi-static dipole approximation limit of Mie theory, a metallic nanoparticle sphere acts as a nanoantenna. In this paper, we studied the coupling between the excitons in the emission layer (MEH:PPV) and gold nanoantenna which is blended into the polymeric matrix (PEDOT:PSS) in a layer structure. Compared to the sample without Au particles mixing, surface plasmon resonance coupling to molecular excited state resulted in fluorescence enhancement of up to 2.3x in overall relative quantum efficiency. As the fluorescent emitters was in the vicinity of metal surface, the local field enhancement lead to a increased excitation probability whereas nonradiative energy transfer to particle result in a decrease of quantum yield. The phenomenon was discussed by changing the separation between gold nanoantenna and singlet polaron excitons to obtain the optimized quantum yield. In this study, the optimal thickness (thickness of spacer layer) was determined to be 30 nm. The structure can be utilized in most electroluminescent polymeric system. The results revel that the optical efficiency can be effectively enhanced without sacrificing the electric properties.