不同結構維度的能量授者與受者之間的近場能量轉移與光色轉換

Abstract

福斯特共振能量轉移 (Förster resonance energy transfer, FRET) 是一種實現高效光色轉換的重要近場能量轉移機制，包括彩色顯示在内具有衆多應用價值。利用此機制製作元件時， 能量授者與受者之間的距離是最大化光色轉換效率的重要因素。在本研究中，我們設計實施了三個系列的實驗來探討FRET行爲， 特別是FRET效率對於授者與受者之間距離的變化關係。這三個系列實驗包括： (1) 一個藍光氮化銦鎵/氮化鎵量子井至鄰近的一個綠光量子井的FRET過程， (2) 溶液中的綠光膠體量子點至鄰近的紅光量子點的FRET過程， (3) 一個量子井至其上覆蓋量子點的FRET過程。在兩個鄰近量子井之間，不僅是它們的距離，還有量子井内的量子侷限斯達克效應 (quantum-confined Stark effect) 都會影響其FRET的行爲。在溶液中的相鄰量子點之間，FRET的行爲也由它們的相對表面電荷，相對量子點濃度以及它們的平均間距所控制。至於在一個量子井與其上鋪蓋的量子點之間，利用自組裝 (self-assembly) 技術所製作的樣品内，除了量子井覆蓋層非常薄的情況下，並未有明顯的能量轉移特徵，在這一情況下，電子直接轉移造成能量轉移可能發生。然而，當我們使用液滴塗布 (drop-cast) 的方法在樣品表面鋪蓋量子點時，就可觀察到隨距離變化的FRET行爲。從FRET效率隨距離變化的擬合結果來看，不易發現FRET效率隨距離變化與授者或受者的結構維度有什麽明顯的關係。

The Förster resonance energy transfer (FRET) is an important near-field energy transfer process for implementing effective color conversion, which can find many useful applications including color display. In fabricating such a device, the distance between the energy donor and acceptor is a crucial factor for maximizing the color conversion efficiency. In this research, three series of experiments are performed for studying the FRET behaviors, particularly the dependencies of FRET efficiency on the donor-acceptor distance. They include (1) the FRET process from a blue-emitting InGaN/GaN quantum well (QW) into a nearby green-emitting QW, (2) that from a green-emitting colloidal quantum dot (QD) into a nearby red-emitting QD in the solution, and (3) that from a QW into overlaid QDs. Between two neighboring QWs, not only their separation but also the quantum-confined Stark effect in the QWs can affect the FRET behavior. Between two neighboring QDs in a solution, the FRET behavior is also controlled by their relative surface charges and their relative QD concentrations besides their average spacing. Between a QW and overlaid QDs, the technique of self-assembly results in no clear energy transfer behavior except the condition of an extremely small QW capping layer thickness, under which a process of direct electron transfer occurs. However, based on the technique of drop-casting for overlaying QDs, a distance-dependent FRET behavior is observed. From the fitting results of FRET efficiency, it is difficult to find a close relation between the distance dependence of FRET efficiency and the structure dimension of the donor or acceptor.