量子侷限效應使得半導體量子點具有尺寸相關的侷限電子能階狀態，而具有優秀的光電性質。除此之外，超小(magic size)量子點另具有額外的寬廣放光光譜可涵蓋整個可見光範圍，單一尺度粒子即可成為白光光源。本論文中，利用單分子螢光測量來探討超小CdSe/ZnS量子點之寬廣放光光譜之可能機制。
溶液中的激發光譜(PL Excitation Spectrum)顯示，這些奈米粒子的寬廣放光光譜與量子點對應的能階間躍遷(band transition)之螢光來自同源。此外，我們進行單一個量子點的螢光測量。將這量子點所得螢光利用二色鏡(Dichroic Mirror)區分為兩通道，其中短波長通道主要篩選能階間躍遷之螢光，而長波長通道則篩選寬廣放光光譜之區間。這兩通道得到之螢光具有不同生命期，顯示它們之放光機制是不同的。
當進行光子相干 (photon correlation)實驗分析時，我們發現這兩通道所得螢光，在相對延遲時間約為零時，表現光子反成串(photon anti-bunching)行為。這結果與綜觀(ensemble average)實驗結果相符，顯示這些寬廣放光光譜是源自量子點光激發後形成激子(exciton)，之後再以不同機制(能階間躍遷或寬廣放光光譜)產生放光。進一步進行激發光強度控制實驗，在高激發光強度時，我們得到由多激子(multi-exciton)狀態接續產生之發光(cascade emission)。這發光程序改變反成串實驗之結果，使得延遲時間約為零之光子串發生機會不再為零，而具有時間之先後順序：能階間躍遷產生之螢光之發生會前於寬廣放光光譜之發光。這些結果顯示，兩不同發光機制間，彼此是來自同源，直到產生螢光為止，而最有可能的機制為電荷轉移狀態，亦即類似於type II量子點結構產生的螢光。

Because of quantum confinement, semiconductor quantum dots have size dependent electronic states, and the corresponding optic properties. Besides, ultrasmall quantum dots have additional red-side broadband emission, which can cover visible light. Suitable controlling the size thus can be a good candidate for the white light emitting material. In the dissertation, we study broadband emission mechanism of ultrasmall CdSe/ZnS quantum dots by single molecule detection system.
Photoluminescence excitation spectrum in the solution indicates that the broadband emission and band transition fluorescence come from the same excitation. In addition, we measure the emission spectrum of single quantum dot, which also shows the similar broadband red-emission. The emission is separated into red emission and blue emission by a dichroic mirror. Blue emission channel is for the band transition fluorescence and red emission channel is for broadband emission. Fluorescence from two channels have different decay dynamics, which indicate the different emission mechanism.
According to Hanbury Brown and Twiss experiments, we obtain the photon anti-bunching behavior at zero delay time. The result is consisted with ensemble average results that the exciton from quantum dot would choose either blue emission or red emission to release its excitation, but only single photon were emitted at each excitation. When increasing the laser power, we observe cascade emissions from multi-exciton. Antisymmetric bunching behavior at zero delay time indicates strong correlation between the two channel’s arriving photons. Summing over the results, we conclude that the red-emission is from an electron transfer state that either electron or hole trapped in the surface states, but the counter carrier delocalized in the QD, which is very similar to the emission from the type II semiconductor structure.

目綠
第一章 緒論
1-1 研究背景和動機………………………………1
1-2 研究問題………………………………………2
1-3 研究目的………………………………………3
第二章 量子點
2-1 量子點…………………………………………5
2-2 量子點特性及應用……………………………6
2-3 半導體………………………………………..11
2-4 半導体量子點………………………………..14
2-5 量子點的製作方法…………………………..16
2-6 寬頻譜放光之歷史回顧……………………..17
第三章 實驗理論分析
3-1 螢光簡介
3-1-1 螢光的機制……………………………20
3-1-2 螢光量子效率…………………………24
3-1-3 螢光非等向性…………………………24
3-1-4 螢光生命期……………………………25
3-1-5 螢光相關光譜…………………………26
3-1-6 光子反成串……………………………27
3-2 量子點能態與放光機製
3-2.1 激子…………………………………….30
3-2.2 TypeI 與Type II ……………………..33
第四章 實驗架構及方法
4-1 實驗架構………………………………………35
4-2 實驗樣品………………………………………36
4-3 實驗步驟………………………………………38
第五章 實驗結果與討論
5-1 單一CdSe量子點的放光頻譜量測結果.........40
5-2 CdSe量子點的螢光訊號量測結果…………..44
第六章
結論………………………………………………..51
第七章 參考文獻…………………………………………..54

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