奈米顆粒中位於表面之原子之比例，遠較大顆粒晶體為高，這使得奈米晶體之表現顯著的受其表面性質影響。本論文研究半導體量子點之兩種表面相關發光特性，分別為亮暗閃爍行為及低能量寬廣放光行為。觀測單一螢光分子或單一量子點，可發現其螢光會因暫時進入暗態而不發光，之後又回復發光狀態而產生亮暗交替之閃爍行為。對於量子點之亮暗閃爍行為，一般之理解為當量子點結構之光激發狀態產生電荷轉移至表面結構，導致這量子點成為帶電狀態而不發光。當量子點重新成為中性結構，便可再次被激發而產生螢光。另一方面，超小粒徑之量子點經常因表面能階復合而產生低於能隙之寬廣波長範圍之螢光。本論文探討這兩種與表面結構相關特性之間的關聯。
實驗樣品為粒徑大小2.1nm 之CdSe/ZnS 量子點，螢光中心波長在515nm 處。除了能隙對應之螢光外，放光光譜顯示另有一寬廣且無結構之發光涵蓋590 -800 nm 波長範圍，且對應不同的螢光生命期。能隙附近之放光的螢光生命期為20 ns，但在長波長範圍所得螢光生命期為200 ns ，顯示它們分屬不同放光機制，及確定寬廣放光是來自電荷轉移之低能量寬廣放光結構。進一步以CCD 連續紀錄單一量子點之對應綠光(能隙對應之放光)與紅光(低能量寬廣放光結構)之光強度變化，結果發現個別量子點僅選擇單一種放光機制進行。在超過200 個單一量子點中，大部分發出綠光，僅有少數量子點發出紅光，且沒有量子點同時產生綠光與紅光。這顯示個別量子點結構之些微不同造成極大的發光特性上的差異：少數量子點容易產生電荷轉移，因此激發狀態瞬即產生電荷轉移至表面，因此僅發出紅光；但大多數量子點並不進行類似之電荷轉移，因此持續發綠光。
進一步觀察個別量子點之螢光，發現綠光結構與紅光結構均表現亮暗閃爍行為，結果顯示低能量寬廣放光行為與亮暗閃爍是分屬不同的表面結構所造成的結果，否則便無法在紅光螢光時觀察到亮暗閃爍行為。

Nanocrystal has non-negligible ratio of the surface atoms. The photophysics of the nanocrystal is strongly influenced by the surface states.There are two surface-related phenomena: the on-off blinking and the red-emission. On-off blinking is a phenomenon commonly observed in thesingle emitters, such as dye molecules and semiconductor quantum dots (QD).In the QD, the charged state caused by the charge transferring from the core to
the surface states explains the off-state. Another surface-related phenomenon is the red-emission, which is the emission from the low-lying surface trapped states. This thesis investigates the correlation between the on-off blinking and the red-emissions of the semiconductor nanocrystals.
CdSe/ZnS core/shell colloidal nanocrystals with 2.1nm in diameter and emission peak at 515nm were examined. PL spectrum in the solution indicates that besides the band-edge emission, there is a broadband emission spanning the wavelength range of 590 – 800 nm, which is called the red-emission. The lifetime of the band-edge emission is about 20ns, and that of the red-emission is
about 200ns. Since they are with different fluorescence lifetime, the band-edge emission and the red-emission are from distinct emission species.
Emission intensity from individual QDs of the band-edge emission and the red-emission are recorded by an imaging CCD. Most QDs exhibit band-edge emission. Only few QDs show the red-emission. Both emissions exhibit clear on-off blinking, indicating the two phenomena are with different mechanism.Moreover, the band-edge emission and the red-emission are mutual exclusive.None QDs exhibit both emissions. This indicates the tiny structure difference from one QD particle to another QD particle resulting in a dramatic different of the excitation energy relaxation pathway.

摘要.................................................................................................. I
Abstract .......................................................................................... II
圖目錄............................................................................................ VI
表目錄.......................................................................................... VII
第一章 前言.....................................................................................1
第二章 量子點................................................................................6
2-1 量子點簡介..............................................................................6
2-2 量子點特性..............................................................................7
第三章 實驗理論...........................................................................11
3-1 表面性質.................................................................................11
3-2 量子點的放光閃爍行為........................................................12
3-3 寬頻譜放光............................................................................13
第四章 實驗架構及方法...............................................................16
4-1 實驗架構................................................................................16
4-2 實驗樣品.................................................................................18
4-3 實驗步驟.................................................................................19
4-4 螢光生命期.............................................................................20
第五章 實驗結果與討論...............................................................22
5-1 CdSe 量子點溶液的螢光訊號.............................................22
5-2 單一區域量子點同時量測兩種放光頻譜行為.....................24
5-3 單一區域量子點兩種放光頻譜放光動態行為量測.............27
第六章 結論...................................................................................34
參考文獻.......................................................................................35

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