- 學位論文
膠體硒化鎘量子點之時間解析螢光研究
Studies of time-resolved fluorescence in colloidal CdSe quantum dots
摘要
本文利用溫度變化及氣體壓力變化研究Ⅱ-Ⅵ族硒化鎘/硫化鋅（CdSe/ZnS core/shell）量子點在光激螢光和時間鑑別光激螢光的光學特性。在9 K下的載子生命期利用雙指數衰減函數擬合，取得一快(τ1)一慢(τ2)的載子生命期，隨著溫度增加到200 K，τ1和τ2 有增加的趨勢。我們解釋載子生命期的增加是來自於有限的空間同調效應(finite spatial phase-coherence effect)。由載子生命期在不同能量和溫度下的現象，我們推論快和慢的載子復合分別屬於核內非侷域態和介面侷域態。 另外，我們研究膠體量子點在空氣和氧氣壓力下的光激螢光現象，隨著氣體壓力增加至一大氣壓時，光激螢光強度會有增加的現象，這是由於氧氣會鈍化量子點表面的缺陷。當隨著空氣和氧氣壓力增加時，CdSe/ZnS量子點的載子生命期隨之增加。氣體壓力增加造成的載子生命期增加，可由表面的缺陷被鈍化現象和電子侷限效應來解釋。
並列摘要
Photoluminescence (PL) and time-resolved PL (TRPL) in colloidal Ⅱ-Ⅵ CdSe/ZnS quantum dots (QDs) were studied at different temperatures and under different atmospheres. The PL intensity shows a biexponential decay at 9 K, consisting a fast component ( ) and a slow component ( ). It is found and increases at temperatures below 200 K. We suggest that the increase of the decay times at higher temperatures is due to a finite spatial phase-coherence effect. Based on the emission energy and temperature dependence of the lifetimes, we suggest that the fast and slow PL decay involves recombination of the delocalized and localized states, respectively. In addition, we study PL of colloidal CdSe/ZnS QDs in air and oxygen atmospheres. The intensity of PL has been found to enhance as the pressure of gas increases from vacuum to 1 atm. This enhancement is explained by the passivation of the surface defects by oxygen. The lifetimes ( and ) of the PL decay of CdSe/ZnS QDs increase as a function of the air and oxygen pressure. The passivation of the surface defects and the electronic confinement effect is used to account for the increase of and with increasing the gas pressure, respectively.