硒化鎘/硫化鋅膠狀量子點之時間解析光激發螢光研究

我們以up-conversion技術及時間相關單光子計數系統量測得到的時間解析光激發螢光資料探討CdSe/ZnS膠狀量子點及SiO2/CdSe/SiO2三明治結構的超快載子動態行為、光激發螢光強度隨著時間的變化，以及超快載子動態行為隨著時間的變化。我們使用的是球核-球殼量子點，ZnS球殼可以鈍化CdSe球核表面的懸空鍵，所以以up-conversion技術量到的曲線中並沒有皮秒等級的衰減分量。另外，量測到CdSe量子點的升起時間為537飛秒。 CdSe量子點在空氣中會因光照射而氧化，氧化生成物直接捕獲激發的載子，加上非輻射性復合的效應增加，使得強度大幅變弱。而製作SiO2/CdSe/SiO2三明治結構可以隔開CdSe與氧氣，避免CdSe因光照射而氧化。製作成三明治結構後，強度有比較弱是因為在製作三明治結構的製程有升溫，使得CdSe的表面結構改變，更多缺陷形成，非輻射性復合變多。而以光照射三明治結構可以重組表面結構減少缺陷，使PL變強。另外，也以μ-PL系統進行量測，也就是以高功率密度照射CdSe量子點。CdSe量子點在高功率密度照射下，激發的載子直接進入trap，非輻射性復合增加，強度變弱。而接著換成小功率密度照射，因為重組因光照射而改變的表面結構，強度變強。

關鍵字

硒化鎘；量子點；膠狀量子點；時間解析光激發螢光

並列摘要

In this thesis, we use time-resolved photoluminescence data measured with up-conversion technique and time-correlated single photon counting system to study the changes of photoluminescence intensity and ultrafast carrier dynamics over time in CdSe/ZnS colloidal quantum dots and SiO2/CdSe/SiO2 sandwich structure. Because the dangling bonds on the CdSe surface can be passivated by ZnS shell, there is no picosecond decay in the curve measured with up-conversion technique. Besides, the photoluminescence rise time in CdSe quantum dots is 537 fs. CdSe quantum dots can be photooxidized in air. Oxidation-generated species can capture excited carriers. This effect and nonradiative recombination result in photoluminescence decay. In the SiO2/CdSe/SiO2 sandwich structure, oxygen is blocked by the outer SiO2 layer, thus photooxidation does not occur. The photoluminescence of the SiO2/CdSe/SiO2 sandwich structure is weaker. The CdSe surface was transformed and defects were generated during high temperature SiO2 growth process. This effect causes nonradiative recombination and weaker intensity. But we observed photo-induced photoluminescence enhancement in SiO2/CdSe/SiO2 sandwich structure. This photoluminescence enhancement is attributed to restructured surface and reduced defects. Furthermore, we use μ-PL measurement system. In other words, CdSe quantum dots are irradiated with high power density. During high power density irradiation, carrier trapping causes nonradiative recombination and photodarkening. After darkening, photoluminescence enhancement is observed with low power density irradiation. This enhancement is also attributed to restructured surface.

並列關鍵字

CdSe ； quantum dot ； colloidal quantum dot ； time-resolved photoluminescence

參考文獻

[10]Jia-Min Shieh, Yi-Fan Lai, Yong-Chang Lin, and Jr-Yau Fang, “Photoluminescence: Principles, Structure, and Applications”, 奈米通訊第十二卷，第二期，28-39 (2005)

[5]Kyung-Sang Cho, Eun Kyung Lee, Won-Jae Joo, Eunjoo Jang, Tae-Ho Kim, Sang Jin Lee, Soon-Jae Kwon, Jai Yong Han, Byung-Ki Kim, Byoung Lyong Choi, and Jong Min Kim, “High-performance crosslinked colloidal quantum-dot light-emitting diodes”, Nature Photonics 3, 341-345 (2009)

[1]Sjoerd Hoogland, “The Fuss About Quantum Dots”, Photonics Spectra 42, 80-81 (2008)

[3]Seth Coe-Sullivan, “Optoelectronics: Quantum dot developments”, Nature Photonics 3, 315-316 (2009)

[4]Wendy U. Huynh, Janke J. Dittmer, William C. Libby, Gregory L. Whiting, A. Paul Alivisatos, “Controlling the Morphology of Nanocrystal-Polymer Composites for Solar Cells”, Adv. Funct. Mater. 13, 73-79 (2003)

國際替代計量

硒化鎘/硫化鋅膠狀量子點之時間解析光激發螢光研究

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