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.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0802107-000711 |
| Date | 02 August 2007 |
| Creators | Chen, Yi-Cheng |
| Contributors | Chao-Kuei Lee, Yi-Jen Chiu, Jui-Hung Hsu, Ann-Kuo Chu |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0802107-000711 |
| Rights | campus_withheld, Copyright information available at source archive |
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