Browsing by Author "Ko, H. C."

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Antibunching Single-Photon Emission and Blinking Suppression of CdSe/ZnS Quantum Dots
(2009-10-01)
Yuan, C. T.
;
Yu, Pyng
;
Ko, H. C.
;
Huang, J.
;
Tang, Jau
We demonstrated that by property coupling to silver nanoprisms, single CdSe/ZnS semiconductor quantum dots (QDs) exhibited suppressed blinking behavior, an enhanced fluorescence intensity (similar to 2.5 fold), increased radiative decay rates (similar to 12.5,fold), and antibunching single-photon emission. All these modifications significantly promote the overall performance of the proposed single-photon sources based on colloidal semiconductor QDs.
Blinking suppression of single quantum dots in agarose gel
(2010-01-04)
Ko, H. C.
;
Yuan, C. T.
;
Lin, S. H.
;
Tang, Jau
;
應用化學系
Fluorescence blinking is commonly observed in single molecule/particle spectroscopy, but it is an undesirable feature in many applications. We demonstrated that single CdSe/ZnS quantum dots in agarose gel exhibited suppressed blinking behavior. In addition, the long-time exponential bending tail of the power-law blinking statistics was found to be influenced by agarose gel concentration. We suggest that electron transfer from the light state to the dark state might be blocked due to electrostatic surrounding of gel with inherent negatively charged fibers.
Blocked Electron Transfer and Suppressed Blinking of Single CdSe/ZnS Quantum Dots in Agarose Gel
(2010)
Ko, H. C.
;
Yuan, C. T.
;
Lin, S. H.
;
Tang, Jau
;
應用化學系
Fluorescence blinking is an interesting phenomenon commonly observed in single molecule/particle spectroscopy and has attracted wide interest recently. Such behavior in quantum dots is undesirable for applications as fluorescence markers. In this report, we observed suppressed blinking for single CdSe/ZnS quantum dots mixed in agarose gel We attributed the suppression to an increase in activation energy so that the charge transfer is blocked from the neutral light state to the charged dark state as the gel concentration increases
Environmental effects on photoinduced electron transfer and fluorescence blinking of single semiconducting nanocrystals in various matrices
(2010-01-01)
Ko, H. C.
;
Yuan, C. T.
;
Yu, Ping
;
Huang, Jane
;
Tang, Jau
In this report we explore how the surrounding environments around a single semiconducting nancrystal affect the photoinduced electron transfer, charge trapping fluorescence lifetime and fluorescence blinking. Using the time-correlated single photon counting techniques combined with confocal microscopy, we investigated photoluminescence of single CdSe/ZnS quantum dots embedded in agarose gel and on conductive substrates as examples. Understanding of the underlying mechanisms would allow us to better control of the photoluminescence properties of nanoparticles and to improve their performance in biophotonics and optoelectronics applications such as fluorescence markers, single-photon sources, photovoltaics and quantum dot lasers.
Observation of Inverted Regime Electron Transfer in CdSe/ZnS QDs from pH-Sensitive Single-Particle and Ensemble Fluorescence Measurements
(2011-07-28)
Ko, H. C.
;
Yuan, C. T.
;
Lin, S. H.
;
Tang, Jau
;
應用化學系
In this report, we investigated the pH dependence of the photoluminescence of CdSe/ZnS quantum dots (QDs). We present experimental results and theoretical analysis of both the blinking behavior of single-QDs as well as the fluorescence intensity time trace from an ensemble of QDs in agarose gel fibers at different pH environments. Such a combined approach of confined QDs by single-particle and ensemble measurements has not been used previously. This study allows us to elucidate the electron transfer processes from the light state to the dark state. The observed increase in both the activation energy for the charge transfer and the free energy gap between the light and the dark states at an increased concentration of H(+) ions supported the Marcus inverted-regime, electron transfer.