Title page for etd-0823111-093909


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URN etd-0823111-093909
Author Chang-han Tsai
Author's Email Address m983100035@student.nsysu.edu.tw
Statistics This thesis had been viewed 5563 times. Download 882 times.
Department Materials and Optoelectronic Science
Year 2010
Semester 2
Degree Master
Type of Document
Language zh-TW.Big5 Chinese
Title Investigating the relation between non-radiative decay process and surface trap states in the CdSe quantum dots
Date of Defense 2011-07-22
Page Count 46
Keyword
  • charge transferring
  • surface state
  • quantum dot
  • broadband emission
  • on-off blinking
  • Abstract     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.
    Advisory Committee
  • Ming Chen - chair
  • Wei-Hung Su - co-chair
  • Jui-Hung Hsu - advisor
  • Files
  • etd-0823111-093909.pdf
  • Indicate in-campus at 5 year and off-campus access at 5 year.
    Date of Submission 2011-08-23

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