|Author's Email Address
||This thesis had been viewed 5563 times. Download 882 times.|
|| Materials and Optoelectronic Science|
|Type of Document
||Investigating the relation between non-radiative decay process and surface trap states in the CdSe quantum dots|
|Date of Defense
|| 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.
||Ming Chen - chair|
Wei-Hung Su - co-chair
Jui-Hung Hsu - advisor
Indicate in-campus at 5 year and off-campus access at 5 year.|
|Date of Submission