|dc.description.abstract||Semiconductor nanocrystals (NCs) are a very active research field because of their wide emission wavelength and high quantum yields (QYs). In recent years, most studies of semiconductor NCs have focused on the preparation of different color-emitting NCs by changing particle sizes or constituent stoichiometries. However, few attentions have been paid to investigate the preparation of various color-emitting NCs through surfactant control.
In this study, high quality CdSe and ZnCdSe NCs have been successfully synthesized by the high temperature organometallic procedure (320 oC). Hexadecylamine (HDA) and trioctylphosphine oxide (TOPO) are used as surfactants, and the effect of surfactant ratios on the physical properties of NCs has been also elucidated. The elemental compositions, crystal structures, particle sizes, and optical properties of CdSe and ZnCdSe NCs are systematically investigated by inductively coupled plasma-atomic emission spectrometer (ICP-AES), X-ray diffraction (XRD), high resolution transmission electron microscope (HRTEM), UV-visible absorption spectroscopy (UV-vis), and Fluorescence spectroscopy (FL), respectively. The QYs of various CdSe and ZnCdSe NCs are also compared.
The obtained CdSe and ZnCdSe NCs synthesized with different surfactant ratios all have zinc blende cubic structures and their elemental composition is about CdSe and Zn0.20Cd0.80Se, respectively. When the amount of HDA increases from 0 to 75 wt %, the particle size of CdSe and ZnCdSe NCs decreases from 5.6 to 4.6 nm, and 6.3 to 4.9 nm, respectively. UV-vis and FL spectra display the same tendency as HRTEM results, suggesting that as the particle size decreases, the FL of NCs have a blue shift obviously. For CdSe and ZnCdSe NCs, the emission wavelength changes from 552 to 514 nm, and 620 to 525 nm, respectively. On the other hand, when CdSe and ZnCdSe NCs are synthesized with sole HDA without TOPO, the size of CdSe and ZnCdSe NCs are 5.3 and 5.1 nm, respectively, and this increase in particle size is due to the instability of metal salts in high temperature. The emission wavelength of CdSe and ZnCdSe NCs are 548 and 538 nm, respectively, implying a red –shift is noted in the FL spectra.
In terms of QY, with the amount of HDA increases from 0 to 100 wt %, the QY of CdSe and ZnCdSe NCs increases from 3 to 46 % and <1 to 43 %, respectively. In addition, the FL fwhm of CdSe and ZnCdSe NCs is noted from 36 to 24 nm and 37 to 24 nm, respectively. As a result, CdSe and ZnCdSe NCs with various emission wavelengths and QYs can be prepared by changing the surfactant ratios of HDA and TOPO. Besides, HDA is a good surfactant to prepare CdSe and ZnCdSe NCs with high QYs and narrow size distribution.