Spherical CdSe quantum dots (QDs) with a narrow size distribution were synthesized using a refined phosphonic-acid-assisted organometallic route. Visible absorption spectra show that as reaction time increases the absorption peak will shift to longer wavelength. HRTEM image confirmed the high-crystallinity of the as-prepared QDs. Raman spectroscopy was used to investigate the size and temperature dependence of the phonon spectra. As temperature increases, the LO-phonon frequency will decrease and the bandwidth will increase. As size increases, the LO-phonon frequency will increase and the bandwidth will decrease. However, when the temperature is above 400 K, the LO-phonon frequency in the smaller dots is higher than that in the larger dots due to the weaker negative temperature dependence of the LO-phonon frequency in the smaller dots.
Effect of ZnS shell thickness on the phonon spectra in CdSe quantum dots