Size-dependent energy spacing and surface defects of CdSe quantum dots in strong confinement regime

Transmission electron microscopy and UV–Vis spectroscopy can be used to observe the individual crystallite morphology and the origin of optical activity of quantum dots (QDs). CdSe QDs with different sizes were obtained by controlling their growth time, and the estimated sizes of the CdSe QDs ranged from 2.5 to 5.1 nm. The first excitonic absorption and photoluminescence (PL) peak shifted to lower energy with increasing QD size in the strong confinement regime. The PL spectra included a shoulder peak in the spectra of smaller QDs because of preferential adsorption. A comparison of the empirical trends and experimental results provided a fundamental understanding of the size-dependent properties of the CdSe QDs. In addition, time-resolved PL spectra in conjunction with surface characterization results showed that the PL behavior can be explained by the additional contribution of electron–phonon interaction.