Time-resolved photoluminescence of individual CdS nanowires

We study photoluminescence (PL) dynamics of single VLS-prepared CdS nanowires. AFM imaging reveals that while some nanowires are straight and uniform, the others show significant morphological irregularities. Low temperature PL of uniform nanowires displays a single near band edge (NBE) peak. Spectra of the irregular nanowires exhibit a broad PL band with a high energy shoulder in the same energy range as the NBE peak of the uniform nanowires, as well as an array of narrow peaks at the lower energy. Spatially-resolved PL images indicate that the narrow lines originate at specific locations along the nanowire. Time-resolved PL (TRPL) measurements show that NBE emission in all nanowires is short-lived (lifetime $<$ 50 ps), indicating the presence of non-radiative recombination channels. On the other hand, TRPL of the localized states exhibit are significantly longer (400 ps to 1 ns) and vary from line to line. At room temperature, the PL spectra of all nanowires, regardless of the morphology, consist of the single short-lived NBE emission peak. We acknowledge the support of ACS through the PRF, and NSF through grants 0071797, 0216374, and a graduate fellowship (JLL).