ABSTRACT
Intrinsic defects such as vacancies, interstitials, and anti-sites often introduce rich luminescent properties in II-VI semiconductor nanomaterials. A clear understanding of the dynamics of the defect-related excitons is particularly important for the design and optimization of nanoscale optoelectronic devices. In this paper, low-temperature steady-state and time-resolved photoluminescence (PL) spectroscopies have been carried out to investigate the emission of cadmium sulfide (CdS) nanobelts that originates from the radiative recombination of excitons bound to neutral donors (I(2)) and the spatially localized donor-acceptor pairs (DAP), in which the assignment is supported by first principle calculations. Our results verify that the shallow donors in CdS are contributed by sulfur vacancies while the acceptors are contributed by cadmium vacancies. At high excitation intensities, the DAP emission saturates and the PL is dominated by I(2) emission. Beyond a threshold power of approximately 5 µW, amplified spontaneous emission (ASE) of I(2) occurs. Further analysis shows that these intrinsic defects created long-lived (spin triplet) DAP trap states due to spin-polarized Cd vacancies which become saturated at intense carrier excitations.
Subject(s)
Cadmium Compounds/chemistry , Nanostructures/chemistry , Nanostructures/ultrastructure , Selenium Compounds/chemistry , Electron Transport , Particle SizeABSTRACT
A technique utilizing the capillary assisted sieving capability of carbon nanotubes (CNTs) to achieve fractionation of nanoparticles of small size distribution is presented. By dipping aligned CNT arrays into a solution comprising different sized quantum dots (QDs), size-selective gradient decoration of QDs onto CNTs is achieved. The fractionating capability of CNTs is also demonstrated for poly-dispersed manganese doped zinc sulfide nanoparticles and QDs of varying sizes and chemical compositions, which we attribute to the size-selective sieving effect of CNTs. By controlling the terminating point for the flow of QDs across the CNT array, a QD size specific CNT/QD hybrid structure is achieved.
