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Hypothesis The optical properties of cadmium sulfide (CdS) nanoparticles in suspension are affected by morphology and suspending solvent. Time dependent stability of these properties is solvent dependent and is affected by illumination conditions under which the suspension is stored. Moreover, minute amounts of dissolved oxygen are sufficient in order to facilitate photodegradation. Experiments CdS nanoparticles were synthesized with various shapes using a single precursor, single surfactant route. Thereafter, their optical properties were measured from chloroform and toluene suspensions following periods of up to 4months, under illumination conditions, which included dark storage, visible light and UV irradiation. Findings The changes in optical properties, best shown by the photoluminescence (PL), reveal an intricate behavior, which is dependent upon both the chemical environment and illumination conditions. This is mainly manifested in two ways: the first is an initial intensification of the PL, while later on gradual degradation of the particles and their optical activity are observed. Moreover, a distinct variation of surface state emission was demonstrated for each solvent. Additionally, a solvent dependent variation of the final photodegraded state was observed. Based on these observations, we describe the photodegradation route for CdS nanoparticles in chloroform suspensions. [ABSTRACT FROM AUTHOR]

We synthesized PbS core-CdS arm nanomultipod heterostructures (NMHs) that exhibit PbS{111}/CdS{0002} epitaxial relations. The PbS-CdS interface is chemically sharp as determined by aberration corrected transmission electron microscopy (TEM) and compared to density functional theory (DFT) calculations. Ensemble fluorescence measurements show quenching of the optical signal from the CdS arms indicating charge separation due to the heterojunction with PbS. A finite-element three-dimensional (3D) calculation of the Poisson equation shows a type-I heterojunction, which would prevent recombination in the CdS arm after optical excitation. To examine charge redistribution, we used off-axis electron holography (OAEH) in the TEM to map the electrostatic potential across an individual heterojunction. Indeed, a built-in potential of 500 mV is estimated across the junction, though as opposed to the thermal equilibrium calculations significant accumulation of positive charge at the CdS side of the interface is detected. We conclude that the NMH multipod geometry prevents efficient removal of generated charge carriers by the high energy electrons of the TEM. Simulations of generated electron-hole pairs in the insulated CdS arm of the NMH indeed show charge accumulation in agreement with the experimental measurements. Thus, we show that OAEH can be used as a complementary methodology to ensemble measurements by mapping the charge distribution in single NMHs with complex geometries. [ABSTRACT FROM AUTHOR]