Time, illumination and solvent dependent stability of cadmium sulfide nanoparticle suspensions

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 4. months, 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.