Photochemistry and Radiation Chemistry of Colloidal Semiconductors 34. Properties of Q‐PbS

Abstract

AbstractPrecipitation of lead ions by hydrogen sulfide in the presence of poly(vinyl alcohol) in aqueous or methanolic solution yields Q‐PbS particles (quantized particles) which have a structured absorption spectrum. The particles have a rod‐like or spherical shape (size quantization mainly in two or three dimensions, respectively). PbS with a structured absorption can also be made in acetonitrile using poly(ethylene oxide) as stabilizer. PbS stabilized by sodium polyphosphate has a structureless absorption spectrum. — Depending on the method of preparation and surface modification after preparation PbS samples fluorescing in the red or/and infrared are obtained. Methyl viologen generally quenches but can in certain cases promote the fluorescence when it is present in low concentration. Oxygen quenches when the colloid is stabilized by polyphosphate. — The rate of the photoanodic dissolution in the presence of air is increased by methyl viologen. Half reduced methyl viologen does not transfer an electron to Q‐PbS but can do so in the case of larger particles. — Illumination under argon leads to increased Ostwald ripening of the particles. However, when sulfite is present in the deaerated solution, photoanodic dissolution takes place. — Attack by hydroxyl radicals generated radiolytically leads to Pb2+ + SO2−4. The fluorescence of a Q‐PbS particle is efficiently decreased after the attack by a single OH radical (i.e. after injection of one positive hole). — Single electron transfer from 1‐hydroxy methyl ethyl radicals, (CH3)2COH, to Q‐PbS also leads to a decrease in fluorescence. These effects are attributed to interactions of the charge carriers deposited by the radicals on the colloidal particles with the exitonic state produced by light absorption. — Accumulated electron transfer to PbS‐particles from organic radicals yields lead metal and organic sulfur compounds. In the beginning of this process, the fluorescence strongly increases (10% quantum yield) which is explained by destruction of surface defect states.