PHOTOELECTROCHEMISTRY IN SEMICONDUCTOR PARTICULATE SYSTEMS .16. PHOTOPHYSICAL AND PHOTOCHEMICAL ASPECTS OF COUPLED SEMICONDUCTORS - CHARGE-TRANSFER PROCESSES IN COLLOIDAL CDS-TIO2 AND CDS-AGI SYSTEMS

The mechanistic and kinetic details of the charge injection from excited CdS into a large bandgap semiconductor such as AgI and TiO2 have been investigated by coupling the two semiconductor systems in the colloidal form. The interaction between the two colloids led to the quenching of CdS emission. The rate constants for the charge injection from excited CdS into the conduction band of AgI and TiO2 colloids were determined to be 2.2 × 107 and >5 × 1010 s-1, respectively. Transmission electron microscopic analysis indicated the possibility of several CdS colloidal particles interacting with a single particle of TiO2 and participating in the charge injection process. Primary photochemical events in the CdS-TiO2 system were investigated by picosecond laser flash photolysis. The charge injected into the TiO2 colloid and trapped at the Ti4+ site was characterized from its broad absorption in the region of 500-760 nm. The extended lifetime of these trapped charge carriers indicated an improved charge separation in the coupled semiconductor system. © 1990 American Chemical Society.