The role of Pt2+ and Pt4+ impurity ions in the photochemistry of single-crystal silver chloride

Both divalent and tetravalent platinum ions are substitutionally incorporated into silver chloride during the melt growth of single crystals. Pt2+ is believed to occupy sites of octahedral or tetragonal symmetry which are formulated as (PtCl6)4− and { (PtCl6)4−⋅Ag+vac}, respectively. The former complex functions as an electron trap, whereas the charge-compensated center has a significant capture cross section for holes. The predominant products of these reactions, (PtCl6)5− and { (PtCl6)3−⋅nAg+vac}, where n=1 to 3, have been identified by EPR spectroscopy. Pt4+ ions are fully charge compensated in AgCl, and the resultant complex, { (PtCl6)2−⋅3Ag+vac}, is a deep electron trap. The most stable photoproduct from both AgCl‖Pt2+‖ and AgCl‖Pt4+‖ was { (PtCl6)3−⋅2Ag+vac}. The lifetime at room temperature and the trap depth for this complex have been determined.