Spectroscopic and computational studies of [OsCl5(NO)]3- and [RuCl5(NO)]3- donors in AgCl

Information about the structure and performance of two metal nitrosyl dopant complexes in irradiated silver chloride powders has been obtained. Experiment and theory suggest that both [OsCl5(NO)](2-) and [RuCl5(NO)](2-) are incorporated substitutionally into AgCl with their ligands intact. Charge compensation is provided by three proximal silver ion vacancies (=V). Optimal geometries for the resultant [MCl5(NO)](2-). 3V centers (M=Ru or Os) have been determined by calculation, with the configuration (011)(0 (1) over bar 1)(002) being slightly preferred for both metals. The incorporation of these nitrosyls into AgCl introduces midgap vacant levels so that they function as ionized donor centers. Electron trapping results in a series of structural relaxations involving both the dopant and the lattice. The initial deep donor centers produced by trapping are overcompensated structures, [MCl5(NO)](3-). 3V. These centers have been studied by electron paramagnetic resonance spectroscopy at 9, 35, and 94 GHz, and by electron-nuclear double resonance spectroscopy at 9 GHz. Secondary deep donor centers with the formula [MCl5(NO)](3-). 2V result from vacancy diffusion at 120-140 K. Kinetic experiments show that [OsCl5(NO)](3-). 2V centers decay with an effective lifetime of about 550 s at 300 K, although it takes more than 4 x 10(4) s to completely bleach these donors at this temperature. The ruthenium complex has proved to be even more stable. Results described in this paper emphasize the importance of charge compensation and structural relaxations in dopant-related carrier trapping processes. [S0163-1829(99)06013-0].