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 dopan t complexes in irradiated silver chloride powders has been obtained. Experi ment and theory suggest that both [OsCl5(NO)](2-) and [RuCl5(NO)](2-) are i ncorporated substitutionally into AgCl with their ligands intact. Charge co mpensation 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 the se nitrosyls into AgCl introduces midgap vacant levels so that they functio n as ionized donor centers. Electron trapping results in a series of struct ural relaxations involving both the dopant and the lattice. The initial dee p donor centers produced by trapping are overcompensated structures, [MCl5( NO)](3-). 3V. These centers have been studied by electron paramagnetic reso nance spectroscopy at 9, 35, and 94 GHz, and by electron-nuclear double res onance spectroscopy at 9 GHz. Secondary deep donor centers with the formula [MCl5(NO)](3-). 2V result from vacancy diffusion at 120-140 K. Kinetic exp eriments show that [OsCl5(NO)](3-). 2V centers decay with an effective life time of about 550 s at 300 K, although it takes more than 4 x 10(4) s to co mpletely bleach these donors at this temperature. The ruthenium complex has proved to be even more stable. Results described in this paper emphasize t he importance of charge compensation and structural relaxations in dopant-r elated carrier trapping processes. [S0163-1829(99)06013-0].