Optical Studies of Layered Inorganic Solids: A Novel Phase Transition and Energy Transfer Studies.

The optical properties of a group of dicyanoargentates(1) and dicyanoaurates( 1) have been studied. The samples include K2Na[Ag(CN)2I3, Tb[Ag(CN)2]3, Tb[Au(CN)2I3 and a series of compounds of the form Tb,Lal-,[Ag(CN)2]3 with x=0.001, 0.01 and 0.1. Additionally, a novel type of silver-gold mixed- metal sample (L~[A~,Au~-,(CN)~]~ with x=0.9 and 0.5) was synthesized and characterized. The compound K2Na[Ag(CN)2I3 has earlier been shown to exhibit a phenomenon known as luminescence thermochromism, whereby only one emission band is present at very low temperatures and very high temperatures, but a second, lower energy band is also present at intermediate temperatures. This prompted further investigation to explain this behavior. This investigation revealed the existence of an interesting structural change which is postulated to be an example of a novel type of phase transition, but did not explain the luminescence thermochromism. Further study, including luminescence lifetime results, was necessary to form a model involving energy transfer at lower temperatures and back-energy transfer at higher temperatures. These dicyanoaurates(1) and dicyanoargentates(1) were also studied in the context of energy transfer from the M(CN), donor ion to Tb3+ acceptor ions. The energy transfer is found to follow the Dexter exchange mechanism by a process of elimination of other possible mechanisms. The energy transfer is found to be more efficient in the case of the dicyanoargentate(1) donor than in the case of the dicyanoaurate(1) donor as the spectral overlap between donor and acceptor is greater. The mixed-metal samples display an anomalously strong luminescence at ambient temperatures that cannot be explained by the optical results alone. This luminescence is also strongly tunable in that changing physical parameters such as temperature, excitation wavelength or Ag/Au ratio results in changes in the emission energy of the sample. Results are presented which support the use of mixed-metal systems as tunable donors for energy transfer studies