Intermolecular Interactions and Luminescence Spectroscopy of Twodimensional Layered Solids

Abstract

Salts of AAu(CN)₂ (A=K⁺, CS⁺, Tetrabutylammonium⁺) in the solid state form a two-dimensional layered structure. When the cation or the temperature is changed, the nearest neighbor Au-Au distance varies. We have done spectroscopic experiments to probe the dependence of the photophysical properties of these systems on the interactions between Au atoms in two-dimensions. Laser excited emission polarization studies and lifetime measurements have been made on the pure solids and on mixed alkali halide crystals as a function of cation, temperature and host lattice. Low temperature lifetime studies for CsAu(CN)₂ reveal the presence of emitting states separated by 50 cm^-1 with spin-orbital coupling responsible for the closely separated emitting states as in the one-dimensional AnPt(CN)₄.XH₂O systems. Variable temperature polarized emission and crystallographic measurements for KAu(CN)₂ reveal that the observed emission energy varies as R^-3 in agreement with simple exciton theory. Comparisons can be made between intermolecular interactions and luminescence for the two-dimensional AAu(CN)₂ versus the one-dimensional A_nPt(CN)₄ XH₂O systems.