Electron-lattice interaction of Ag− and Cu− centers in alkali halides
Absorption, emission, and excitation spectra of Ag− centers in KCl, RbCl, CsCl, and CsBr are measured at low temperatures. The positions of theA emission bands are slightly different afterC andA band excitation, respectively. This is believed to be due to the existence of two different types of minima in the adiabatic potential energy surface of the3T1u state.The symmetry of the energy minima in the1T1u state is trigonal for KCl∶Ag− and Cu−, but tetragonal for CsBr∶Ag−. This becomes evident from the polarization properties of the emission. The energy and temperature dependence of the polarization is discussed.Uniaxial stress causes polarized emission of Ag− and Cu− centers measured from LHeT to 100 K. This is due to a splitting and mixing of the relaxed excited states by the stress. The effects are used to calculate the coupling constants between thep electron and theEg andT2g lattice modes. They are compared with predictions from the point-charge model for different lattice structures.A new assignment of the absorption bands of KCl∶Cu− to the excited states of Cu− is established on measurements of emission spectra and lifetimes.