Studies on Ag⁻ Centers in Alkali Halides. I. Nature of Optical Transitions: KCl

Abstract

A study was made on absorption and emission spectra of Ag⁻ centers in KCl crystals. By inspecting the excitation spectra for emission, two new bands were found at 3.11 and 3.27 eV in addition to the previously known 4.36 eV absorption band. These three bands, named A, B, and C, are ascribed to transitions ¹S₀→³P₁, ³P₂ and ¹P₁ respectively. Besides the 2.93 eV emission, another emission band was discovered at 4.08 eV. They are attributed to transitions ³P₁ and ¹P₁→¹S₀. Energy parameters and electron-lattice coupling constants specifying the configuration-coordinate surfaces were determined from the peak energies, second moments, and Stokes shifts of the observed spectra. Data on the degree of polarization suggest that a trigonal lattice deformation is dominantly realized in each of the relaxed ¹P₁ and ³P₁ states. The shape of the C band and the ratio of life times for the ¹P₁ and ³P₁ states are in reasonable agreement with theory.