Physikalisches Institut der Universität Münster, 44, Münster, W. Germany
Abstract:
The emission spectra and lifetimes of the Au— center in KCl crystals were measured. The Au— concentration was measured by counting the activity of a radioactive tagged sample to determine the oscillator strength of the electronic transitions. The lifetime of the A'emission is calculated from the oscillator strength and is close to the experimental value of 103 ns at 4 K. The lifetimes and intensities of the Au— emission bands C', B', A' and were measured between 4 and 500 K. The A'emission consists of a fast and slow decaying component. Time-resolved emission spectroscopy improved the measurements of the emission. From the temperature dependence of the lifetimes and intensities it is found that the radiating states of the A' and emission 3T1u and 3A1u are coupled by radiationless transitions. These transitions and the radiationless transitions from the excited state of the B' emission must be described as transitions between weakly coupled states similar to the radiationless transitions in rare earth ions. The excited state of an absorption band at 236 nm is responsible for the C' emission. Both the C' emission and the 236 nm absorption are phonon-induced transitions. The most probable explanation for the C' excited state is that the C' as well as the B' excited states come from the atomic state 3P2 which is split into 3T2u and 3Eu by the crystal field. The splitting energy is 0.9 eV and implies that one should look for the same effect in other s2 centers.