Dr. Marc Leblans Department Physics University of Antwerp
4 PM, Thursday, October 26, 1995
Room 101, Olin Physical Laboratory
In most alkali halides the F center (an electron trapped in an anion vacancy) exhibits a very efficient electronic luminescence after optical excitation. This luminescence is (partially) quenched when the F center is perturbed by a molecular impurity (such as CN- and OH-), due to electronic-vibrational (E-V) energy transfer to the stretch vibration of the impurity. The phenomenon is relatively difficult to study for F-center--OH- defect pairs: In contrast to the case of F-center--CN- pairs, no vibrational emission and no residual electronic luminescence is observed for the F-center--OH- pair, and both electronic and vibrational relaxation take place on a much faster time scale. Results on the nonradiative electronic relaxation of the F-center--OH- defect pair, obtained with a sub-picosecond pump-probe laser technique, will be discussed. The E-V energy-transfer process and the vibrational relaxation of the OH- impurity is studied by means of Stokes and Anti-Stokes resonant Raman scattering.