Laser-induced anti-Stokes resonance Raman scattering: Probe for energy transfer inF-center–CN−-molecule defect pairs in CsCl

Optical excitation of the two electronic absorption bands of F-center–${\mathrm{CN}}^{\mathrm{-}}$ defect pairs in CsCl creates a highly efficient electronic to vibrational (e-v) energy transfer process, characterized by rapid nonradiative relaxation of the F electron in contrast to a slowly cascading sequence of fluorescence transitions between the six lowest excited ${\mathrm{CN}}^{\mathrm{-}}$ vibrational states. This behavior allows, by pumping with the same laser beam, to both populate nonequilibrium ${\mathrm{CN}}^{\mathrm{-}}$ vibrational states and to probe their existence and physical properties by anti-Stokes resonance Raman scattering. Experiments with this technique were performed, testing the temperature, wavelength, and intensity dependence of the anti-Stokes Raman spectra and their polarization. Comparison with the earlier vibrational emission results show close agreement for low-${\mathrm{CN}}^{\mathrm{-}}$-doped crystals, but pronounced differences for higher-doped crystals, in which vibrational (v-v) energy transfer from the $F_H$(${\mathrm{CN}}^{\mathrm{-}}$) centers into the free ${\mathrm{CN}}^{\mathrm{-}}$ defect system occurs. These results provide the basis for using pulsed anti-Stokes Raman spectroscopy as a viable probe for our planned time-resolution studies of the e-v and v-v transfer in these systems.