| Scope and Method of Study. Time-resolved site-selection spectroscopy is utilized to study spectral energy migration between Eu('2+) ions in RbMgF(,3):Euk('2+),Mn('2+) crystal. Degenerate four-wave mixing (FWM) transient-grating spectroscopy is employed to study certain nonlinear processes in alexandrite (BeAl(,2)O(,4):Cr('3+)) crystal. Exciton diffusion is investigated in NdP(,5)O(,14) by nondegenerate FWM transient-grating spectroscopy.;Findings and Conclusions. In RbMgF(,3):Eu('2+), Mn('2+) crystal, the results indicate that the transfer process between Eu('2+) ions in three nonequivalent sites is consistent with electric dipole-dipole interaction and is enhanced by the thermal occupation of the upper crystal field component of the sensitizer. The microscopic origin of the different types of sites may be due to the presence of structural or chemical impurities in the lattice. The results imply that Eu('2+) ions are forming clusters in this host. The FWM signal efficiency in alexandrite varies quadratically with pump power for large pump beam crossing angles with some saturation at small angles. When the pump beams are polarized parallel to the b-, c-, and a- axis of the crystal strong, relatively weak, and no FWM signals are obtained, respectively. Surface data show significant deviations from quadratic behavior and saturation effects. The results show that FWM signals are due mainly to scattering from a phase grating. At low temperature, the exciton diffusion in NdP(,5)O(,14) is due to electric dipole-dipole interactions. The diffusion coefficient is proportional to the concentration of Nd('3+) ions raised to four thirds power the transitions of which are in resonance with the laser excitation wavelength. This rules out the possibility of having a mobility edge in this crystal in the study per se. |
