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Infrared reflection and Raman spectra of single crystals of 7Li,GA03 and 6Li,Ge03 containing 7.42 and 9.10% of 6Li and 'Li, respectively, are measured and the oscillator parameters ;LO, $TO, y~o ,and y r o determined using the Kurosawa dispersion relation. The experimental attenuated total reflection spectra are in good agreement with the calculated polariton dispersion curves. The resonance type interactions between parent and isotopic impurity deformation modes are interpreted; the behaviour of the corresponding phonons depends on their symmetry species.Les spectres infrarouge et Raman de monocristaux de 'LiGeO, et 6Li,Ge03, contenant 7,42 et 9,10% de 6Li et 'Li, respectivement, ont btB analyses e t les parametres ;LO, ;TO, y~o , et TO de l'oscillateur ont btb determines i partir de la relation de dispersion de Kurosawa. Les spectres obtenus par reflexion totale attbnube sont en bon accord avec les courbes de dispersion du polariton calculbes. Des interactions resonantes ont Ate mises en evidence entre modes de deformation de I'isotope preponderant et de l'impuretb isotopique ; le comportement des phonons correspondants est diffbrent suivant leur type de symbtrie.

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Raman spectra of LiB3O5 and Li2B4O7 crystals have been studied. Raman scattering efficiency and oscillator strengths of some polar vibrations were estimated. Contribution of various vibrations to nonlinear optical coefficients according their assignment has been discussed. Influence of K and Ag impurity ion on Raman spectra of Li2B4O7 have been studied. Anomalies of the isofrequency temperature dependencies of Raman spectral intensity observed at T=235 K are interpreted in terms of the translational structural phase transition.