[en] The solid-state absorption spectra of Cf(III) ions as a dopant in lanthanide trihalide hosts (LnCl₃: Ln = Ce, Sm, and Y; LnBr₃: Ln = Ce, Sm, Tb, and Y; LnI₃: Ln = Ce and Y) have been recorded. The spectra of Cf(III) have been correlated with the various crystal structures. The phonon Raman spectra and solid-state absorption spectra of PmF₃, PmCl₃, PmBr₃, and two crystal modifications of PmI₃ have been recorded. Symmetry assignments have been made for the Raman-active bands for these trihalides and also the sesquioxide. The room-temperature absorption spectra have been correlated to crystal field effects. The symmetry assignments of the Raman-active phonon modes have been made based on polarized Raman spectra from single crystals of YF₃-type orthorhombic TbF₃ and PuBr₃-type orthorhombic NdBr₃. Raman spectra of other isostructural lanthanide compounds have been recorded and compared. Symmetry assignments for these compounds have been made by analogy to the single-crystal assignments. Raman spectra have been obtained and catalogued for a number of actinide compounds. Symmetry assignments have been made for the observed Raman-active phonon bands in this work based on the assignments made for isostructural lanthanide compounds. 29 figs., 22 tabs