The composition and temperature dependence of the Raman spectra of molten LnI3-CsI (Ln = Ce, Dy, Ho) mixtures have been measured. Raman spectra of the polycrystalline compounds CeI3, DyI3, Cs3CeI6, Cs3DyI6 and Cs3Dy2I9 have also been measured from room temperature up to ∼ 750 ◦C, where melting occurs for most of these salts. The data are correlated to previous studies involving rare-earth chlorides and bromides and are discussed in terms of the melt structure and the structural systematics of the rare-earth iodide-alkali iodide molten mixtures