IR laser ablation was used for the systematic matrix-isolation investigation of reaction products of alkali metal fluorides and fluorine. New insights about periodic trends in the reaction behaviour of alkali metals and the formation as well as the photochemistry of alkali metal trifluorides are presented. New bands were found for the antisymmetric stretches of CsF₃ and [F₃]⁻ in solid krypton and nitrogen, and for the combination bands (νₐₛ + νₛ) of CsF₃ and [F₃]⁻ in solid krypton and argon.