Highly mismatched alloys (HMAs) are dilute alloys whose fundamental properties are dramatically modified through the substitution of a relatively small fraction (up to ∼5%) of host atoms with a very different element. Specific examples are dilute III–V nitrides (e.g. GaNxAs1−x) and II–VI oxides (e.g. ZnOxTe1−x) in which the conduction bands are strongly modified by the anticrossing interaction between localized states of O or N and the extended states of the semiconductor matrix. Using a highly non-equilibrium method: the combination of ion implantation and pulsed laser melting (II-PLM) we have synthesized a wide variety of III-Nx-V1−x and II-Ox-VI1−x alloys with N or O content up to 2%. The structural and optical properties of these HMAs have been systematically investigated. In particular, we demonstrated that the Zn1−yMnyOxTe1−y dilute oxide is a multiband alloy that can be used for the realization of the single junction, high efficiency intermediate band solar cells.