YLiF4 and LuLiF4 single crystals codoped with thulium and holmium were successfully grown by the Czochralski Technique. The segregation coefficients of the dopants in these crystals were measured and the influence of the dopants on the lattice parameters was investigated. The distribution of birefringence along the a-axis was in the order of 10(-1) in each crystal. Laser performance of both YLiF4 and LuLiF4 codoped with thulium and holmium was compared.