Here we show the results we obtained in the fabrication of planar wave guide lasers based on monoclinic double tungstates doped with Er3+ and Tm3+. We have successfully introduced these ions into the lattice matched KY0.59Gd0.19Lu0.22(WO4)(2) epitaxial layers grown on KY(WO4)(2) substrates without loss of optical quality and keeping a high refractive index contrast between the epitaxial layer and the substrate. We characterized the waveguiding properties of these epitaxial layers at lambda = 632.8 nm by dark modes spectroscopy, and we showed that these waveguides can support several TE and TM modes. Spectroscopic characterization of the active lanthanide ions in these crystals is also presented.