We tested a number of fluorescent compounds to be used in luminescent planar concentrators. The two aspects of particular interest are the determination of the excitation and and emission spectra, and the long-term stability of the various compounds, which then in turn determine the short-term and the long-term efficiency of the solar panels. We tested various organic dyes dissolved in a plastic support (polymethylmethacrylate), organic dyes dissolved in simple solvents (water, methanol, ethanol and propanol-2) and luminescent inorganic ions incorporated in various glasses. We also carried out the direct determination of the efficiency of actual solar panels coupled to silicon photovoltaic strips. In this paper we present the results of these measurements. Although the organic dyes incorporated in a plastic base offer the best short-term performance, their long-term stability has to be improved.