We have studied the luminescence of CuCl and CuBr at low temperatures under the excitation of the second harmonic of the light of a ruby laser (by single photon absorption). We have recorded the whole luminescence spectrum of CuCl and CuBr. In both cases, we have observed a new intense emission line, and have measured the intensity variation of this new line and of the free exciton recombination line versus the intensity of the excitation light. The new emission line has been tentatively explained as due to the recombination of an excitonic molecule. Its position in the spectrum agrees quite well with Sharma's and Wehner's calculation of the binding energy of such a molecule. Its intensity variation can be explained by Knox and Nikitine's theory of the kinetics of the excitonic molecule formation.