Luminescence emission and excitation spectra of thin films composed of SrS:Eu2+ and SrGa2S4:Eu2+ are measured and discussed. The coexistence of the two compounds in the same sample gives the opportunity to compare the energy of the fundamental absorption of SrS and SrGa2S4 in the excitation spectra for the Eu2+ emission in both host matrixes. This work provides experimental evidence that the bandgap energy of SrS is 0.2 eV higher than that of SrGa2S4. From data given in the literature for SrS, the bandgap energy of polycrystalline SrGa2S4 was evaluated at similar to 4.2 eV at 300 K.