We report on our thorough optical investigations of the Yb pnictide compounds, performed over a large photon-energy spectral range. From Kramers-Kronig analysis we obtain the complete excitation spectrum in terms of the optical dielectric functions. Applying a phenomenological harmonic-oscillator model we extract the unscreened plasma frequency and the resonance frequency of the transverse-optical-phonon mode. Our experimental findings suggest furthermore a d-4f electronic transition at about 0.2 eV, in agreement with high-energy electron-spectroscopy results. We also report on our Raman-effect measurements. Moreover, we compare our results with the reference material ScN and we discuss the influence of nonstoichiometry in the Yb pnictides.