Photon frequency shift in curvature-based Extended Theories of Gravity S. Capozziello, G. Lambiase, A. Stabile and An. Stabile Eur. Phys. J. Plus, 136 3 (2021) 344 Published online: 26 March 2021 DOI: 10.1140/epjp/s13360-021-01322-1