  Using high-resolution extreme ultraviolet resonant inelastic X-ray scattering
(EUVRIXS) spectroscopy at Cu M-edge, we observed the doping dependent spectral
shifts of inter-orbital (dd) excitations of YBa_2Cu_3O_(7-x) and
La_(2-x)Sr_xCuO_4. With increasing hole doping level from undoped to optimally
doped superconducting compositions, the leading edge of dd excitations is found
to shift towards lower energy loss in a roughly linear trend that is
irrespective to the cuprate species. The magnitude of energy shift can be
explained by including a 0.15 eV Coulomb attraction between Cu 3d_(x^2-y^2)
electrons and the doped holes on the surrounding oxygens in the atomic
multiplet calculations. The consistent energy shift between distinct cuprate
families suggests that this inter-site Coulomb interaction energy scale is
relatively material-independent, and provides an important reference point for
understanding charge density wave phenomena in the cuprate phase diagram.
