Characterization of SrTiO3 target doped with Co ions, SrCoxTi1−xO3−δ, and their thin films prepared by pulsed laser ablation (PLA) in water for visible light response

•Charge-transfer reactions among Co2+, Ti3+, O2− and Sr2+ species on Ar+-sputtered SrCoxTi1−xO3−δ targets are detected.•PLA of the low Co loading targets in water yields nanoparticles of crystalline SrCo0.3Ti0.7O3−δ core covered with amorphous SrTiO3.•PLA thin films appear catalytic photo-degradation activities of dye molecules under very weak 470nm.•The activity enhancement by Co ions is studied with respect to the d-d transition and the charge-transfer between Co ions and Oxygen.