[en] Amorphous erbium-doped silicon oxide (Si_yO_1-y:Er, y≥1/3) thin films are currently under investigation as a luminescent material system for complementary metal-oxide semiconductor compatible light emitters. We have grown films with y≅1/3 and investigated their properties using both positron annihilation and photoluminescence (PL) spectroscopies. Films were characterized ''as deposited,'' following irradiation with 1 MeV Si⁺ ions and after isochronal annealing. The PL yield from both Er³⁺ ions and sensitizing defects is reduced by irradiation, depending strongly on the irradiation fluence and reaching saturation at ∼4x10¹³ Si⁺/cm². Higher implantation fluences result in an open-volume defect structure in the film that persists after annealing. This annealing behavior is similar to that of an unrecoverable quenching effect on Er³⁺-related PL near 1540 nm, and we suggest that these open-volume defects may cause a decoupling of the Er³⁺ ions from sensitizing oxide point defects that form as a result of the film deposition process