An intracage geminate CO ... O van der Waals pair is generated through vacuum ultraviolet (VUV) photolysis of 0.1% CO2 in Ar matrices at 18 K. Excitation of CO between 157 and 130 nm (A(1) Pi<--X(1) Sigma(+) vibronic transitions) results in a strong emission due to the S-1-->D-1 transition of O at 560 nm and weak emission bands due to CO and O-2. The band at 560 nm is absent in the emission spectra measured from CO in Ar (1:1000) or O-2 and CO in Ar (1:1:1000) matrices. The observed phenomenon is due to photochemically induced electronic-to-electronic energy transfer. Excited CO and ground-state O(P-3) undergo chemical recombination to result in excited CO2, which dissociates to ground-state CO (X(1) Sigma(+)) and excited O(S-1). Other possible pathways are also discussed but shown to be inappropriate.