This study explores comprehensively the carrier dynamics in ZnSeO and ZnTeO using photoluminescence (PL) and time-resolved PL spectroscopy. As the O concentration increases, the PL emissions shift toward lower energies. Additionally, the PL lifetime increases with increasing O contents and the decay curves exhibit complex behavior. In the case of ZnSeO, the mechanism of carrier recombination undergoes a complicated change from trapped to free excitons with the increase in temperature. The incorporation of O in ZnTe generates a wide distribution of electron localization below the energy of the E- conduction subband, and these cause broad PL emission and serve as another intermediate band. Electrons in both the E+ and the E- conduction subbands favor rapid relaxation to low energy states. Moreover, temperature-independent long carrier lifetimes (> 130.0 ns) that are induced by localized electrons increase with O concentration.