The optical properties of Yb3+ and Er3+ co-doped Ln2BaZnO5 (Ln = Y or Gd), synthesized by solid-state reaction, are investigated in detail. Two main emission bands centered around 548 nm (green) and 673 nm (red) are observed under 977 nm laser excitation via an upconversion process. Studies of the behavior as a function of dopant concentration are described and relatively high infrared to visible upconversion efficiencies of ∼5% are obtained at room temperature. Under modulated 977 nm excitation and for fixed dopant concentrations, the upconverted emission chromaticity can be varied by changing the excitation duration. The results of power dependence studies and lifetime measurements are presented. This detailed study of the upconversion processes allows us to identify the dominant upconversion mechanisms in Yb3+,Er3+ co-doped Ln 2BaZnO5 oxides.