The ternary nitride CaZn2N2, composed only of earth-abundant elements, is a novel semiconductor with a band gap of similar to 1.8 eV. First-principles calculations predict that continuous Mg substitution at the Zn site will change the optical band gap in a wide range from similar to 3.3-1.9 eV for Ca(Mg1-xZnx)(2)N-2 (x = 0-1). In this study, we demonstrate that a solid-state reaction at ambient pressure and a high-pressure synthesis at 5 GPa produce x = 0 and 0.12 and 0.12 < x <= 1 polycrystalline samples, respectively. It is experimentally confirmed that the optical band gap can be continuously tuned from similar to 3.2 to similar to 1.8 eV, a range very close to that predicted by theory. Band to band photoluminescence is observed at room temperature in the ultraviolet red region depending on x. A 2% Na doping at the Ca site of Ca(Mg1-xZnx)(2)N-2 converts its highly resistive state to a p-type conducting state. Particularly, the x = 0.50 sample exhibits intense green emission with a peak at 2.45 eV (506 nm) without any other emission from deep-level defects. These features meet the demands of III-V group nitride and arsenide/phosphide light-emitting semiconductors.