Selectively enhanced green upconversion (UC) and near-infrared (NIR) downconversion (DC) emissions of Er3+ by Yb3+-Mn2+ dimer sensitizing have been demonstrated in Er3+/Yb3+/Mn2+ tri-doped spinel MgGa2O4 upon excitation of 980 nm laser diode (LD). By optimizing the doping rate of Mn2+, the intensity ratio of green to red UC emission intensities of Er3+ (G/R) could be enhanced about 10 times. Meanwhile, the 1.5 mu m NIR DC emission could also be increased about 3.6 times in this system. The DC and UC emission properties, UC mechanism, as well as the enhancing mechanism have been investigated and discussed in detail. A selectively enhancing mechanism based on Yb3+-Mn2+ dimer sensitizing is proposed to explain the selectively enhancing phenomena. This work could inspire the design of novel UC materials for various applications, such as temperature sensors and optical transmission, etc. (C) 2015 Elsevier Ltd. All rights reserved.