Yellow upconversion (UC) luminescence is observed in Ho3+/Yb3+ co-doped CaMoO4 synthesized by complex citrate-gel method. Under 980 nm excitation. Ho3+/Yb3+ co-doped CaMoO4 exhibited yellow emission based on green emission near 543 nm generated by F-4(4), S-5(2) -> (5)I8 transition and strong red emission around 656 nm generated by F-5(5) -> I-5(8) transition, which are assigned to the intra 4f transitions of Ho3+ ions. The optimum doping concentration of Ho3+ and Yb3+ was investigated for highest upconversion luminescence. Based on pump power dependence, upconversion mechanism of Ho3+/Yb3+ co-doped CaMoO4 was studied in detail. (c) 2012 Elsevier Ltd. All rights reserved.