Room-temperature green to orange color-tunable upconversion luminescence from Yb3+/Mn2+ co-doped CaO

Room-temperature green to orange color-tunable upconversion (UC) luminescence has been achieved from Yb3+/Mn2+ co-doped CaO by adjusting the doping concentration of Mn2+ ions and the temperature of the samples upon 980 nm laser diode excitation. In this material system, the green UC emission band centered at 508 nm and the wavelength-tunable orange UC emission band from 560 to 725 nm are realized at 980 nm excitation, which originate from the cooperative luminescence of Yb3+ pairs and the |2F7/2, 4T1(4G)〉 → |2F7/2, 6A1(S)〉 transition of exchange-coupled Yb3+–Mn2+ dimers, respectively. The characteristic Stokes and UC emission properties, UC luminescence decay behaviors, temperature-dependent UC emission properties, as well as the involved UC mechanism of CaO:Yb3+,Mn2+ are investigated and discussed in detail. This study offers a new method to design novel UC materials for lighting and display applications instead of using conventionally investigated lanthanide (Ln3+) ions, such as Er3+, Tm3+ and Ho3+.