Controllable white upconversion luminescence in Ho3+/Tm3+/Yb3+ co-doped CaMoO4

The polycrystalline Ho3+/Tm3+/Yb3+ co-doped CaMoO4 phosphors were successfully synthesized by complex citrate-gel method. Under the laser excitation of 980 nm, Ho3+/Tm3+/Yb3+ co-doped CaMoO4 shows the bright white upconversion (UC) emission visible to the naked eye, which is composed of a blue emission at 475 nm from Tm3+, and green and red emissions at 543 nm and 651 nm from Ho3+. The coordinates of Ho3+/Tm3+/Yb3+ co-doped CaMoO4 in the commission international de'eclairage (CIE) chromaticity diagram can be controlled from a cool to a warm white color depending on the Tm3+ and Ho3+ concentrations. In Ho3+/Tm3+/Yb3+ co-doped CaMoO4, the UC luminescent properties on Tm3+ and Ho3+ concentrations and mechanism based on laser pump power were discussed in detail.