Controllable white upconversion luminescence in Ho ³⁺/Tm ³⁺/Yb ³⁺ co-doped CaMoO ₄

The polycrystalline Ho ³⁺/Tm ³⁺/Yb ³⁺ co-doped CaMoO ₄ phosphors were successfully synthesized by complex citrate-gel method. Under the laser excitation of 980 nm, Ho ³⁺/ Tm ³⁺/Yb ³⁺ co-doped CaMoO ₄ shows the bright white upconversion (UC) emission visible to the naked eye, which is composed of a blue emission at 475 nm from Tm ³⁺, and green and red emissions at 543 nm and 651 nm from Ho ³⁺. The coordinates of Ho ³⁺/Tm ³⁺/Yb ³⁺ co-doped CaMoO ₄ in the commission international de'eclairage (CIE) chromaticity diagram can be controlled from a cool to a warm white color depending on the Tm ³⁺ and Ho ³⁺ concentrations. In Ho ³⁺/Tm ³⁺/Yb ³⁺ co-doped CaMoO ₄, the UC luminescent properties on Tm ³⁺ and Ho ³⁺ concentrations and mechanism based on laser pump power were discussed in detail.