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

Abstract

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.