Upconversion color tunability and white light generation in Yb3+/Er3+/Tm3+ tri-doped CaF2 single crystals

Yb3+/Er3+/Tm3+ tri-doped CaF2 single crystals have been successfully synthesized via Temperature Gradient Technique (TGT) method, and represented by X-ray diffraction (XRD) examination, absorption and fluorescence spectrum, pump power dependence and lifetime analysis in details. Under the excitation of 980 nm laser diode (LD), the upconversion luminescence (UCL) spectra of Yb3+/Er3+/Tm3+/CaF2 as a function of Tm3+ concentration are made up of intense blue (Tm3+:1G4 → 3H6), green (Er3+: 4S3/2, 2H11/2 → 4I15/2), and red (Er3+:4F9/2 → 4I15/2) emissions, which are located at 478, 523, 539 and 656 nm, respectively. With increasing concentration of Tm, the color can be tunable from orange-yellow, white to blue light. And the optimal Yb3+/Er3+/Tm3+ doping concentrations for white light are determined to be 10%Yb, 0.1%Er and 0.05%Tm. The research indicates that the as-prepared materials may have potential applications in the fields of three dimensional displays, back lighting, white light sources, and so on.