Growth and enhanced upconversion luminescence intensity of Mg2+ and Cr3+ co-doped β-NaYF4:Yb3+/Er3+ microcrystals

In this study, Cr3+ and Mg2+ co-doped beta-NaYF4:Yb3+Er3+ (NYFYE) microcrystals were synthesized for the first time by the facile hydrothermal method. CP3+ and Mg2+ co-doping was confirmed to influence the structure, morphology and UCL property of NYFYE microcrystals. The growth mechanism of NYFYE microcrystals doped with different Cr3+ and Mg2+ was discussed in detail. With 16 mol% Cr3+ and 4 mol% Mg2+ co-doping into NYFYE, the UC emissions were enhanced to 7 times (green) and 4 times (red) higher than those of the undoped counterpart, and the mechanism was explored by considering the different roles of Cr3+ and Mg2+, the surface quenching and concentration quenching effects. This finding suggests the co-doping of two different impurity ions may be a better approach than corresponding single impurity ion doping for morphology control and UCL intensity enhancement, which is instructive for high performance UC crystals design.