Ion-redistribution induced efficient upconversion in β-NaYF_4:20%Yb^3+,2%Er^3+ microcrystals with well controlled morphology and size

We develop an efficient green upconversion (UC) β-NaYF4:20%Yb3+,2%Er3+ microcrystal with well controlled morphology and size by hydrothermal method using two different chelating agents of CIT and EDTA-2Na via a simple ion-exchange reaction. Importantly, the UC emission efficiency of newly developed CIT and EDTA-2Na β-NaYF4:20%Yb3+,2%Er3+ microcrystals is almost as strong as that of commercial counterpart by solid-state method. A proof-of-concept β-NaYF4:20%Yb3+,2%Er3+ microcrystal waveguide is demonstrated to extend their applications in modern micro-optoelectronics. The local ion-redistribution process during the ion-exchange reaction, which effectively disperses the locally clustered Yb3+, accounts for the enormously enhanced UC emission in β-NaYF4:20%Yb3+,2%Er3+ microcrystals.