Improvement of the luminescent intensity of Yb/Er: CaF2 nanocrystals by combining Na+-doping and active-core/active-shell structure

Ultrasmall Yb/Er: CaF2 NCs are chosen as an example to certify the UC emission intensity can be greatly enhanced through combining various approaches together, including Na+ ions doping, control shell thickness and tune Yb3+ concentration in the shell. In comparison with Na+-free 20Yb/2Er: CaF2 NCs, the upconversion luminescence of 20Yb/2Er: CaF2@10Yb: CaF2 NCs containing Na+ ions in the core and 10% Yb3+ in the shell with 5 nm thickness intensifies for about 95 times.271