Yb3+/Er3+ concentration dependent microstructure evolution and green/red emissions of NaYF4:Yb/Er phosphors

Photon upconversion is promising for applications such as data storage, drug delivery and solar cells. beta-NaYF4:Yb/Er samples were synthesized by a facile hydrothermal method. The effects of Yb/Er ratio on the microstructures, morphology evolution and luminescence properties were studied. The SEM results showed that the morphology of the samples evolved gradually from plate to prismatic structure with an increase in Yb3+ concentration. This indicates that the growth rate along the c-axis crystal planes of NaYbF4 lattices is more rapid than NaYF4 lattices. Photoluminescence measurements demonstrate that the bright multicolored upconversion emissions can be fine-tuned from green to red by adjusting the codoped Yb/Er ratio under 980 nm laser excitation. The tunable emission is due to the energy back transfer from Yb3+ to Er3+. Applying this material in perovskite solar cell, a current density of 4 mu A cm(-2) is obtained under 40 mW and 980 nm laser excitation.