The upconversion properties of β-NaYF4:Yb3+(10%),Er3+(1%) microprisms under different excitation conditions

The upconversion (UC) properties of β-NaYF4:Yb3+(10%),Er3+(1%) microprisms synthesized using a hydrothermal method were studied under different excitation conditions. It was found that the UC emission of β-NaYF4:Yb3+(10%),Er3+(1%) was more sensitive to the 980 nm photons than the 1560 nm photons, because of the high mole ratio of Yb3+/Er3+ in crystals. Applying this material at the back of a hydrogenated amorphous silicon (a-Si:H) solar cell, a short-circuit current density of 64 μA/cm2 was measured under 0.53 W/cm2 980 nm laser excitation. This corresponds to an external quantum efficiency of 0.015% of the solar cell. When co-excited with the 980 nm and 1560 nm lasers, a very weak enhancement in the current was shown, which resulted from the slightly increased red emission. This indicates that co-excitation with multiple wavelengths accessible to the β-NaYF4:Yb3+(10%),Er3+(1%) microprisms is not an effective method to enhance the efficiency of a-Si:H solar cells.