Near-Infrared Light-Induced Photoresponse in Er 3+ /Li + -Codoped Y 2 O 3 /Poly(methyl methacrylate) Composite Film.

We demonstrate Li + -doping engineering for improving the near-infrared (NIR) photoresponse in an Er 3+ -activated Y 2 O 3 phosphor. We show that the rational incorporation of Li + results in a large enhancement of the upconversion (UC) emission intensity up to 29 times upon excitation of NIR light. The improved UC properties could be associated with the enhanced dipole-dipole transition probability due to Li + -induced changes in the local site symmetry for Er 3+ ions and improvement in the crystallinity of the samples. We further demonstrate the construction of UC phosphor/polymer composite films by attaching the UC phosphor/polymer composite film onto a Si-photoresistor. The device shows a large enhancement of the photovoltage response from 0.16 to 0.4 V in Li-doped samples under NIR light illumination. These results suggest an effective doping strategy for the improvement of the UC performance of the oxide phosphor and its wide applications in solar energy utilization and NIR response devices.