Near-Infrared Light-Induced Photocurrent from a (NaYF4:Yb-Tm)/(Cu2O) Composite Thin Film

Utilization of photons of sub-bandgap energy, mostly near-infrared (NIR) photons, is highly desirable for photovoltaic devices. We show that (NaYF4:Yb-Tm)/(Cu2O) composite films formed by electrodeposition exhibit robust photoactive current generation under NIR light excitation. The composite films consist of homogeneous crystalline particles of the fluoride and Cu2O in sub-micrometer size. From spectroscopic characterization, it is found that the NaYF4:Yb-Tm layer in the composite film converts NIR radiation by up-conversion into visible emission, which is efficiently absorbed by the covering semiconducting Cu2O film, producing photoelectrons. Accordingly, the composite films exhibit highly photoactive current generation by means of a photoelectrochemical process driven by NIR irradiation. The methodology demonstrated here may have certain implications for the utilization of NIR radiation in solar cells, photocatalysts, and infrared photodetectors.