Utilization of photons of sub‐bandgap energy, mostly near‐infrared (NIR) photons, is highly desirable for photovoltaic devices. We show that (NaYF 4 :Yb‐Tm)/(Cu 2 O) 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 Cu 2 O in sub‐micrometer size. From spectroscopic characterization, it is found that the NaYF 4 :Yb‐Tm layer in the composite film converts NIR radiation by up‐conversion into visible emission, which is efficiently absorbed by the covering semiconducting Cu 2 O 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.
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Jia et al. (2014) studied this question.