Intense Single Red Emission Induced by Near‐Infrared Irradiation Using a Narrow Bandgap Oxide BiVO 4 as the Host for Yb 3+ and Tm 3+ Ions

As a new way of producing a single red emission under near‐infrared (NIR) irradiation, the possibility of using a narrow bandgap oxide as the host for the sensitizer Yb 3+ ion as well as a suitable activator ion such as Ho 3+ , Er 3+ , or Tm 3+ is considered, because the host can absorb the emissions of the activator ion higher in energy than the red emission. To verify this new concept, BiVO 4 :Yb 3+ ,Tm 3+ using a sol–gel method is prepared and its photoluminescence properties are characterized. BiVO 4 has the bandgap of ≈2.4 eV so that, under NIR irradiation, it absorbs the blue and other higher‐energy emissions of Tm 3+ . As a consequence, BiVO 4 :Yb 3+ ,Tm 3+ exhibits an intense single red emission under the NIR irradiation. The high‐energy emissions absorbed by the host generate electron–hole pairs in the host, so that BiVO 4 :Yb 3+ ,Tm 3+ acts as a photocatalyst under NIR irradiation although the host alone cannot absorb the NIR light. NIR‐induced upconversion luminescence (UCL) and photocatalysis in the region of red lights can be achieved by employing a semiconducting oxide as the host for sensitizer and activator lanthanide ions.