Cooperative luminescence mediated near infrared photocatalysis of CaF₂:Yb@BiVO₄ composites

It is a challenge to develop efficient photocatalyst that can be activated by photons with long wavelength. In our previous work, a near infrared (NIR) driven photocatalyst (e.g., NaYF₄:Yb,Tm@TiO₂) was designed, for which, however, a two-step energy transfer was involved for photocatalysis so that the ultimate photocatalytic capability is low. In this work, we designed and prepared a new type of NIR photocatalyst composed of cooperative luminescence agent CaF₂:Yb and semiconductor BiVO₄, in which a one-step energy transfer occurs to realize NIR photocatalysis. Steady-state and dynamic fluorescence spectroscopy analysis revealed that cooperative energy transfer of a Yb³⁺-dimer to BiVO₄ leads to the indirect excitation of semiconductor BiVO₄ by NIR light. The degradation of methylene blue (MB) compound by CaF₂:1%Yb³⁺@BiVO₄ particles upon NIR radiation and its corresponding controlled experiments demonstrated the NIR light responsive photocatalytic capability. It is noteworthy that nearly 80% degradation ratio of MB was achieved with 7 h of NIR light irradiation, indicating a relatively high photocatalytic activity, compared with that of our previously reported system NaYF₄:Yb,Tm@TiO₂, for which ∼65% of degradation ratio of MB was obtained within 14 h of NIR irradiation. Recycling experiments of photocatalysis indicate that our present CaF₂:Yb@BiVO₄ composite has good photochemical stability in spite of a long time of NIR irradiation.