Structure and optical properties of In_1-xRE_xTaO₄ (RE= Er, Yb) and their oxynitrides, an evaluation as photocatalysts for water splitting

Ta₂O₅ based photocatalysts show a band gap of about 4.0 eV, this implies that they should be used under UV electromagnetic radiation, this condition limits its applications. Zou, Z. et al. [1] prepared visible-light active photocatalyst with formula InTaO₄:NiO, with a wolframite structure and a band gap of 2.6 eV; more recently this system was reviewed by Malingowsky, A. et al. [2] and they found a direct band gap of 3.96 eV for the nickel doped InTaO₄ compound. In this work, we studied the In_1-xRE_xTaO₄ (RE= Er, Yb, 0.0≤x≤2.0) solid solution with a wolframite structure and we found that for the Yb case the system it does not exhibit absorption in the visible region of the electromagnetic spectrum, while the Er system it shows a rich absorbance spectrum in the visible region. Probably this absorbance signals are associated to internal f-f electronic transitions and could be active in photocatalysis under visible radiation.

[1] Z. Zou, J. Ye, K. Sayama, H. Arakawa, Nature. 414 (2001) 625–627.
[2] A.C. Malingowski, P.W. Stephens, A. Huq, Q. Huang, S. Khalid, P.G. Khalifah, Inorg. Chem. 51 (2012) 6096–6103