Increasing Doping Solubility of RE3+ Ions in Fergusonite BiVO4 via Pressure-Induced Phase Transition

Eu3+ ions doped bismuth vanadate powders were synthesized by a hydrothermal method, and the effect of Eu3+ ions doping on the crystal structure was investigated by X-ray diffraction (XRD), Raman, and UV-vis diffuse reflectance spectra. XRD and Raman results reveal that the doping solubility of Eu3+ ions in fergusonite-BiVO4 is extremely small. Above 0.5 mol % doping, a structural transition from fergusonite to zircon structure occurs. This phase transition results in band gap enhancement and thus limits its photocatalytic performance. Upon compression, zircon-BiVO4:Eu3+ is not stable, and a zircon-to-scheelite transition presents above 5 GPa. It is noted that this transition is irreversible, and the high-pressure scheelite structure transforms back to the fergusonite structure rather than the original zircon structure after pressure release. The transition sequence of zircon-to-scheelite-to-fergusonite in a compression-decompression cycle for BiVO4:Eu3+ provides one method to synthesize fergusonite-BiVO4:Eu3+ with more doping content. This result confirms that pressure is one effective strategy to access new structures and novel physical properties of functional material.