Tunable W⁵⁺ Absorbance in Laser Floating Zone Grown Bismuth Tungstate

Bi₂WO₆ has been actively investigated as a viable photocatalysis substitute for TiO₂. This along with progress in designing qubit hosts using W⁵⁺ centers encourages the development of single crystal growths of this material using the floating zone technique. Single crystals of Bi₂WO_6-x were grown using a laser diode floating zone furnace. Laue diffraction and single crystal X-ray diffraction confirm development of single crystalline domains. Williamson-Hall analysis shows annealed floating zone crystals contain less strain compared to unannealed and flux grown samples. Fitting of the heat capacity data shows two optical phonon modes modeled by Einstein oscillators, with the lower energy oscillator decreasing post annealing. The band gap is estimated as 2.6 eV using hyperspectral imaging, showing an additional absorption band present in the oxygen-deficient samples compared to those grown via flux. This additional absorption is tunable via annealing post growth. Overall, this technique demonstrates the feasibility of growing large single crystals of Bi₂WO₆ with tunable W⁵⁺ centers for potential application in photocatalysis and quantum information.