Tunable W⁵⁺ Absorbance in Laser Floating Zone Grown Bismuth Tungstate

Abstract

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 Bi2WO6–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.