Effect of Pressure-Assisted Heat Treatment on Photoluminescence Emission of α‑Bi<sub>2</sub>O<sub>3</sub> Needles

Materials with high photoluminescence (PL) intensity can potentially be used in optical and electronic devices. Although the PL properties of bismuth­(III) oxide with a monoclinic crystal structure (α-Bi<sub>2</sub>O<sub>3</sub>) have been explored in the past few years, methods of increasing PL emission intensity and information relating PL emission to structural defects are scarce. This research evaluated the effect of a pressure-assisted heat treatment (PAHT) on the PL properties of α-Bi<sub>2</sub>O<sub>3</sub> with a needlelike morphology, which was synthesized via a microwave-assisted hydrothermal (MAH) method. PAHT caused an angular increase between the [BiO<sub>6</sub>]–[BiO<sub>6</sub>] clusters of α-Bi<sub>2</sub>O<sub>3</sub>, resulting in a significant increase in the PL emission intensity. The Raman and XPS spectra also showed that the α-Bi<sub>2</sub>O<sub>3</sub> PL emissions in the low-energy region (below ∼2.1 eV) are attributed to oxygen vacancies that form defect donor states. The experimental results are in good agreement with first-principles total-energy calculations that were carried out within periodic density functional theory (DFT).