Blue or red photoluminescence emission in α-Bi2 O3 needles: Effect of synthesis method.

Monoclinic bismuth oxide (α-Bi2 O3 ) has attractive optical properties and, therefore, its photoluminescence (PL) behavior has been increasingly explored. Besides this fact, the influence of synthesis methods on PL properties of α-Bi2 O3 still requires research. This paper describes the influence of precipitation (PPT) and microwave-assisted hydrothermal (MAH) methods on PL properties of acicular α-Bi2 O3 microcrystals. The synthesis method promoted structural modifications on α-Bi2 O3 , in particular PPT increased the density of oxygen vacancies significantly. As a result, the PL properties of samples were different depending on the method of synthesis. PPT samples presented their maximum PL emission at 1.91 eV (red), while MAH samples had their maximum at 2.61 eV (blue). These results indicate the possibility of controlling PL properties of α-Bi2 O3 by simply choosing the adequate synthesis method.

Effect of Pressure-Assisted Heat Treatment on Photoluminescence Emission of α-Bi2O3 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-Bi2O3) 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-Bi2O3 with a needlelike morphology, which was synthesized via a microwave-assisted hydrothermal (MAH) method. PAHT caused an angular increase between the [BiO6]-[BiO6] clusters of α-Bi2O3, resulting in a significant increase in the PL emission intensity. The Raman and XPS spectra also showed that the α-Bi2O3 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).