The study of optical band edge property of bismuth oxide nanowires α-Bi_2O_3

Abstract

The α-phase Bi(2)O(3) (α-Bi(2)O(3)) is a crucial and potential visiblelight photocatalyst material needless of intentional doping on accommodating band gap. The understanding on fundamental optical property of α-Bi(2)O(3) is important for its extended applications. In this study, bismuth oxide nanowires with diameters from tens to hundreds nm have been grown by vapor transport method driven with vapor-liquid-solid mechanism on Si substrate. High-resolution transmission electron microscopy and Raman measurement confirm α phase of monoclinic structure for the as-grown nanowires. The axial direction for the as-grown nanowires was along < 122 >. The band-edge structure of α-Bi(2)O(3) has been probed experimentally by thermoreflectance (TR) spectroscopy. The direct band gap was determined accurately to be 2.91 eV at 300 K. Temperaturedependent TR measurements of 30-300 K were carried out to evaluate temperature-energy shift and line-width broadening effect for the band edge of α-Bi(2)O(3) thin-film nanowires. Photoluminescence (PL) experiments at 30 and 300 K were carried out to identify band-edge emission as well as defect luminescence for the α-Bi(2)O(3) nanowires. On the basis of experimental analyses of TR and PL, optical characteristics of direct band edge of α-Bi(2)O(3) nanowires have thus been realized.

Sunlight induced formation of surface Bi2O4−–Bi2O3 nanocomposite during the photocatalytic mineralization of 2-chloro and 2-nitrophenol

“…6. The Raman peaks observed were in good agreement with the literature values [35]. The major Raman bands at 528.5, 448.5, 314.4, 211.3 and 152.4 cm −1 are attributed to skeletal Bi-O vibrations in as prepared Bi 2 O 3 .…”

Comparative study on photocatalytic performances of crystalline α- and β-Bi2O3 nanoparticles under visible light

“…2A seem that they are corresponding to A g mode. The results of the observed Raman shift frequencies and also the previous data reported by Denisov et al [43] and Ho et al [17] to the A g mode are represented in Table 2. Raman spectral studies confirmed that the prepared BiO-1 and BiO-2 samples are precisely single phase aBi 2 O 3 ; however, BiO-3 sample is b-phase of Bi 2 O 3 .…”

“…Stable phases are a-and d-Bi 2 O 3 , while the others are high-temperature metastable phases [29]. a-Bi 2 O 3 is thermodynamically the most stable phase in the range of 25 8C to 730 8C [17,30]. At 730 8C, aBi 2 O 3 transforms into d-phase and remains stable until reach its melting point at 825 8C [31].…”

“…However, it absorbs almost only the ultraviolet light (l < 400 nm), which means only 4-5% of visible solar spectrum can be utilized by TiO 2 owing to its high bandgap energy [15]. Among the active photocatalysts, Bi 2 O 3 has proven to be a valuable alternative photocatalyst to TiO 2 as it has suitable direct bandgap energy (less than 3.0 eV) [16,17]. Bi 2 O 3 is a p-type oxide semiconductor with many excellent physical and chemical properties.…”

“…At high cooling rates of d-phase, bphase can be observed near 650 8C then it can change back to a phase [32-35]. Among all polymorphs of Bi 2 O 3 , a-and b-phases has been employed effectively and sensitively in visible region [17]. Furthermore, there are some researchers reported recently that b-phase has higher photocatalytic performance than a-phase.…”