Amol Uttam Pawar

Tuning of the crystal engineering and photoelectrochemical properties of crystalline tungsten oxide for optoelectronic device applications

The photocatalysis, chromism, and sensing capabilities of nanostructured tungsten oxides, such as tungsten trioxide (WO3), its suboxides (WOx, 0 < x < 3) and hydrates (WO3·nH2O, n = 1/3 (0.33), 0.5, 0.75, 1, 2, etc.), tungsten bronzes MxWO3 (M = Li, Na, K, Rb, Cs and NH4), and metal tungstates (such as Bi2WO6 and CuWO4) have attracted much attention. To improve these properties, many strategies have been pursued, such as morphology control, doping, and heterostructuring. Crystal facet engineering has recently become a very important method of fine-tuning the physicochemical properties of semiconductors. The photocatalytic reactivity of a photocatalyst is significantly affected by its surface environment, including its surface electronic and atomic structures, which strongly depend on the crystal facets. It is believed that crystals with different exposed facets will have different properties, with the exposure of highly activated facets enhancing the photocatalytic and sensing properties. This article describes the syntheses of 2D WO3 crystals with the {002} facet primarily exposed, octahedral WO3 or WO3·nH2O with exposed {111} facets, and WO3 films with dominant orientations, such as orientation along the {002} facet. WO3 doping, WO3-based heterostructuring and their applications are also presented in this paper.

Red emitting Y2O3:Eu3+ nanophosphors with >80% down conversion efficiency

Obtaining nanophosphors of a controlled size and shape with a high quantum efficiency is the current challenge for display and imaging technologies. Although the surface state induced luminescence quenching in nanophosphors may be compensated to some extent by incorporating activators like rare-earth ions, or by exploiting their quantum size effect, obtaining nanophosphors with quantum efficiencies as high as their bulk counterparts remains elusive. In the present article, we report on the synthesis of uniform Eu-doped Y2O3 nanoparticles, with an average size of 20–53 nm and a down conversion efficiency as high as 85%, using a simple chemical precipitation technique. Along with size control, the effects of Eu3+ content on their emission behaviors have been discussed. We believe the low-cost synthesis process of these nanoparticles will greatly enhance their application potential in optical display and bio-imaging technologies.

Formation of a CdO Layer on CdS/ZnO Nanorod Arrays to Enhance their Photoelectrochemical Performance

The performance and photocatalytic activity of the well-known CdS/ZnO nanorod array system were improved significantly by the layer-by-layer heterojunction structure fabrication of a transparent conductive oxide (TCO) CdO layer on the CdS/ZnO nanorods. Accordingly, a CdO layer with a thickness of approximately 5-10 nm can be formed that surrounds the CdS/ZnO nanorod arrays after annealing at 500 °C under air. At an external potential of 0.0 V vs. Ag/AgCl, the CdO/CdS/ZnO nanorod array electrodes exhibit an increased incident photon to conversion efficiency, which is significantly higher than that of the CdS/ZnO nanorod array electrodes. The high charge separation between the electrons and holes at the interfaces of the heterojunction structure results from the specific band energy structure of the photoanode materials, and the unique high conductivity of the CdO layer is attributed to the suppression of electron-hole recombination; this suppression enhances the photocurrent density of the CdO/CdS/ZnO nanorod arrays. The photoresponse of the electrodes in an electrolytic solution without sacrificial agents indicated that the CdO layer also has the ability to suppress the well-known photocorrosive behavior of CdS/ZnO nanorods.

One-step transformation of Cu to Cu2O in alkaline solution

Cu can be directly transformed to Cu2O before forming CuO in high concentration NaOH aqueous solution by facile surface oxidation reaction without additional oxidant. By using different Cu substrates, pure Cu2O films with different dominant facets can be obtained.

Facile fabrication and photoelectrochemical properties of a one axis-oriented NiO thin film with a (111) dominant facet

A facile method was developed for the fabrication of a one axis-oriented p-type NiO monolayer film with a (111) dominant facet on ITO glass. Initially, hexagonal nanoplates of Ni(OH)2 were synthesized hydrothermally and these nanoplates were assembled as a one axis-oriented monolayered film on ITO glass. Mesoporous NiO with pore diameters of ca. 1.7 nm was obtained by heating the single crystalline Ni(OH)2 monolayered film at 400 °C for 3 h in air. The (111) facet oriented NiO thin film shows an enhanced photocathodic electrode activity with a photocurrent density of 0.38 mA cm−2 at a potential of −0.9 V vs. Ag/AgCl. For the first time, a mesoporous NiO thin film with an exposed (111) dominant facet has been fabricated and analyzed for use as a photoelectrode.

Fabrication of p-Cu2O/n-Bi-WO3 heterojunction thin films: optical and photoelectrochemical properties

A transparent n-type Bi-doped WO3 (Bi-WO3) thin film with a thickness of ca. 200 nm was fabricated on fluorine-doped tin oxide (FTO) coated glass using a facile spin-coating and annealing method. The compact WO3 layer with a very smooth surface highly enhanced the transmittance of the FTO substrate. Thin p-type Cu2O films with different morphologies were prepared on the Bi-WO3 film by electrodeposition of the same copper precursor solution with different pH values (7, 9 and 11). Magnetic stirring has a limited effect on the PEC performance of the films in our deposition system. The morphologies of the as-obtained films were characterized by scanning electron microscopy, which shows that the films were uniformly composed of nano-sized particles. The photoelectrochemical properties of the films were comparatively studied. Compared with the Bi-WO3 film, Cu2O/Bi-WO3 fabricated at pH 7 showed a better anodic photocurrent via the formation of a p–n heterojunction.