Toward an Understanding of Intermediate- and Short-Range Defects in ZnO Single Crystals. A Combined Experimental and Theoretical Study

ZnO twin-rods decorated with Pt nanoparticles for butanone detection

ZnO twin-rods were synthesized using a combination of the ultrasonic spray nozzle and microwave-assisted hydrothermal methods. The VOC detection test revealed that the decoration with 2% of Pt provides a more sensitive and selective butanone sensor.

One step microwave-hydrothermal synthesis of rGO–TiO2 nanocomposites for enhanced electrochemical oxygen evolution reaction

rGO–TiO₂ nanocomposites exhibited greater electrocatalytic activity for H₂O oxidation in neutral and alkaline medium as compared with pure TiO₂.

Joint Theoretical and Experimental Study on the La Doping Process in In2O3: Phase Transition and Electrocatalytic Activity

In₂O₃ and La³⁺-doped In₂O₃ nanostructures were synthesized through a facile and fast chemical route based on the microwave-assisted hydrothermal method combined with rapid thermal treatment in a microwave oven. The presence of the La³⁺ doping process modifies the size and morphology of the In₂O₃ nanostructures and also stabilizes the rhombohedral (rh) In₂O₃ phase with respect to the most stable cubic (bcc) polymorph. X-ray diffraction (XRD) patterns and Rietveld refinements, Raman, UV-vis, and energy dispersive X-ray (EDX) spectroscopies, transmission electron (TEM) and field-emission scanning electron (FE-SEM) microscopies, as well as PL emissions have been performed. To complement and rationalize the experimental results, first-principle calculations, based on density functional theory, are carried out to obtain the formation energies of the In₂O₃ and bcc- and rh-In₂O₃-doped phases, their geometry and electronic properties. Theoretical results are able to explain the relative stabilization of the rh-phase with respect to the bcc-phase based on the analysis geometry changes and the electronic redistribution induced by the La³⁺ doping process. In addition, Wulff construction is employed to match the theoretical and experimental morphologies of the cubic phase. The synthesized samples were applied for the O₂ evolution reaction (OER). The La³⁺-doped In₂O₃ film presents superior electrocatalytic activity, with an onset potential lower than the undoped In₂O₃ film that can be associated with the increase in electron density caused by the La³⁺ doping process. This study provides a versatile strategy for obtaining In₂O₃ and La³⁺-doped In₂O₃ nanostructures for practical applications.

An extreme high-performance ultraviolet photovoltaic detector based on a ZnO nanorods/phenanthrene heterojunction

ZnO nanorods/Phen heterojunction based UV photovoltaic detector is fabricated which shows an extremely high performance with a detectivity up to ∼9.0 × 10¹³ Jones.

Synthesis of hierarchical WO3 nanostructured thin films with enhanced electrochromic performance for switchable smart windows

Graphical representation of synthesis of hierarchical WO₃ nanostructured thin films via electrodeposition method.

ZnO-NANOCRYSTALS IN STRONG CONFINEMENT REGIMES: INSIGHT ON RELAXATION DYNAMICS OF DEFECT STATES RESPONSIBLE FOR THE VISIBLE LUMINESCENCE

The broad visible photoluminescence (PL) observed in ZnO nanocrystals (NCs) is widely attributed to multiple low lying surface-defects. We have performed steady state and time-resolved PL measurements on size-selected ZnO NCs in the strong confinement regimes. Our results show that radiative relaxation rates and coupling between excitons and surface defect states vary dramatically for sizes between 2 nm and 3 nm. Energy dependent PL lifetimes reveal that relaxation dynamics of these defect states in the blue- and red-edge of the emission are very different from each other.

Spectrally Resolved Photoluminescence Imaging of ZnO Nanocrystals at Single-Particle Levels

The intrinsic spectral line widths of defect-related transitions in quantum-confined semiconductor nanocrystals are often difficult to estimate using ensemble measurements because the extent of inhomogeneous broadening due to particle size distributions is not known precisely. To address this problem, we performed spectrally resolved photoluminescence (PL) microscopy of individual ZnO NC by directly populating the defects states using low-energy laser excitation. The temporal evolution of PL intensities shows discrete blinking behaviors, suggesting that the NCs are detected near single-particle levels. The transition energies of individual NCs are found to fluctuate around their mean position (2.25 eV) by ∼0.130 eV, which is attributed to particle size distribution and defects densities associated with each NC. The spectral line width associated with defect emission envelope of ZnO NCs is found to be inherently broad (200-400 meV), which further establishes the presence of multiple closely spaced defect energy levels within every ZnO NC.