Morphology Related Defectiveness in ZnO Luminescence: From Bulk to Nano-Size

Preparation and Application of Nanostructured ZnO in Radiation Detection

In order to adapt to the rapid development of high-speed imaging technology in recent years, it is very important to develop scintillators with an ultrafast time response. Because of its radiation-induced ultrafast decay time, ZnO has become an important material for radiation detection and dosimetry. According to different detection sources and application scenarios, ZnO is used in various radiation detectors in different structures, including nanoarrays and nanocomposites. In this paper, the synthesis methods and research status of various nanostructured ZnO-based materials and their applications in the detection of high-energy rays (X-rays, γ-rays) and high-energy particles (α, β and neutron) are reviewed. The performance discussion mainly includes spatial resolution, decay time and detection efficiency.

Tailoring SnO2 Defect States and Structure: Reviewing Bottom-Up Approaches to Control Size, Morphology, Electronic and Electrochemical Properties for Application in Batteries

Tin oxide (SnO₂) is a versatile n-type semiconductor with a wide bandgap of 3.6 eV that varies as a function of its polymorph, i.e., rutile, cubic or orthorhombic. In this review, we survey the crystal and electronic structures, bandgap and defect states of SnO₂. Subsequently, the significance of the defect states on the optical properties of SnO₂ is overviewed. Furthermore, we examine the influence of growth methods on the morphology and phase stabilization of SnO₂ for both thin-film deposition and nanoparticle synthesis. In general, thin-film growth techniques allow the stabilization of high-pressure SnO₂ phases via substrate-induced strain or doping. On the other hand, sol-gel synthesis allows precipitating rutile-SnO₂ nanostructures with high specific surfaces. These nanostructures display interesting electrochemical properties that are systematically examined in terms of their applicability to Li-ion battery anodes. Finally, the outlook provides the perspectives of SnO₂ as a candidate material for Li-ion batteries, while addressing its sustainability.

Photo- and radio-luminescence of porphyrin functionalized ZnO/SiO2 nanoparticles

The development of hybrid nanoscintillators is hunted for the implementation of modern detection technologies, like in high energy physics, homeland security, radioactive gas sensing, and medical imaging, as well as of the established therapies in radiation oncology, such as in X-ray activated photodynamic therapy. Engineering of the physico-chemical properties of nanoparticles (NPs) enables the manufacture of hybrids in which the conjugation of inorganic/organic components leads to increased multifunctionality and performance. However, the optimization of the properties of nanoparticles in combination with the use of ionizing radiation is not trivial: a complete knowledge on the structure, composition, physico-chemical features, and scintillation property relationships in hybrid nanomaterials is pivotal for any applications exploiting X-rays. In this paper, the design of hybrid nanoscintillators based on ZnO grown onto porous SiO₂ substrates (ZnO/SiO₂) has been performed in the view to create nanosystems potentially suitable in X-ray activated photodynamic therapy. Indeed, cytotoxic porphyrin dyes with increasing concentrations have been anchored on ZnO/SiO₂ nanoparticles through amino-silane moieties. Chemical and structural analyses correlated with photoluminescence reveal that radiative energy transfer between ZnO and porphyrins is the principal mechanism prompting the excitation of photosensitizers. The use of soft X-ray excitation results in a further sensitization of the porphyrin emission, due to augmented energy deposition promoted by ZnO in the surroundings of the chemically bound porphyrin. This finding unveils the cruciality of the design of hybrid nanoparticles in ruling the efficacy of the interaction between ionizing radiation and inorganic/organic moieties, and thus of the final nanomaterial performances towards the foreseen application.

Enhanced Luminance of CdSe/ZnS Quantum Dots Light-Emitting Diodes Using ZnO-Oleic Acid/ZnO Quantum Dots Double Electron Transport Layer

The widely used ZnO quantum dots (QDs) as an electron transport layer (ETL) in quantum dot light-emitting diodes (QLEDs) have one drawback. That the balancing of electrons and holes has not been effectively exploited due to the low hole blocking potential difference between the valence band (VB) (6.38 eV) of ZnO ETL and (6.3 eV) of CdSe/ZnS QDs. In this study, ZnO QDs chemically reacted with capping ligands of oleic acid (OA) to decrease the work function of 3.15 eV for ZnO QDs to 2.72~3.08 eV for the ZnO-OA QDs due to the charge transfer from ZnO to OA ligands and improve the efficiency for hole blocking as the VB was increased up to 7.22~7.23 eV. Compared to the QLEDs with a single ZnO QDs ETL, the ZnO-OA/ZnO QDs double ETLs optimize the energy level alignment between ZnO QDs and CdSe/ZnS QDs but also make the surface roughness of ZnO QDs smoother. The optimized glass/ITO/PEDOT:PSS/PVK//CdSe/ZnS//ZnO-OA/ZnO/Ag QLEDs enhances the maximum luminance by 5~9% and current efficiency by 16~35% over the QLEDs with a single ZnO QDs ETL, which can be explained in terms of trap-charge limited current (TCLC) and the Fowler-Nordheim (F-N) tunneling conduction mechanism.

Enhancement and tuning of the defect-induced electroluminescence of ZnO mesoporous layers in the visible range

We show a way to pattern the visible electroluminescence of solution-processed mesoporous ZnO layers. Our approach consists in locally changing the nanoscale morphology of the coated ZnO layers by patterning the underlying surface with thin metallic patches. Above the metal, the ZnO film is organized in clusters that enhance its defect-induced electroluminescence. The resulting emission occurs over a large continuum of wavelengths in the visible and near-infrared range. This broad emission continuum is filtered by thin film interferences that develop within the device, making it possible to fabricate LEDs with different colours by adjusting the thickness of their transparent electrode. When the metallic patterns used to change the morphology of the ZnO layer reach sub-micron dimensions, additional plasmonic effects arise, providing extra degrees of freedom to tune the colour and polarization of the emitted photons.

Tailoring the Thermal Conductivity of Rubber Nanocomposites by Inorganic Systems: Opportunities and Challenges for Their Application in Tires Formulation

The development of effective thermally conductive rubber nanocomposites for heat management represents a tricky point for several modern technologies, ranging from electronic devices to the tire industry. Since rubber materials generally exhibit poor thermal transfer, the addition of high loadings of different carbon-based or inorganic thermally conductive fillers is mandatory to achieve satisfactory heat dissipation performance. However, this dramatically alters the mechanical behavior of the final materials, representing a real limitation to their application. Moreover, upon fillers’ incorporation into the polymer matrix, interfacial thermal resistance arises due to differences between the phonon spectra and scattering at the hybrid interface between the phases. Thus, a suitable filler functionalization is required to avoid discontinuities in the thermal transfer. In this challenging scenario, the present review aims at summarizing the most recent efforts to improve the thermal conductivity of rubber nanocomposites by exploiting, in particular, inorganic and hybrid filler systems, focusing on those that may guarantee a viable transfer of lab-scale formulations to technological applicable solutions. The intrinsic relationship among the filler’s loading, structure, morphology, and interfacial features and the heat transfer in the rubber matrix will be explored in depth, with the ambition of providing some methodological tools for a more profitable design of thermally conductive rubber nanocomposites, especially those for the formulation of tires.