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The need to develop sustainable energy solutions is an urgent requirement for society, with the additional requirement to limit dependence on critical raw materials, within a virtuous circular economy model. In this framework, it is essential to identify new avenues for light‐conversion into clean energy and fuels exploiting largely available materials and green production methods. Metal oxide semiconductors (MOSs) emerge among other species for their remarkable environmental stability, chemical tunability, and optoelectronic properties. MOSs are often key constituents in next generation energy devices, mainly in the role of charge selective layers. Their use as light harvesters is hitherto rather limited, but progressively emerging. One of the key strategies to boost their properties involves doping, that can improve charge mobility, light absorption and tune band structures to maximize charge separation at heterojunctions. In this review, effective methods to dope MOSs and to exploit the derived benefits in relation to performance enhancement in different types of devices are identified and critically compared. The work is focused specifically on the best opportunities coming from the use of non‐critical raw materials, so as to contribute in defining an economically feasible roadmap for light conversion technologies based on these highly stable and widely available compounds. [ABSTRACT FROM AUTHOR]

The wide interest in developing green energy technologies stimulates the scientific community to seek, for devices, new substitute material platforms with a low environmental impact, ease of production and processing and long-term stability. The synthesis of metal oxide (MO) semiconductors fulfils these requirements and efforts are addressed towards optimizing their functional properties through the improvement of charge mobility or energy level alignment. Two MOs have rising perspectives for application in light harvesting devices, mainly for the role of charge selective layers but also as light absorbers, namely MoO3 (an electron blocking layer) and Co3O4 (a small band gap semiconductor). The need to achieve better charge transport has prompted us to explore strategies for the doping of MoO3 and Co3O4 with vanadium (V) ions that, when combined with oxygen in V2O5, produce a high work function MO. We report on subcritical hydrothermal synthesis of V-doped mesostructures of MoO3 and of Co3O4, in which a tight control of the doping is exerted by tuning the relative amounts of reactants. We accomplished a full analytical characterization of these V-doped MOs that unambiguously demonstrates the incorporation of the vanadium ions in the host material, as well as the effects on the optical properties and work function. We foresee a promising future use of these materials as charge selective materials in energy devices based on multilayer structures. [ABSTRACT FROM AUTHOR]

The aim of this work was i) to develop a hydrothermal, low‐temperature synthesis protocol affording the upconverting hexagonal phase NaYF4 with suitable dopants while adhering to the "green chemistry" standards and ii) to explore the effect that different parameters have on the products. In optimizing the synthesis protocol, short reaction times and low temperatures (below 150 °C) were considered. Yb3+ and Er3+ ions were chosen as dopants for the NaYF4 material. Within the context of the second goal, parameters including nature of the precursors, treatment temperature, and treatment time were investigated to afford a pure hexagonal crystalline phase, both in the doped and undoped materials. To fully explore the synthesis results, the prepared materials were characterized from a structural (XRD), compositional (XPS, ICP‐MS), and morphological (SEM) point of view. The upconverting properties of the compounds were confirmed by photoluminescence measurements. [ABSTRACT FROM AUTHOR]

An inverse (water in oil) miniemulsion technique was successfully implemented for the first time for the synthesis of crystalline pure and doped CuS nanostructures for applications in photothermal therapy. Different copper and sulfur sources were tested for the preparation of the targeted compounds. The successful formation at room temperature of the covellite crystalline phase was determined by means of X-ray diffraction crystallography, selected-area electron diffraction, and X-ray absorption spectroscopy. The morphology of the nanostructures was assessed by scanning and transmission electron microscopy, while the surface composition was determined by X-ray photoelectron spectroscopy. Further investigations, aimed at obtaining a characterization as detailed as possible, were performed by combining the outcomes of complementary techniques. Droplet-size variations, as a function of sonication time and/or mode, were studied using dynamic light-scattering measurements. A high microscopic photothermal conversion efficiency – a relevant property for photothermal therapy and photoacoustic imaging – was determined by calibrated optoacoustic measurements. The photothermal efficiency of diluted aqueous dispersions of the CuS nanostructures is ≥ 0.72, as determined by laser excitation at 1064 nm. [ABSTRACT FROM AUTHOR]

The controlled, room-temperature synthesis of M-doped (M = CuII, MnII, SmIII, GdIII, or TbII) ZnS nanostructures (with an average crystallite size of 5-10 nm) in the confined space of miniemulsion droplets is reported herein and discussed. The adopted synthetic route is a colloidal method, ideally suited to easily achieve small particle size and narrow size distribution. The synthesized functional nanostructures crystallize in the sphalerite lattice, as determined by powder X-ray diffraction. In addition to structural characterization, several complementary techniques, such as X-ray photoelectron spectroscopy, thermogravimetric analysis, differential scanning calorimetry, micro-Raman spectroscopy, inductively coupled plasma mass spectrometry, and Fourier transform infrared spectroscopy were used to determine chemical and physical properties as well as the microstructural features of our products. As far as the morphological aspects of the obtained samples are concerned, they were studied by means of scanning and transmission electron microscopies. Finally, the local structure around dopant ions was unravelled by means of X-ray absorption spectroscopy, in particular through extended X-ray absorption fine structure measurements carried out at the Zn, S, and dopant K or L3 edges. This information has been complemented with the investigation of the photoluminescence properties. [ABSTRACT FROM AUTHOR]

Doped M:ZnO nanoparticles (Zn/M = 50:1 or 20:1; M = AgI, CoII, CuII, EuIII, MgII, MnII) have been produced by an easy, reproducible, and fast inverse miniemulsion approach, enabling the co-precipitation of the nanocrystalline oxide in a confined space. Unexpectedly, the formation of crystalline materials took place at room temperature. Suspensions were characterized by dynamic light scattering and UV/Vis spectroscopy, whereas precipitated powders were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy, inductively coupled plasma atomic emission spectrometry, and thermogravimetric analysis. The particles obtained showed preferential growth along the [0002] direction with a size of 70 nm, whereas along the other directions average sizes of between 26 and 33 nm were determined. The analyses confirmed successful doping in all cases but one: In fact, the Ag-doped sample is a nanocomposite consisting of metallic silver clusters dispersed in the ZnO matrix. Red emission from the ZnO:Eu sample was evidenced upon excitation at around 465 nm. [ABSTRACT FROM AUTHOR]