Editorial: Colloidal Semiconductor Nanocrystals: Synthesis, Properties, and Applications

Solution-Processed Inorganic Thermoelectric Materials: Opportunities and Challenges

Thermoelectric technology requires synthesizing complex materials where not only the crystal structure but also other structural features such as defects, grain size and orientation, and interfaces must be controlled. To date, conventional solid-state techniques are unable to provide this level of control. Herein, we present a synthetic approach in which dense inorganic thermoelectric materials are produced by the consolidation of well-defined nanoparticle powders. The idea is that controlling the characteristics of the powder allows the chemical transformations that take place during consolidation to be guided, ultimately yielding inorganic solids with targeted features. Different from conventional methods, syntheses in solution can produce particles with unprecedented control over their size, shape, crystal structure, composition, and surface chemistry. However, to date, most works have focused only on the low-cost benefits of this strategy. In this perspective, we first cover the opportunities that solution processing of the powder offers, emphasizing the potential structural features that can be controlled by precisely engineering the inorganic core of the particle, the surface, and the organization of the particles before consolidation. We then discuss the challenges of this synthetic approach and more practical matters related to solution processing. Finally, we suggest some good practices for adequate knowledge transfer and improving reproducibility among different laboratories.

Optical Characterization of Bitumen: Inspecting the Quantum Size Effect in the Nanostructured Phase

Bitumen (BIT) is an oil sub-product with many applications. A variety of literature reports the analysis of its optical properties, as the fluorescence and the Fourier transform infrared (FT-IR) optical transmittance (OT). We have performed photoluminescence (PL) on the visible region of the spectrum and OT on the visible-NIR in solutions of BIT in toluene at different concentrations. The results revealed a nonlinear, concentration-dependent effect attributed to intermolecular solvent-solute interactions. PL analysis of pure BIT as a function of the temperature and the laser pumping power pointed to the existence of nanosized crystalline inclusions on the amorphous BIT matrix with noticeable optical properties. The inference was confronted with the results of X-ray diffraction studies and literature reports. The possibility of the occurrence of a quantum size effect governing the luminescence is considered.

High-yield synthesis of CsPbBr3nanoparticles: diphenylphosphine as a reducing agent and its effect in Pb-seeding nucleation and growth

Based on the reported nucleation mechanisms for CsPbX₃and II-VI/IV-VI quantum dots, CsPbBr₃nanoparticles with a higher reaction-yield (up to 393% mass-increment) were synthetized by the hot-injection method. The introduction of diphenylphosphine (DPP) as a reducing agent improved nanoparticle nucleation and growth, giving out evidence for Pb-seeding in CsPbBr₃nanoparticles formation. Additionally, a clear influence of the DPP in a CsPbBr₃-Cs₄PbBr₆incomplete phase transformation was observed, marked by the appearance of several PbBr₂nanoparticles. This indicated the need for an improved ratio between the stabilizing agents and the precursors, due to the increased number of nucleation sites produced by DPP. The resulting CsPbBr₃nanoparticles showed high quality, as they displayed 70%-90% photoluminescence quantum yield; narrow size distribution with an average nanoparticle size of∼10 nm; and the characteristic cubic morphology reported in previous works. This increment in CsPbBr₃nanoparticles' reaction yield will contribute to making them a more attractive option for different optoelectronic applications.