Brazilian Journal of Physics最新文献

This work aims to contribute to the understanding of the archaeological contexts of the Xingó subregion, located on the lower São Francisco River. Ceramic fragments from six archaeological sites in the region were studied using archaeometric techniques. The proposal is to extend the archaeometric analysis of small sites located upstream, which have been the subject of little research. The Justino site was used as a reference because the one is the best studied in the region to date. To this end, the regional context, already covered, is investigated further, and the activities carried out at the sites studied are described. X-ray diffractometry (XRD), X-ray fluorescence (XRF), Fourier-transform infrared (FTIR), and scanning electron microscopy (SEM) were some of the techniques used in this study. FTIR and thermal analysis suggest that pottery was fired above 500 °C. FTIR/SEM analysis indicated the macroscopic presence of minerals in the clays from different sites. This study also expands on the possibility that added temper containing organic matter in the Justino ceramics may indicate the presence of caraipé (tree bark) in the Xingó region. The presence of this typical Amazonian and Brazilian Cerrado (savannah) temper in Lower São Francisco would provide a framework for understanding precolonial connections between the regions.

Carbon dots are one of the emerging nanomaterials within the family of carbon-based nanostructures. The spherical structure and fascinating properties of carbon dots have been recognized for their potential applications in various research fields, such as food packaging, biological sensing, optical technology, drug delivery, photodynamic therapy, photocatalysis, and solar cells. Especially, carbon dots have been captivated as potential candidates for food packaging applications due to their antibacterial, biocompatibility, and antioxidant properties as well as their nontoxic nature and low processing cost. Traditionally, two technical routes have been employed for the preparation of carbon dots: the bottom-up method and the top-down method. Each method has its own advantages over other methods, and these methods exhibit a unique characteristic property for its applications. This review provides clear and in-depth insights into the various preparation methods and their influence on the physical properties and characteristics of carbon dots. The preparation methods for carbon dot such as bottom-up and top-down approaches were also summarized in detail, and the effects of preparation methods of both approaches and their influence on the physical, chemical, and morphological property of carbon dots are discussed comprehensively. In addition, comprehensive information is provided about the various synthesis parameters and precursors used in the preparation plans of carbon dots and characterization influenced by methods that could be helpful to the researcher in choosing the carbon dot methodology for food packaging application.

Graphical Abstract

We looked at Xe-induced fusion reactions that resulted in the formation of the SHE Z=119. In this view, we considered four projectiles such as (^{130})Xe, (^{132})Xe, (^{134})Xe, and (^{136})Xe on (^{157-159})Tb. For the study of evaporation residue cross-sections, we investigated 12 fusion processes in total. Using an advanced statistical model, we assessed the probability of compound nucleus formation ((P_{CN})), survival probability((P_{Sur})), and evaporation residue cross-sections ((sigma _{EVR})). The measured ((P_{CN})) at optimal energy decreases as the mass number of projectile nuclei increases. In contrast, as the projectile-mass number increases, so does the likelihood of survival. For (^{136})Xe+(^{159})Tb fusion reaction, the (P_{Sur}) and (sigma _{EVR}) are found higher value. When Xe-induced fusion events were considered, the expected cross-sections, which are in the order larger than femtobarn range, will serve as a roadmap for the synthesis of the SHE Z=119.

Diffusivity, conductivity, and viscosity data of the PbO⋅SiO₂ were collected in the liquid, supercooled liquid, and glassy states. The difference in the dependence of diffusivity, viscous flow, and ionic conductivity on temperature below and above the glass transition temperature (T_g) is interpreted as a discontinuity in the charge carrier’s mobility mechanisms, including new proposals for ionic diffusivity. Charge carrier displacement occurs by an activated mechanism below T_g and through a cooperative mechanism above this temperature. Fitting diffusivity and conductivity data with the proposed model allows one to determine the enthalpies of charge carrier formation and migration separately. In particular, we present experimental results of lead and silicon diffusion species (D_Pb and D_Si) at deep and low undercoolings in PbSiO₃—considering 16 orders of magnitude and comparing the effective diffusivity for viscous flow, D_η, and its activation energy. A decoupling temperature T_d between the cationic diffusivity and the diffusivity calculated from viscosity, i.e., D_η < (D_Si ≈ D_Pb) was noted. In fact, a noticeable change in the lead self-diffusion coefficients around T_d = 1.19T_g also contributed to this analysis. Thus, above T_d, silicon and lead control the transport mechanism involved in viscous flow, while below this temperature some simpler structures must control the transport process. Such results suggest that viscous flow requires a cooperative motion of some “structural units” rather than just jumps of one or a few isolated atoms, as it occurs in conductivity below T_d. Also, cooperatively rearranging regions or the size of the structural units are quite similar for both processes above T_d.

Our heavy reliance on fossil fuels has taken a massive toll on us. The quickly depleting reserve of fossil fuels and its impact on the environment have prompted mankind to look for sustainable and eco-friendly alternatives. Among many renewable energy sources being implicated and investigated in this regard, solar energy has found a special importance, and its implication offers acknowledgement to unlimited energy provided by the sun cantered in our solar system. Perovskite solar cells (PSCs) are one of the most popularly researched solar cells that have already shown incredible ability to harness solar energy. At the onset, organic-inorganic hybrid PSCs showed great potential but their degradation upon exposure to moisture, heat, oxygen, and even light has cornered them. Recently, CsPbI₃-based PSCs have shown great promise in terms of power conversion efficiency (PCE). However, they do suffer from some sort of instability at ambient conditions. To counteract this dilemma, many strategies are being implemented by scientists around the globe. This review highlights some recent advances in the field of CsPbI₃-based PSCs specifically. In addition to that, some approaches have been suggested that how both the PCE and stability can be improved further.

Graphical Abstract

This paper reports the spectral and kinetic features of the up- and downconversion photoluminescence (PL) of (1%, 2%, 3%, 4%, and 5%) Nd-doped BaSrSiO₄ silicates to elucidate the fundamental processes of UCPL. This manuscript discusses the energy transition levels and potential excitation processes. The sol-gel method was utilized for synthesizing Nd-doped BaSrSiO₄ nanocrystals, which were then annealed at 600 °C to produce silicates. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to determine the crystal phase and nanocrystal formation of the synthesized Nd-doped BaSrSiO₄ powders. When activated by various UV–visible wavelengths, the PL downconversion (DCPL) from a sample exhibits well-resolved bands with sub-split lines centered at 890 nm associated with the near-infrared transitions in Nd³⁺ ions. Quenching occurred at 5% doping due to multipolar interactions, indicating that 4% doping is appropriate for temperature sensing applications. Conversely, a visible upconversion PL (UCPL) has been found when excited by a pulsed laser of 800 nm. Furthermore, the suggested energy levels for the upconversion process were verified using the UCPL and photoluminescence excitation (PLE) data. Our results imply that the excited-state absorption mechanism (ESA) in rare earth (Nd)-doped BaSrSiO₄ is most likely a potential mechanism of the UCPL process. The TL glow peak shows the highest intensity for 4 mol% Nd³⁺-doped BaSrSiO₄ at 88 °C. Quenching at 5% was observed due to the dissipation of the trapping centers.