RESUMO
The structural and electronic properties of zinc clusters (Znn) for a size range of n = 2-15 are studied using density functional theory. The particle swarm optimization algorithm is employed to search the structure and to determine the ground-state structure of the neutral Zn clusters. The structural motifs are optimized using the density functional theory approach to ensure that the structures are fully relaxed. Results are compared with the literature to validate the accuracy of the prediction method. The binding energy per cluster is obtained and compared with the reported literature to study the stability of these structures. We further assess the electronic properties, including the ionization potential, using the all-electron FHI-aims code employing G0W0 calculations, and the G0W0Ð0(1) correction for a few smaller clusters, which provides a better estimation of the ionization potential compared to other methods.
RESUMO
The past decade has seen a rapid development in metal halide perovskite nanocrystals (NCs), which has been witnessed by their potential applications in nanotechnology. The inimitable chemical nature behind their unique photoluminescence characteristics has attracted a growing body of researchers. However, the low intrinsic stability and surface defects of perovskite NCs have hampered their widespread applications. Therefore, numerous techniques such as doping and encapsulation (polymer matrices, silica coating, salt matrix, etc.) have been examined for the surface modification of perovskite NCs and to increase their efficiency and stability. In this study, we demonstrated the self-passivation method for surface defects by introducing potassium (K) or rubidium (Rb) during the colloidal fabrication of NCs, resulting in the much-improved crystallinity, photoluminescence, and improved radiative efficiency. In addition, K-doped NCs showed a long-term colloidal stability of more than 1 month, which indicates the strong bonding between the NCs and the smaller-sized potassium cations (K+). We observed the enhancement of the radiative lifetime that can also be explained by the prevention of "Frenkel defects" when K+ stays at the interstitial site of the nanocrystal structure. Furthermore, our current findings signify the importance of surface modification techniques using alkali metal ions to reduce the surface traps of perovskite nanocrystals (PeNCs). Comparable developments could be applied to polycrystalline perovskite thin films to reduce the interface trap densities. The findings of this study have several important implications for future light-emitting applications.
RESUMO
Formamidinium lead bromide (FAPbBr3) nanocrystals have emerged as a powerful platform for optoelectronic applications due to their pure green photoluminescence (PL). However, their low colloidal stability under storage and operation reduces the potential use of FAPbBr3 perovskite nanocrystals (PeNCs) in various applications. In this study, we prepared the poly(L-lactic acid) (PLLA) nanofibrous membrane embedded with FAPbBr3 perovskite nanocrystals by electrospinning the perovskite and PLLA precursor solution. This is a simple and low-cost technique for the direct confinement of nano-sized functional materials in the continuous polymer nanofibres. PLLA as a polymer matrix provided a high surface framework to fully encapsulate the perovskite NCs. In addition, we found that FAPbBr3 PeNCs crystallize spontaneously inside the PLLA nanofibre. The resultant PLLA-FAPbBr3 nanofibrous membranes were stable and remained in the water for about 45 days without any evident decomposition. The results of this research support the idea of new possibilities for the production of air-stable FAPbBr3 PeNCs by forming a composite with PLLA polymer. The authors believe this study is a new milestone in the development of highly stable metal halide perovskite-based nanofibres, which allow for potential use in lasers, waveguides, and flexible energy harvesters.