Synthesis and Optical Properties of Mn2+-Doped Amino Lead Halide Molecular Clusters Assisted by Chloride Ion

Ultrafast Study of Excited State Dynamics of Amino Metal Halide Molecular Clusters

The excited state dynamics of ligand-passivated PbBr2 molecular clusters (MCs) in solution have been investigated for the first time using femtosecond transient absorption spectroscopy. The results uncover a transient bleach (TB) feature peaked around 404 nm, matching the ground state electronic absorption band peaked at 404 nm. The TB recovery signal can be fitted with a triple exponential with fast (10 ps), medium (350 ps), and long (1.8 ns) time constants. The medium and long time constants are very similar to those observed in the time-resolved photoluminescence (TRPL) decay monitored at 412 nm. The TB fast component is attributed to vibrational relaxation in the excited electronic state while the medium component with dominant amplitude is attributed to recombination between the relaxed electron and hole. The small amplitude slow component is assigned to electrons in a relatively long-lived excited electronic state, e.g., triplet state, or shallow trap state due to defects. This study provides new insights into the excited state dynamics of metal halide MCs.

Origin of the near 400 nm Absorption and Emission Band in the Synthesis of Cesium Lead Bromide Nanostructures: Metal Halide Molecular Clusters Rather Than Perovskite Magic-Sized Clusters

In the synthesis of cesium lead bromide (CsPbBr₃) perovskite quantum dots, with an electronic absorption and emission band around 510 nm, and perovskite magic-sized clusters (PMSCs), with an electronic absorption and emission band around 430 nm, another distinct absorption and emission around 400 nm is often observed. While many would attribute this band to small perovskite particles, here we show strong evidence that this band is a result of the formation of lead bromide molecular clusters (PbBr₂ MCs) passivated with ligands, which do not contain the A component of the ABX₃ perovskite structure. This evidence comes from a systematic comparative study of the reaction products with and without the A component under otherwise identical experimental conditions. The results support that the near 400 nm band originates from ligand-passivated PbBr₂ MCs. This observation seems to be quite general and is significant in understanding the nature of the reaction products in the synthesis of metal halide perovskite nanostructures.

Synthesis and Properties of Stable Amino Metal Halide Molecular Clusters in the Solid State

Nanosized molecular clusters (MCs) composed of PbBr₂ and neutral ligand butylamine (BTYA) with unique optical properties in solution and solid states have been synthesized using ligand-assisted reprecipitation and spin-coating, separately. The studies of their optical properties using ultraviolet-visible (UV-vis) absorption and photoluminescence (PL) show the first electronic absorption and PL band of the MCs at 401 and 411 nm, respectively, for the solution and solid state samples that exhibit good stability under ambient conditions. Low-temperature PL spectra below 30 K show vibronic peaks indicative of a single size or a very narrow size distribution of the MCs. On the basis of Raman, X-ray diffraction, and transmission electron microscopy measurements, a layered structural model is proposed for the MCs with a BTYA ligand capping on the surface of the corner-shared tilted [PbBr₆]^4- octahedral framework. The stable and retained structure of MCs in the solid state is promising for photonics applications.

Influence of Electrochemical Anticorrosion Technology on Concrete Structure and Performance

In order to solve the problem of steel bar desensitization in island concrete, which leads to steel bar corrosion and greatly reduces the service life of structures, this work studies the influence of electrochemical corrosion prevention technology on the structure and performance of concrete. Through linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS), the reinforcement in seawater sand concrete and ordinary concrete under two different chloride ion erosion modes was tested electrochemically, and then, its polarization curve and electrochemical impedance spectrum were obtained and analyzed. The experimental results show that the slope ratio of anode Tafel decreases significantly under the condition of steel bar passivation. The self-corrosion potential of reinforcement is −204 MV, which is much higher than −480 MV obtained from early testing. The self-corrosion potential obtained from the L3 polarization test tends to be stable after 84 days. As the test continues, the capacitive reactance arc in L1 and L2 medium-frequency region will gradually disappear with the continuous development of corrosion. Conclusion. This study explains the electrochemical mechanism and rate of reinforcement corrosion in seawater and sea sand concrete.

Impact of Molecular Ligands in the Synthesis and Transformation between Metal Halide Perovskite Quantum Dots and Magic Sized Clusters

Metal halide perovskite quantum dots (PQDs) and perovskite magic sized clusters (PMSCs) exhibit interesting size- and composition-dependent optoelectronic properties that are promising for emerging applications including photovoltaic solar cells and light-emitting diodes (LEDs). Much work has focused on developing new synthesis strategies to improve their structural stability and property tunability. In this paper, we review recent progress in the synthesis and characterization of PQDs and PMSCs, with a focus on the impact of different molecular ligands on their surface passivation and interconversion. Moreover, the effect of capping ligands on ion exchange during synthesis and doping is discussed. Finally, we present some perspectives on challenges and opportunities in fundamental studies and potential applications of both PQDs and PMSCs.