Rational Design of the Alkali Metal Sn-Based Mixed Halides with Large Birefringence and Wide Transparent Range.

Birefringent materials are widely used in various advanced optical systems, owing to their vital role in creating and controlling polarized light. Currently, Sn2+-based compounds containing stereochemically active lone-pair (SCALP) cations are extensively investigated and considered as one class of promising birefringent materials. To solve the problem of relatively narrow bandgap of Sn2+-based compounds, alkali metals and multiple halogens are introduced to widen the bandgap during the research. Based on this strategy, four new Sn2+-based halides, A2Sn2F5Cl and ASnFCl2 (A = Rb and Cs), with large birefringence, short ultraviolet (UV) cutoff edge, and wide transparent range are successfully found. The birefringences of A2Sn2F5Cl (A = Rb and Cs) are 0.31 and 0.28 at 532 nm, respectively, which are among the largest in Sn-based halide family. Remarkably, A2Sn2F5Cl possess relatively shorter UV cutoff edge (<300 nm) and broad infrared (IR) transparent range (up to 16.6 µm), so they can become promising candidates as birefringent materials applied in both UV and IR regions. In addition, a comprehensive analysis on crystal structures and structure-property relationship of metal Sn2+-based halides is performed to fully understand this family. Therefore, this work provides insights into designing birefringent materials with balanced optical properties.

Mechanism Understanding for Size Regulation of Silver Nanowires Mediated by Halogen Ions.

The controllable preparation of silver nanowires (AgNWs) with a high aspect ratio is key for enabling their applications on a large scale. Herein, the aspect ratio regulation of AgNWs mediated by halogen ion composition in ethylene glycol system was systematically investigated and the size evolution mechanism is elaborately understood. The co-addition of Br- and Cl- results in AgNWs with the highest aspect ratio of 1031. The surface physicochemical analysis of AgNWs and the density functional theory calculations indicate that the co-addition of Br- and Cl- contributes to the much-enhanced preferential growth of the Ag(111) crystal plane. At the same time, when Cl- and Br- coexist in the solution, the growth of the Ag(100) crystal plane on the AgNWs was restrained compared with that in the single Cl- system. Resultantly, the enhanced growth of Ag(111) and the inhibited growth of Ag(100) contribute to the formation of AgNWs with a higher aspect ratio in the Cl-Br mixed solution. The results can provide new insights for understanding the morphology and size evolution during the AgNWs preparation in ethylene glycol system.

Halogen ion-modified silver nanoparticles for ultrasensitive surface-enhanced Raman spectroscopy detection of polycyclic aromatic hydrocarbons.

Rapid ultrasensitive detection of trace polycyclic aromatic hydrocarbons (PAHs) is essential and significant for pollution control due to their hazard, persistence, and the wide distribution in the environment. Therefore, rapid detection of PAHs is critical for controlling pollution and protecting the ecology. Considering the advantages of surface-enhanced Raman spectroscopy (SERS), a simple and reliable SERS method was proposed in this work for detecting PAHs in water. Three chemicals, namely NaCl, KBr, and KI, were chosen to modify Ag nanoparticles (NPs) for phenanthrene (Phe) detection, and Ag NPs modified with KBr (Ag-Br NPs) showed the best SERS response. The mixing sequence and the concentration of KBr were optimized. The addition order of mixing KBr and Ag NPs before Phe solution was the best sequence, and the optimal concentration of KBr was 20 mM. Under optimal conditions, the limits of quantification for Phe, pyrene (Pyr), and anthracene (Ant) were 10-6  M, 10-7  M, and 10-7  M, respectively. Mixed PAHs (Phe, Pyr, and Ant) in spiked water samples were identified and quantified successfully. The proposed method has good application prospects in environmental pollution monitoring.

Combined effects of high relative humidity and ultraviolet irradiation: Enhancing the production of gaseous NO2 from the photolysis of NH4NO3.

Free radicals and nitrogen-containing species produced by nitrate photolysis can affect various atmospheric chemical processes, and thereby the photochemical behavior of atmospheric nitrate aerosols has been attracting much attention. However, the photolysis mechanism of NH4NO3 and its products under different atmospheric conditions remain unclear. In this study, the effects of relative humidity (RH), pH, NH3, ultraviolet (UV) light intensity and halogen ions (Cl-, Br- and I-) on the photolysis of particulate NH4NO3 have been investigated through a flow tube reactor. The results show that RH can significantly enhance the production of gaseous NO2 from the photolysis of NH4NO3 when RH is higher than its deliquescence RH, but almost no NO2 is generated under dry conditions. Under high RH and UV light, the main product of NH4NO3 photolysis is NO2, rather than NO and HONO, and another main species HNO3 which mainly comes from the hydrolysis of product NO2 in the gas path was detected. Almost no NO2 and HNO3 are produced under high RH without UV light or low RH with UV light, showing the combined effect of high RH and UV irradiation on the photolysis of NH4NO3. In addition, under high RH, the lower the pH and the stronger the light intensity, the higher the NO2 production. Furthermore, surprising yields of NO and HONO are detected in the presence of halogen ions, especially in the presence of I-, indicating the important role of halogen ion in the nitrate photolysis. These results provide new insights into the photolysis of atmospheric nitrate aerosols, and may contribute to elucidating the formation and migration of atmospheric nitrate aerosols and the potential mechanisms of the occurrence and evolution of atmospheric pollution and ozone pollution.

Synergistic Effect of Halogen Ions and Shelling Temperature on Anion Exchange Induced Interfacial Restructuring for Highly Efficient Blue Emissive InP/ZnS Quantum Dots.

InP quantum dots (QDs) have attracted much attention owing to their nontoxic properties and shown great potential in optoelectronic applications. Due to the surface defects and lattice mismatch, the interfacial structure of InP/ZnS QDs plays a significant role in their performance. Herein, the formation of In-S and Sx -In-P1-x interlayers through anion exchange at the shell-growth stage is revealed. More importantly, it is proposed that the composition of interface is dependent on the synergistic effect of halogen ions and shelling temperature. High shelling temperature contributes to the optical performance improvement resulting from the formation of interlayers, besides the thicker ZnS shell. Moreover, the effect relates to the halogen ions where I- presents more obvious enhancement than Br- and Cl- , owing to their different ability to coordinate with In dangling bonds, which are inclined to form In-S and Sx -In-P1-x bonds. Further, the anion exchange under I- -rich environment causes a blue-shift of emission wavelength with shelling temperature increasing, unobserved in a Cl- - or Br- -rich environment. It contributes to the preparation of highly efficient blue emissive InP/ZnS QDs with emission wavelength of 473 nm, photoluminescence quantum yield of ≈50% and full width at half maximum of 47 nm.

A Correction Method for Attenuated Total Reflection-Far Ultraviolet Spectra Via the Use of Charge Transfer to Solvent Band Intensities of Iodide in the Ultraviolet Region.

Attenuated total reflection (ATR) spectra, which are often used in IR analysis, can be transformed into extinction and refraction spectra by Kramers-Kronig transformation (KKT) with Fresnel equations. However, it is often difficult to obtain correct optical indices due to the inherent instrumental functions. This paper proposes a simple practical method for correction of KKT with two parameters, which include all the effects of the instrumental function. In order to obtain the parameters of the instrumental function, absorption ratios of charge transfer to solvent (CTTS) transitions of aqueous iodide ions observed at 195 nm and 230 nm were used as a standard. The absorption indices calculated from the ATR spectra with the parameters correspond reasonably well to those given by the transmittance spectra not only in the UV region but also in the far-ultraviolet (FUV, 120-200 nm) region. By applying the corrected KKT to the ATR-FUV spectra of aqueous potassium halide solutions in the range of 0-2 M, correct features of the absorption spectra of KCl and KBr, whose CTTS bands are thought to be observed in FUV region, were confirmed. It is possible to use the parameters representing the instrument function as long as the instrument is not changed.