A single probe for solvent dependent optical recognition of iron(II/III) and arsenite: discrimination between iron redox states with single crystal X-ray structure evidence.

The detection and discrimination of Fe2+ and Fe3+ ions have been investigated using a simple probe (L), produced by the condensation of ethylenediamine and 3-ethoxysalicyaldehyde. Single crystal X-ray structures demonstrate that L interacts with Fe2+ and Fe3+. In aqueous-DMSO media, the L recognises AsO2- by fluorescence and colorimetry techniques. The AsO2- aided PET inhibition and H-bond assisted chelation enhanced fluorescence (CHEF) boost fluorescence by 91-fold. The L can detect 0.354 ppb Fe2+, 0.22 ppb Fe3+ and 0.235 ppt AsO2-.

Photoluminescence Quenching in CsPbCl3 upon Fe Doping: Colloidal Synthesis, Structural and Optical Properties.

Doped perovskite lead halide nanocrystals (PHNCs) are promising materials for various optoelectronic applications, but the major challenge faced by the researchers is the inability to dope foreign elements into perovskite lattice because of the strong lead-halide bond energies. In this work, we have used Fe as a dopant in CsPbCl3 to explore different doping techniques based on the colloidal synthesis of PHNCs to investigate the advantages and disadvantages of different techniques. We are able to dope a relatively higher amount of Fe (∼10%) than reported and observe clear optical signatures when the precursor does not have pre-existing Pb-Cl bonds. We prove that there are two competing processes inside a doped PHNC - one is the effect of dopant energy levels, and the other is surface passivation by halide ions. Using the most optimal synthesis strategy, we show that although Fe does act as a luminescence quencher in perovskite similar to II-VI quantum dots (QDs), the quenching requires much more Fe compared to trace amounts of Fe required in traditional QDs. Our work will assist in giving an overall comparative idea of doping and finding the most optimized strategy and help identify the underlying physical processes in perovskite based QDs.

Experimental Determination of the Molar Absorption Coefficient of Cesium Lead Halide Perovskite Quantum Dots.

Lead halide perovskite (CsPbX3, where X = Cl, Br, or I) quantum dots (QDs), with tunable optical and electronic properties, have attracted attention because of their promising applications in solar cells and next-generation optoelectronic devices. Hence, it is crucial to investigate in detail the fundamental size-dependent properties of these perovskite QDs to obtain high-quality nanocrystals for practical use. We propose a direct method for determining the concentration of solution-processed CsPbX3 QDs by means of spectrophotometry, in which the molar absorption coefficient (ε) is obtained using absorption and the Beer-Lambert law. By tuning the size of CsPbX3 QDs, we obtain their corresponding ε leading to a calibration curve for calculating the nanocrystal concentrations. The ε at the band edge for CsPbX3 (X = Cl, Br, or I) nanocrystals was found to be strongly dependent on the bandgap of the nanocrystals. We also obtained a reliable size dependence of the bandgap calibration curves to estimate the size of QDs from the absorption spectra.

Optimized study of the annealing effect on the electrical and structural properties of HDLC thin-films.

The plasma-enhanced chemical vapor deposition (PECVD) technique has been utilized for the facile surface deposition of hydrogenated diamond-like carbon (HDLC) thin-films onto Si(100) substrates. The as-deposited film surface is homogenous, free of pinholes, and adheres to the substrate. Annealing of the synthesized HDLC surface in a vacuum was performed in the temperature range of 200 to 1000 °C. A host of instrumental techniques, viz. FTIR spectroscopy, AFM, STM, and EC-AFM, were successfully employed to detect the morphological transformation in the HDLC films upon annealing. EC-AFM studies show irreversible biased behavior after undergoing a surface redox couple reaction and morphological change. Raman spectroscopy was carried out along with STM and EC-AFM to determine the functional nature and conductivity of the annealed surface.

Growth mechanistic insights into perovskite nanocrystals: dimensional growth.

The optical and electronic properties of lead halide perovskite nanocrystals have been explored extensively due to their increasing demand in photovoltaic and optoelectronic applications. But little is known about the growth kinetics of these nanocrystals. In this work, we demonstrate an interesting new mechanism using the method of arrested growth and precipitation to isolate the intermediates. We find that growth is driven by oriented attachment competing with the surface energetics. Hence, we observe a rare example of self-assembly driven dimensional growth characterized by suitable surface passivation that competes with the exposed surface facets through dimensional growth. This provides an explanation for not only the lack of size and shape tunability but also the emergence of a cubic shape rather than commonly observed spherical shapes in nanocrystals. Additionally, we find that this also corresponds to the observed phase transitions as well as correlating with pathways of decay of the photoluminescence spectra.

Hue- and Chromaticity-Based Exploration of Surface Complexation-Induced Tunable Emission from Non-Luminescent Quantum Dots.

Herein we report the use of a hue parameter of HSV (Hue, Saturation and Value) color space-in combination with chromaticity color coordinates-for exploring the complexation-induced luminescence color changes, ranging from blue to green to yellow to white, from a non-luminescent Fe-doped ZnS quantum dot (QD). Importantly, the surface complexation reaction helped a presynthesized non-luminescent Fe-doped ZnS QD to glow with different luminescence colors (such as blue, cyan, green, greenish-yellow, yellow) by virtue of the formation of various luminescent inorganic complexes (using different external organic ligands), while the simultaneous blue- and yellow-emitting complex formation on the surface of non-luminescent Fe-doped ZnS QD led to the generation of white light emission, with a hue mean value of 85 and a chromaticity of (0.28,0.33). Furthermore, the surface complexation-assisted incorporation of luminescence properties to a non-luminescent QD not only overcomes their restricted luminescence-based applications such as light-emitting, biological and sensing applications but also bring newer avenues towards unravelling the surface chemistry between QDs and inorganic complexes and the advantage of having an inorganic complex with QD for their aforementioned useful applications.

Excellent catalytic activity of magnetically recoverable Fe3O4-graphene oxide nanocomposites prepared by a simple method.

An Fe3O4-graphene oxide nanocomposite has been synthesized via a chemical reaction with a magnetite particle size of 18-25 nm. The resulting nanocomposite can be easily manipulated by an external magnetic field, exhibits excellent catalytic activity and may be reused for several cycles with marginal loss of activity. This recyclable nanocomposite provides an efficient, economic, novel route for multi-component A(3) coupling reactions of aldehydes, amines and alkynes and gives the propargylamine in excellent yields.