A comprehensive understanding of exciton dynamics of water-soluble quantum dots (QDs), especially those synthesized directly in aqueous media, is critical for devising their applications. Trapping processes are expected to play a pivotal role here, as surface trap states are abundant in such QDs. The present study, based on ultrafast transient absorption, provides insight into exciton dynamics in PEI-capped CdS QDs synthesized by a one-pot reaction in water. They are robust and strongly photoluminescent (PL), unlike many other aqueous QDs. Excitation energy dependence of PL and the underlying mechanisms have been investigated. Analysis of fluence-dependent transient absorption bleach and photoinduced absorption is performed to deconvolute contributions from multiexciton recombination and carrier trapping. A simple kinetic model is used to quantify the rate constants associated with intraband relaxation of hot excitons and hot carrier trapping. Similar magnitudes observed for the two pathways highlight the competitive kinetics between them, which is responsible for a drastic decrease in PL quantum yields for excitation above the band gap. Such efficient hot carrier trapping in these QDs may possibly foreshadow ultrafast trap-mediated electron transfer and thus render them suitable for redox-sensing and photocatalysis.

No abstract

The prospect of aqueous polyethyleneimine-capped CdS quantum dots (QDs), in toxic metal-ion sensing, has been explored. Pb 2+ binds strongly to the surface of the QDs facilitating ultrafast electron transfer. As a result, severe (∼90%) PL quenching is observed. Hot electron transfer plays an important role in the quenching process, as is elucidated by anticorrelation between the magnitude of ground-state bleach of the QDs and the concentration of Pb 2+ ions, as well as the concurrent decrease in bleach rise time. A second major contribution is from electron transfer from conduction band edge, with a rate constant of 1.45 × 10 11 s −1 . Selectivity in this "turn-off" sensing process is governed by the exergonicity, quality of QD surface, nature of capping ligand, and its metal-ion binding properties. Engineering these factors is crucial for the development of QD-based selective and efficient metal-ion sensors.

No abstract

The present work provides an effective methodology for controlled room-temperature aqueous synthesis of nickel oxalate (NiOX) nanosheets and nanoflakes in the presence of anion rich self-assembled bilayers of catanionic surfactant comprising of anionic sodium dodecyl sulfate (SDS) and cationic cetyltrimethylammonium bromide (CTAB). Encouragingly alteration of the CTAB/SDS ratio played an extraordinary role to form nanoflakes and nanosheets of NiOX. Our synthetic approach is combined with calcination to produce antiferromagnetic spherical and hexagonal nickel oxide (NiO) nanoparticles (NPs) as the end product.Synthesized nanostructured NiOX and NiO were characterized by X-ray diffraction study (XRD), energy dispersive X-ray spectroscopy (EDS), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). TEM studies illustrated that spherical NiO NPs have an average size around 5-10 nm and that of hexagonal NiO NPs have average width of about 22-27 nm. Temperature and field dependent magnetic properties of spherical and hexagonal NiO nanomaterials (NMs) were measured by using a SQUID magnetometer which revealed canted antiferromagnetic and spin glass nature, respectively.In addition, we report photocatalytic activity of NiO NMs, investigated on the photodegradation of phenol under ambient conditions, and as expected, the NiO having largest surface area showed best catalytic efficiency. This biomimetic catanionic surfactant inspired approach which require only metal ions as reactants have a definite potential towards an alternative, simple way of synthesizing metal oxide NMs.

No abstract

Nonionic surfactant modulated aggregation induced emission enhancement (AIEE) of Dimethyl-2,5-bis­(4-(methoxyphenyl)­amino)­terephthalate (DBMPT) has been investigated. DBMPT exhibits unidirectional aggregated growth with nonionic triton X-100 (TX-100) to produce highly luminescent nanorods, the dimensions and emission intensities of which are controlled by concentration of DBMPT. Energy transfer from perylene-3,4,9,10-tetracarboxylic acid dianhydride (PTAD) to these nanorods in aqueous medium produces pure white light emission with the CIE chromaticity coordinates (0.33, 0.36) and a significantly high quantum yield of 35%. Gelation of the system with agarose yields a bright white light emitting gel. Both these factors demonstrate an excellent potential for application of this system in light harvesting and as an advanced material for organic electronic devices.

We herein report a simple and effective soft template mediated synthesis protocol for the room temperature preparation of highly crystalline cerium (Ce 3+ ) and terbium (Tb 3+ ) doped lanthanum phosphate (LaPO 4 ) nanorods (NRs) and nanoflowers. Anionic surfactant sodium bis(2-ethylhexyl) sulfosuccinate (AOT)/n-alkane soft template was chosen since it forms stable reverse micelles (RMs). Transmission electron microscopy (TEM) analysis corroborated successful formation of LaPO 4 :Ce 3+ ,Tb 3+ NRs having different aspect ratios (ranging from 2.8:1 to 7.6:1) under varying reaction conditions. The crystalline nature of the nanomaterials (NMs) was ascertained by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and small-area electron diffraction (SAED) studies. Energy-dispersive X-ray (EDX) and Fourier transform infrared (FTIR) spectroscopy further verified the elemental existence of the desirably synthesized nanostructures. Experimental results from thermogravimetric-differential thermal analysis (TG-DTA) revealed thermal stability of the NRs up to 800 °C. The prepared NRs exhibit strong yellowish-green photoluminescence (PL) at 544 nm ( 5 D 4 → 7 F 5 ) when excited at 270 nm. Furthermore, timeresolved decay analysis along with steady-state PL measurements indicated an efficient energy transfer (ET) phenomenon between Ce 3+ and Tb 3+ ions doped in LaPO 4 (LAP) host matrix.