Drop shaped zinc oxide quantum dots and their self-assembly into dendritic nanostructures: Liquid assisted pulsed laser ablation and characterizations

Complex nanostructures and nano-assemblies have exhibited their potential application in the fabrication of future molecular machines and molecular devices. Liquid phase pulsed laser ablation is an easy, versatile, environmental friendly and rapidly growing method for the synthesis of nanostructured materials. Nanosecond pulsed laser ablation of zinc rod placed on the bottom of glass vessel containing methanol is used to produce colloidal solution of drop shaped zinc oxide quantum dots and their self-assembly into various dendritic nanostructures. UV-vis absorption, diffuse reflectance, transmission electron microscopy, and photoluminescence spectroscopy techniques are used for the optical, microscopic, structural and defect diagnosis of obtained colloidal quantum dots and their nano-assemblies. The average length, width and aspect ratio of drop shaped zinc oxide quantum dots are 6 ± 2.4 nm, 3.5 ± 1.4 nm and 1.69 ± 0.4 nm, respectively. Careful investigation of assemblies shows that most of them have linear growth, i.e. growth in longitudinal direction is higher as compared to the transverse direction with three types of classifications as (i) linear axis symmetrical branching, (ii) linear axis asymmetrical branching and (iii) curvilinear axis asymmetrical branching. Photoluminescence spectrum has emission peaks in UV, violet, blue and green spectral region corresponding to the excitonic and various defect related emissions.

.Highlights► Synthesis of drop shaped zinc oxide quantum dots and their self-assembly into novel and nice dendritic nanostructures. ► Mechanism of self-assembly based on the electrostatic attraction between the quantum dots has been manifested. ► Highly colloidal solution of drop shaped zinc oxide QDs with narrow size distribution has been reported. ► Dendritic assemblies are classifieds into three categories namely (i) linear axis with symmetrical branching, (ii) linear axis with asymmetrical branching, and (iii) curvilinear axis with asymmetrical branching. ► Ultraviolet to green broad photoluminescence is observed, which suggests its application as wide wavelength and white light source.