A. K. Kole

Ethylenediamine assisted synthesis of wurtzite zinc sulphide nanosheets and porous zinc oxide nanostructures: near white light photoluminescence emission and photocatalytic activity under visible light irradiation

Porous fungus-like ZnO nanostructures have been synthesized by simple thermal annealing of the hydrothermally synthesized sheet-like ZnS(en)0.5 complex precursor in air at 600 °C. Structural and morphological changes occurring during ZnS(en)0.5 → ZnS → ZnO transformations have been observed closely by annealing the as-synthesized precursor at 100–600 °C. Wurtzite ZnS nanosheets and ZnS–ZnO composites are obtained at temperatures of 400 °C and 500 °C, respectively. Thermal decomposition and oxidation of the ZnS(en)0.5 nanosheets have been confirmed by differential scanning calorimetry and thermo-gravimetric analysis. The visible light driven photocatalytic degradation of methylene blue dye has been demonstrated in the synthesized samples. ZnS–ZnO composite shows the highest dye degradation efficiency of 74% due to the formation of surface complex as well as higher visible light absorption as a result of band-gap narrowing effect. The porous ZnO nanostructures show efficient visible photoluminescence (PL) emission with a colour coordinate of (0.29, 0.35), which is close to that of white light (0.33, 0.33). The efficient visible PL emission as well as visible light driven photocatalytic activity of the materials synthesized in the present work might be very attractive for their applications in future optoelectronic devices, including in white light emitting devices.

Room temperature synthesis of Mn2+ doped ZnS d-dots and observation of tunable dual emission: Effects of doping concentration, temperature, and ultraviolet light illumination

Mn2+ doped (0-50.0 molar %) ZnS d-dots have been synthesized in water medium by using an environment friendly low cost chemical technique. Tunable dual emission in UV and yellow-orange regions is achieved by tailoring the Mn2+ doping concentration in the host ZnS nanocrystal. The optimum doping concentration for achieving efficient photoluminescence (PL) emission is determined to be similar to 1.10 (at. %) corresponding to 40.0 (molar %) of Mn2+ doping concentration used during synthesis. The mechanism of charge transfer from the host to the dopant leading to the intensity modulated tunable (594-610 nm) yellow-orange PL emission is straightforwardly understood as no capping agent is used. The temperature dependent PL emission measurements are carried out, viz., in 1.10 at. % Mn2+ doped sample and the experimental results are explained by using a theoretical PL emission model. It is found that the ratio of non-radiative to radiative recombination rates is temperature dependent and this phenomenon has not been reported, so far, in Mn2+ doped ZnS system. The colour tuning of the emitted light from the samples are evident from the calculated chromaticity coordinates. UV light irradiation for 150 min in 40.0 (molar %) Mn2+ doped sample shows an enhancement of 33% in PL emission intensity

Observation of nonlinear absorption and visible photoluminescence emission in chemically synthesized Cu2+ doped ZnS nanoparticles

Nonlinear optical properties of chemically synthesized ZnS and Cu2+ doped ZnS nanoparticles of average sizes ∼2.5 nm are reported by using open aperture z-scan technique with the Nd:YAG laser second harmonic radiation at 532 nm. Tunable photoluminescence emissions in the visible region due to the increase in concentration of Cu2+ doping in ZnS are observed at room temperature. By analyzing the experimental z-scan data, it is found that three photon absorptions (3PA) are taking place in all the samples. The extracted values of 3PA coefficients of the samples are ∼109 times higher than that of bulk ZnS.

Enhanced nonlinear optical properties of graphene oxide–silver nanocomposites measured by Z-scan technique

Nonlinear optical properties (NLO) of a graphene oxide–silver (GO–Ag) nanocomposite have been investigated by the Z-scan setup at Q-switched Nd:YAG laser second harmonic radiation i.e., at 532 nm excitation in a nanosecond regime. A noteworthy enhancement in the NLO properties in the GO–Ag nanocomposite has been reported in comparison with those of the synthesized GO nanosheet. The extracted value of third order nonlinear susceptibility (χ3), at a peak intensity of I0 = 0.2 GW cm−2, for GO–Ag has been found to be 2.8 times larger than that of GO. The enhancement in NLO properties in the GO–Ag nanocomposite may be attributed to the complex energy band structures formed during the synthesis which promote resonant transition to the conduction band via surface plasmon resonance (SPR) at low laser intensities and excited state transition (ESA) to the conduction band of GO at higher intensities. Along with this photogenerated charge carriers in the conduction band of silver or the increase in defect states during the formation of the GO–Ag nanocomposite may contribute to ESA. Open aperture Z-scan measurement indicates reverse saturable absorption (RSA) behavior of the synthesized nanocomposite which is a clear indication of the optical limiting (OL) ability of the nanocomposite.

Observations of unusual temperature dependent photoluminescence anti-quenching in two-dimensional nanosheets of ZnS/ZnO composites and polarization dependent photoluminescence enhancement in fungi-like ZnO nanostructures

Hybrid semiconductor nanostructures which integrate the favourable characteristics of both the component materials are found recently to be attractive candidate materials for research investigations having interesting optical properties. Considering the fact that the temperature of the materials used in photo-luminescent devices may vary while using them in a real device, it is essential to study the performances of such materials at variable temperatures. But the photoluminescence (PL) emission capabilities of such materials above room temperatures have not been well investigated, yet. However, in this work we have reported temperature dependent unusual PL emission characteristics of 2D nanosheets of ZnS/ZnO composite in the temperature range of 273–333 K. The composite sample has been produced by annealing the organic-inorganic ZnS(ethylenediamine)0.5 nanosheets, which are obtained by solvothermal technique. The as-synthesized nanosheets and another thermally annealed product of ZnO nanostructures showe...

Mn2+ doped ZnS quantum dots in ferroelectric liquid crystal matrix: Analysis of new relaxation phenomenon, faster optical response, and concentration dependent quenching in photoluminescence

Phase transitional, dielectric, electro-optical, polarizing optical microscopic, photoluminescence (PL), and Fourier transformed infrared (FTIR) spectroscopic measurements have been carried out on ZnS:Mn quantum dots (QDs) dispersed ferroelectric liquid crystal (FLC). A new dielectric relaxation mode has been envisaged in FLC material due to the presence of 0.25 wt. % ZnS:Mn (40 mol. %) QDs. The characteristics of the new mode have been compared with those of the soft mode. A significant fastening of the electro-optical response (∼75%) has been observed in the case of 0.25 wt. % ZnS:Mn (20 mol. %) QDs doped FLC material. The induction of the new relaxation mode is attributed to the flexoelectric tilt fluctuations. The induced flexoelectric polarization in the FLC medium at the vicinity of QDs might be responsible for the enhanced spontaneous polarization in the FLC/QDs mixtures. Quenching in PL for the FLC/QDs mixtures has been observed, which strongly depends on Mn content in QDs. The change in FTIR spec...

Synthesis of anisotropic nanostructures of silver for its possible applications in glucose and temperature sensing

Syntheses of anisotropic nanostructures of silver have been demonstrated by using a simple chemical synthesis route and the roles of temperature and reaction time in the anisotropic growth of the material have been reported. The role of multiple twinned particles in the anisotropic shape evolution and branching growth of synthesized silver nanostructures is demonstrated. The optical absorption and photoluminescence (PL) properties of the non-functionalized silver nanostructures have been studied in the UV–visible wavelength region and there exist two surface plasmon resonance (SPR) peaks, one called transverse surface plasmon resonance (TSPR) peak situated at smaller wavelength at ~410–415 nm, and another called longitudinal surface plasmon resonance (LSPR) peak appearing at longer wavelength at ~595–615 nm in the visible region. Intense PL emission spectra centered at ~410 nm have been observed from the synthesized products obtained at lower temperature, whereas the PL spectra of higher temperature materials are divided into two broad peaks staying >100 nm apart at both sides of 410 nm. It has been demonstrated that the synthesized non-functionalized silver nanostructure can further be utilized for sensing of glucose and temperature. Tyndall effect experiment with the synthesized silver nanostructures dispersed in methanol has been performed and demonstrated the stability of the nanostructures.

Measurement of the Nonlinear Optical properties of Silver Nanoparticles and Graphene Oxide Nanocomposite

The nonlinear optical properties of silver nanoparticle and graphene oxide (AgNP/GO) nanocomposites synthesized by solvothermal method have been measured in nanosecond time by using Z-scan technique with Q-switched Nd:YAG laser radiation of 1064 nm wavelength.

Observation of Nonlinear Optical Properties of Chemically Synthesized Cu2+ Doped ZnS Nanoparticles

ZnS and Cu2+ (0.50 and 1.00 %) doped ZnS (i.e., ZnS:Cu) nanoparticles (NPs) are synthesized by chemical co-precipitation method at room temperature. X-ray diffraction (XRD) studies and the analysis of the selected area electron diffraction pattern (SAED) obtained from transmission electron microscopy (TEM) confirmed the formation of zinc blende structure of all the synthesized samples. Irrespective of the samples, the average particle sizes, as obtained from the XRD and TEM is about 2.5 nm. The room temperature photoluminescence (PL) emission measurements revealed the presence of green emission band in all the ZnS:Cu samples which is attributed to Cu2+ incorporation in ZnS. It is found by Gaussian deconvolution of the measured PL spectra of the synthesized samples that two peaks appeared at 405 and 445 nm in undoped ZnS NPs. In addition to the above two peaks, a third peak is noted in green region for ZnS:Cu NPs, the second and third peak shows a red shift with increasing Cu2+ concentration. Three photon absorption (3PA) and nonlinear refraction (NLR) coefficients are also measured at 532 nm, the second harmonic of a Q-switched Nd:YAG laser radiation, by using the z-scan technique, viz., in 0.5 % Cu2+ doped ZnS:Cu sample. From the analysis of open aperture (OA) z-scan data it is found that three photon absorptions (3PA) is the dominant mechanism for appearance of nonlinear absorption (NLA) in the sample and the extracted value of the intrinsic 3PA coefficient is ~109 times larger than that of bulk ZnS.

Influence of Co Doping on the Structural and Optical Properties of ZnO Nanostructures

Undoped and 2.5 % Co doped ZnO nanostructures have been synthesized by simple chemical method at the temperature of 65 °C. The prepared samples are characterized by X-ray diffraction (XRD) analysis, UV–visible absorption (UV–Vis) and photoluminescence (PL) emission spectroscopy. The XRD results indicate that the synthesized ZnO powders are a pure single phase wurtzite structure and also it is found that the lattice parameter of the synthesized ZnO nanostructure varies due to Co doping. It is also found that PL emission and UV–Vis absorption peaks are red shifted due to Co incorporation in ZnO. The results confirmed that Co is incorporated as Co2+ in the core of these nanocrystals, occupying the Zn2+ sites in the wurtzite structure of ZnO. Localized selected area electron diffraction (SAED) patterns shows that the nanorods are single crystals. The UV PL emission band of doped ZnO nanorods exhibits a red shift from 382 to 386 nm, indicating a band-edge bending due to the presence of doping material in ZnO nanostructure. The defect-related PL emission band centered at 600 nm observed in undoped ZnO sample is suppressed considerably in doped nanorods, revealing the quenching of surface defects present in the synthesized materials.