Zinc oxide is synthesised at low temperature (80°C) in nanosheet geometry using a substrate-free, single-step, wet-chemical method and is found to act as a blue-white fluorophore. Investigation by atomic force microscopy, electron microscopy, and X-ray diffraction confirms zinc oxide material of nanosheet morphology where the individual nanosheets are polycrystalline in nature with the crystalline structure being of wurtzite character. Raman spectroscopy indicates the presence of various defects, while photoluminescence measurements show intense green (centre wavelength approximately 515 nm) blue (approximately 450 nm), and less dominant red (approximately 640 nm) emissions due to a variety of vacancy and interstitial defects, mostly associated with surfaces or grain boundaries. The resulting colour coordinate on the CIE-1931 standard is (0.23, 0.33), demonstrating potential for use as a blue-white fluorescent coating in conjunction with ultraviolet emitting LEDs. Although the defects are often treated as draw-backs of ZnO, here we demonstrate useful broadband visible fluorescence properties in as-prepared ZnO.

Zinc interstitials and their complexes with oxygen vacancies, harbouring a lone pair of electrons, have been discussed as suspects for an n-type character and the ensuing conductivity of nominally undoped ZnO. ZnO nanorods, with different Zn concentrations, have been studied using photoluminescence and photoluminescence excitation spectroscopy to evidence the presence of defect states, their correlation with excess Zn and their viability as donors. It is shown that each sample may emit intense violet-blue, green-orange and red emissions, as decided by the excitation energy and presence of excess Zn. Intensity variation of these individual emissions vis-à-vis their excitation energies, in the range 4.0–2.7 eV, indicates the presence of defect states not only within the band gap but crucially within the conduction band itself, but only in a Zn rich environment. The study provides the experimental signature of the theoretical predictions of the latter states and demonstrates why Zn interstitials may be responsible for the n-type doping and conductivity of ZnO. The origin of the emissions, their interdependence and tunability are further discussed.

Photoresponse of n-type indium-doped ZnO and a p-type polymer (PEDOT:PSS) heterojunction devices are studied, juxtaposed with the photoluminescence of the In-ZnO samples. In addition to the expected photoresponse in the ultraviolet, the heterojunctions exhibit significant photoresponse to the visible (532 nm). However, neither the doped ZnO nor PEDOT:PSS individually show any photoresponse to visible light. The sub-bandgap photoresponse of the heterojunction originates from visible photon mediated e-h generation between the In-ZnO valence band and localized states lying within the band gap. Though increased doping of In-ZnO has limited effect on the photoluminescence, it significantly diminishes the photoresponse. The study indicates that optimally doped devices are promising for the detection of wavelengths in selected windows in the visible.

Epsilon near zero (ENZ) materials exhibit strongly confined optical modes and plasmonic response around and beyond the ENZ wavelength (λ_ENZ). In order to exploit the novel properties of ENZ materials for real-world applications, it is important to develop material platforms that offer continuous tuning of λ_ENZ. We report octave span, controllable, and reversible tuning of λ_ENZ from 1280 nm to 2900 nm in commercially available thin films of indium tin oxide (ITO), employing a low temperature annealing protocol. Electrical, spectroscopic, and optical measurements establish the physical basis of the observed tunability in free electron density by over an order of magnitude and quantify the real and imaginary components of the refractive index for ITO thin films. Excitation of surface plasmon polaritons (SPPs) in the metallic regime of ITO probes its infrared plasmonic response demonstrating continuous tunability of SPP frequency and crossover to the tunable ENZ plasmon mode in ultrathin films. Finally, dispersion tuning of optical fiber modes by optical coupling with a tunable λ_ENZ platform is demonstrated by investigating modal interference in a tapered silica fiber in contact with various custom tuned ITO films.

We report investigation of non-linear electronic transport through artificial grain-boundary junctions made on epitaxial films of ${\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_3$ on bicrystal ${\mathrm{SrTiO}}_3$ substrates. The experiments carried out over the temperature range 4.2 K–300 K in magnetic field up to 3 T allow us to identify some of the conduction mechanisms that may give rise to nonlinear transport in these grain boundary junctions. The nonlinear transport is associated with multistep inelastic processes in the grain-boundary region, which is moderately affected by the applied magnetic field. However the primary effect of the magnetic field is to enhance the zero-bias conductance $\left[G_0{=(dI/dV)\mathrm{}}_{V=0\mathrm{}}\right].$ The dominant voltage dependent contribution to the dynamic conductance $\mathrm{}(G=dI/dV)\mathrm{}$ comes from a term of the type $V^{4/3}$ at lower temperatures. Other voltage dependent contributions to G, which are of higher order in V, appear only for $T>~75\mathrm{K}.$ In addition we found a contribution to G arising from a $V^{0.5}$ term, which is likely to arise from the disordered region around the grain boundary (GB). The magnetoresistance in the GB depends on the bias used and it decreases at higher bias. The bias dependence is found to be reduced as temperature is increased. We discuss the physical origins of the various contributions to the nonlinear conduction.

Kinetochore couples chromosome movement to dynamic microtubules, a process that is fundamental to mitosis in all eukaryotes but poorly understood. In vertebrates, spindle-kinetochore-associated (Ska1–3) protein complex plays an important role in this process. However, the proteins that stabilize Ska-mediated kinetochore-microtubule attachment remain unknown. Here we show that microtubule plus-end tracking protein EB1 facilitates Ska localization on microtubules in vertebrate cells. EB1 depletion results in a significant reduction of Ska1 recruitment onto microtubules and defects in mitotic chromosome alignment, which is also reflected in computational modelling. Biochemical experiments reveal that EB1 interacts with Ska1, facilitates Ska1-microtubule attachment and together stabilizes microtubules. Structural studies reveal that EB1 either with Ska1 or Ska complex forms extended structures on microtubule lattice. Results indicate that EB1 promotes Ska association with K-fibres and facilitates kinetochore-microtubule attachment. They also implicate that in vertebrates, chromosome coupling to dynamic microtubules could be mediated through EB1-Ska extended structures.