: Metal nanoparticles are nanosized entities with dimensions of 1-100 nm that are increasingly in demand due to applications in diverse fields like electronics, sensing, environmental remediation, oil recovery and drug delivery. Metal nanoparticles possess large surface energy and properties different from bulk materials due to their small size, large surface area with free dangling bonds and higher reactivity. High cost and pernicious effects associated with the chemical and physical methods of nanoparticle synthesis are gradually paving the way for biological methods due to their eco-friendly nature. Considering the vast potentiality of microbes and plants as sources, biological synthesis can serve as a green technique for the synthesis of nanoparticles as an alternative to conventional methods. A number of reviews are available on green synthesis of nanoparticles but few have focused on covering the entire biological agents in this process. Therefore present paper describes the use of various living organisms like bacteria, fungi, algae, bryophytes and tracheophytes in the biological synthesis of metal nanoparticles, the mechanisms involved and the advantages associated therein.

Because of its large direct band gap of 3.37 eV and high exciton binding energy (~60 meV), which can lead to efficient excitonic emission at room temperature and above, ZnO nanostructures in the würtzite polymorph are an ideal choice for electronic and optoelectronic applications. Some of the important parameters in this regard are free carrier concentration, doping compensation, minority carrier lifetime, and luminescence efficiency, which are directly or indirectly related to the defects that, in turn, depend on the method of synthesis. We report the synthesis of undoped ZnO nanorods through microwave irradiation of an aqueous solution of zinc acetate dehydrate [Zn(CH 3 COO) 2 . 2H 2 O] and KOH, with zinc acetate dihydrate acting as both the precursor to ZnO and as a self-capping agent. Upon exposure of the solution to microwaves in a domestic oven, ZnO nanorods 1.5 μm -3 μm and 80 nm in diameter are formed in minutes. The ZnO structures have been characterised in detail by X-ray diffraction (XRD), selective area electron diffraction (SAED) and high-resolution scanning and transmission microscopy, which reveal that each nanorod is single-crystalline. Optical characteristics of the nanorods were investigated through photoluminescence (PL) and cathodoluminescence (CL). These measurements reveal that defect state-induced emission is prominent, with a broad greenish yellow emission. CL measurements made on a number of individual nanorods at different accelerating voltages for the electrons show CL intensity increases with increasing accelerating voltage. A red shift is observed in the CL spectra as the accelerating voltage is raised, implying that emission due to oxygen vacancies dominates under these conditions and that interstitial sites can be controlled with the accelerating voltage of the electron beam. Timeresolved fluorescence (TRFL) measurements yield a life time (τ) of 9.9 picoseconds, indicating that ZnO nanorods synthesized by the present process are excellent candidates for optoelectronic devices. INTRODUCTIONZinc oxide (ZnO) is a multifunctional, direct, wide band gap (E g =3.37 eV) semiconductor with a large free-exciton binding energy (~60 meV), rendering excitonic emission processes possible at or above room temperature[1,2,3]. Thus, ZnO is a promising material for UV and blue light emitting devices with several fundamental advantages over GaN, its chief competitor. It is more radiation-resistant than GaN, comparatively inexpensive, and biocompatible [4,5]. Defects in ZnO play a major role in tailoring its optical, piezoelectric, mechanical, electronic and optoelectronic properties [3]. The desired properties of ZnO nanostructures can be tuned with either native defects or foreign atom incorporated defects (doping). Intrinsic point defects in ZnO nanorods give rise to luminescence over a broad range in the visible spectrum. This enables tunable resonant emission in the visible spectral range with a pure ZnO system. Native defect engineering is favorable over doping because foreign atoms usually affe...

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The effect of defects on the functional properties of dopant-free ZnO nanocrystals has been established by recording their luminescence and magnetism.

In this work, we have developed PVDF-TrFE/BaTiO3 composite thin film-based highly sensitive ultrasound (US) and photoacoustic (PA) transducer. The synthesized nanocomposite polymer-based sensor film has been grown layer by layer on the flat surface of a 9.00 mm diameter aluminum substrate. The fabricated transducer has been tested in pulseeco mode and it shows high sensitivity with a peak-to-peak voltage 800 mV. Preliminary US and PA experiments have been performed with the aluminum block and multi-layer ink coated phantom. The central frequency of the obtained acoustic signal was found to be 44 MHz with an acoustic bandwidth of 32 MHz (72% of central frequency at -6 dB). The PA signals have been detected with the fabricated transducer and the estimated frequency spectrum shows multiple subband central frequencies varying from 17 MHz to 55 MHz. Due to its high sensitivity and broad bandwidth, the developed transducer can be used for high-resolution US and PA microscope imaging (PAI).