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In this Letter, we report for the first time, to the best of our knowledge, the anisotropic optical response in a graphene oxide (GO)-gold (Au) nanohybrid. Polarization-sensitive nonlinear optical absorption measurements revealed that nanohybrids are highly anisotropic, ( β ⊥ − β ‖ ) ≈ 28 c m / G W , which is more than one order of magnitude higher than that of control GO (2 cm/GW). The first-principle analysis of absorbance at nanohybrid interfaces with varying functional ligand concentrations corroborates with the experimentally observed intrinsic linear anisotropy. Thus, this Letter enables new routes to realize smart and high-performing nonlinear optical systems selectively and directionally such as tunable optical limiters and optical data processing devices.

Two-dimensional (2D) covalent organic frameworks (COFs) are an emerging class of porous materials with potential for wide-ranging applications. Intense research efforts have been directed at tuning the structure and topology of COF, however the bandgap engineering of COF has received less attention, although it is a necessary step for developing the material for photovoltaic or photonic applications. Herein, we have developed an approach to narrow the bandgap of COFs by pairing triphenylamine and salicylideneaniline building units to construct an eclipsed stacked 2D COF. The ordered porous structure of 2D COF facilitates a unique moisture-triggered tautomerism. The combination of donor–acceptor charge transfer and tautomerization in the salicyclidineaniline unit imparts a large bandgap narrowing for the COF and turns it color to black. The synthesized COF with donor–acceptor dyad exhibits excellent nonlinear optical properties according to open aperture Z-scan measurements with 532 nm nanosecond laser pulses.

Manipulating optical nonlinearity is a very fascinating prospective for both fundamental and technological purpose; offers a potential platform to explore the saturable absorption (SA) to the nanoscale limit. In this manuscript, we have focused on the tunable wavelength and pulse width dependent ultrafast broadband SA of Sb2Se3 nanowires in the resonant and the above bandgap excitations of 120 fs and 7 ns pulses. In this context, we numerically simulated the SA of Sb2Se3 nanowire with a two-level model. The solutions of the coupled rate equations for a Gaussian shaped pulse exactly reproduced the experimental results in both temporal and spatial domains. Our model provides a precise spacio-temporal analysis of carrier populations of each photo-excited state in the system. Moreover, excited state decay time (1.5 ns) and the ratio of excited state absorption cross section (σes) to the ground state absorption cross section (σgs) is less than unity for 1-D Sb2Se3 nanowires. Hence, Sb2Se3 nanowires can be employed as passive mode-lockers and essential photodetectors for ultrashort pulsed laser and can be tuned by wavelength and pulse width. These observations advise a remarkable nonlinear optical response which is expected to be comparable or even better than the graphene and 2D TMDC’s (MX2) like MoSe2, MoS2, WSe2, WS2 etc.

The nonlinear optical absorbance of conventional materials is very weak, yet its magnitude dominates device performance in, for example, optical limiting and pulse shaping. Therefore, achieving a strong nonlinear optical response is a longstanding goal. The authors propose charge transfer between donor and acceptor materials as a means to greatly enhance nonlinear response, toward the realization of high-performance optical limiters. Excellent agreement between experiment and theory for a test hybrid material validates the idea, and guides the design and fabrication of an actual liquid-cell-based absorptive optical limiter, which outperforms benchmark devices.

Metal nanoparticle-semiconductor interfaces are sites of complex light-matter interactions, in particular, the exciton-plasmon coupling which plays a key role in the optical response of such heterostructures. There exists a pathway of photoinduced charge transfer from the semiconductor to the metal, which can be used to controllably vary the driving forces at the interface that leads to tunable optoelectronic properties. In this letter, we report the observation of a dramatic suppression of plasmonic as well as excitonic absorption in a-Ge24Se76/gold nanoparticle heterostructures by trapped charges. Suppression of the excitonic absorption is strongly correlated with the plasmon wavelength. (C) 2016 Author(s).

Organic Light Emitting Diodes (OLED) are receiving increased attention due to tremendous application potential these devices hold in the areas of large area displays and lighting applications. However, the problems of efficiency, stability and shelf life are major challenges for making OLEDs an attractive alternative. The simple device structure involving anode, emissive layer and cathode is no longer the norm. Recently, various buffer layers like Hole Injection Layer (HIL), Hole transport Layer (HTL), Electron Injection Layer (EIL), Electron Transport Layer (ETL) etc. are being widely used as integral parts of the OLED architecture to enhance the performance parameters. The nomenclature of these layers is often confusing and sometimes used by different authors to mean different layers and a common and universal nomenclature for layers is still wanting. Applying a buffer layer, often called as the hole injecting layer (HIL) between anode and emissive layer is a general technique for increasing the efficiency and stability of organic light emitting diodes. Poly- (3,4-ethyhylene dioxythiophene): poly- (styrenesulphonate) (PEDOT:PSS) is a very common and popular such HIL used in OLEDs. In this chapter, a basic structure of OLEDs has been discussed in perspective with this HIL material and the effect of annealing this PEDOT: PSS layer on the characteristics of the device at different temperatures ranging from 100°C to 300°C in vacuum. Devices fabricated in clean room conditions are characterized for their electrical and optical properties. Equivalent circuits of the devices are deduced using impedance spectroscopy and discussed. Surface morphology of the HIL layers using atomic force microscopy (AFM) provides reasons for the variation of the device properties with the annealing of HIL.

In this paper, we report that the non linear behavior of amorphous As2S5 can be drastically altered from two photon absorption (TPA) to saturable absorption (SA) when it form heterostructures with Au nanoparticles (ANPs).

Organic memory devices are one of the active research areas. Iodine doped rubber with fullerene C60 molecules are studied for memory application. The device fabrication is carried out by simple solution processing technique, Current voltage characteristics of the device is having a hysteresis with a negative differential resistance. Write-read-erase cycle is performed, which reveals the potential use of the device as a low power consuming non volatile memory.

One-dimensional (1D) free-standing nanowires are particularly important for carrier confinement in two dimensions, which provides a platform to explore the nonlinear optical phenomena at the nanoscale. In this Letter, we demonstrate saturable absorption in the resonant and above-bandgap excitations of both ns and fs pulses in 1D crystalline Sb2Se3 nanowires prepared by the facile hydrothermal method. Impressively, the average length of the nanowires extends to a few micrometers with a high aspect ratio of 300. The excited-state to ground-state absorption cross-section ratio in Sb2Se3 nanowires is ≈0.23, which suggests that they can be utilized as passive mode lockers.

Consequent to the fast increase in data storage requirements new materials and device structures are explored in a war footing. Organic memory devices are attracting lot of interest among the researchers and are becoming a hot topic of investigations. This study is an attempt to develop a tri‐layer organic memory device using indium tin oxide (ITO) nanoparticles as charge trapping middle layer between tris‐8(‐hydroxyquinoline)aluminum (Alq3) layers employing spin coating technique. Device switching is studied by applying a current‐voltage (I‐V) sweep. On increasing the applied bias the device switched from the initial high resistance (OFF) state to a low resistance (ON) state at a switch on voltage of around 4 V. ON/OFF ratio is of the order of 100 at a read voltage of 2 V. The device is found to remain in the low resistance state on further scans, showing the applicability of this device as a write once read many times (WORM) memory.

In this Letter, we report for the first time, to the best of our knowledge, continuous-wave laser background illumination (BGI) as a simple and yet useful tool to tune nanosecond transient absorption (TA) in a-Ge25As10Se65 thin films. In our experiments, we observed remarkable blueshift in TA as a function of the BGI intensity. Strikingly, relaxations of TA in background-illuminated samples are much faster than the as-prepared samples. This observation provides new insights into the bond-breaking mechanism. Further, decay time constants of TA are wavelength dependent, which signifies that excited carriers have a longer lifetime in deep traps than in shallow traps.