This PDF file contains the front matter associated with SPIE Proceedings Volume 12584, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

New compounds consisting of xanthenone and thioxanthenone derivatives are synthesized and the photophysical properties of the compounds are discussed in detail. The difference between singlet and triplet energies was obtained at 0.09 and 0.37 eV (at low temperature). Furthermore, the logarithm of the laser power versus the logarithm of the PL intensity showed a slope of less than 1, and the compounds exhibit thermally activated delayed fluorescence (TADF). In addition, the photoluminescence quantum yield of the spin-coated films was gained 51.83 and 41.22%, respectively. The powder X-ray diffraction of the grinded (under the force) compounds and also the PL spectrum of the compounds were shifted and the compounds were mechanochromic when the color of the compounds was changed. The ionization potential of the compounds showed (5.49 and 5.62 eV) that the compounds were well suited for using in the fabrication of OLED devices as an emitter layer. The performance of the OLEDs was investigated and the maximum brightness and external quantum efficiency were found to be 44573 cdm^-2 and 12.61%, respectively.

Interface effects in metals-semiconductors heterojunctions are subject of intense research due to the possibility to exploit the synergy between their electronic and optical properties in next-generation opto-electronic devices. In this framework, understanding the carrier dynamics at the metal-semiconductor interface, as well as achieving a coherent control of charge and energy transfer in metal-semiconductor heterostructures, are crucial and yet quite unexplored aspects. Here, we experimentally show that thermionically injected carriers from a gold substrate can drastically affect the dynamics of excited carriers in bulk WS₂. By employing a pump-push-probe scheme, where a push pulse excites direct transitions in the WS₂, and another delayed pump pulse induces thermionic injection of carriers from the gold substrate into the semiconductor, we can control both the formation and annihilation of excitons. Our findings might foster the development of novel opto-electronic approaches to control charge dynamics using light at ultrafast timescales.

In this work we present mechanically induced Long Period Gratings (LPGs) realized in different kinds of glass optical fibers by using UV-cured 3D printed periodic grooved plate. The periodic modulation of the geometry and refractive index along the length of the optical fiber is induced by pressure applied transversely to the grooved plate and leads to light coupling between the core mode and co-propagating cladding modes at specific resonance wavelengths. Using the proposed method, we realize and analyze in detail the behavior of the gratings induced in different optical fibers (i.e., SMF-28 and two different double cladding fibers), with and without acrylate coating. Results confirm that the depth of the attenuation bands in the transmission spectrum of the gratings, which were induced by gradually increasing the applied load show high tunability in the range of 1400-1650 nm with the maximum depth of 24 dB. Among the methods used for the fabrication of LPGs, the one studied here is reversible, very low cost, easy to tune, compatible with different kind of fibers and does not require a specific preparation of the fiber. The obtained devices are potentially useful for several application spanning from filters to sensors.

In the last decade, smart materials have been developed in the fields of optical machines, sensors, motors, robots, and energy harvesting. This is due to their capability to respond to external stimuli or environmental changes. Among smart materials, photo-mobile polymers (PMPs) based on liquid crystals are the most promising in the field of photo-responsive actuators. These polymers are made with a mixture of liquid crystals containing azobenzene moieties that can undergo photoisomerization from trans to cis under UV light. This process leads to a macroscopic bending of the PMPs, which transforms light into mechanical energy. To enhance the PMPs' actuation, a novel liquid crystal nanocomposite is proposed. In our work, the nanocomposites are prepared with different concentrations of ZnO nanoparticles (NPs) embedded in the cross-linked polymer matrix. We have demonstrated that ZnO NPs improve the actuation and mechanical properties of the PMP, and the main aim of this assay is to optimize such effect as a function of the nanoparticles concentration. We also show the lowest and highest amounts of ZnO needed to enhance the bending behavior of the PMP. Optical, mechanical, and thermal analyses were performed to characterize the PMPs. Spectral characterization in UV/vis range of the bare and doped films, optical and atomic force microscopy, were used to comprehend the role of ZnO nanoparticles and their distribution among the liquid crystals. To study the dynamic response of the PMPs and their mechanical properties, lasers at different wavelengths were used.

Piezoelectric thin films are widely used in MEMS and NEMS actuators and resonators, but also in mechanical sensors and energy harvesters for IoT applications and Wireless Sensors Networks. Nanotechnology involving piezoelectric materials is a key research direction, with benefits expected from nanostructuring and the replacement of toxic materials. Piezoelectric nanocomposites based on semiconducting nanowires (NWs) are an alternative to thin films with nanostructuration benefits, such as low temperature fabrication and higher flexibility than thin films. In addition, they exhibit larger piezoelectric coefficient than their thin films counterparts. In this work we study the piezoelectric performance of vertically grown ZnO NWs based on Finite Element simulations in the PFM (Piezoresponse Force Microscopy) configuration. In this AFM (Atomic Force Microscope) mode, the AFM tip is placed in contact with the top surface of the NW while applying a voltage, thus inducing a deformation of the structure by the reverse piezoelectric effect. Different parameters are assessed: the effect of the surrounding air, the NW size and geometry and the effect of the semiconducting properties, in particular the doping level and surface traps density. The results are compared to previous theoretical approaches and experimental findings.

The recent progresses made in the manufacturing of new plasmonic photomobile films are offering innovative solutions for light induced motion actuators and devices. Indeed, such films can be assimilated as transducers thanks to their ability to convert light into displacement with strokes up to several millimeters. By adjusting the incident light parameters (wavelength, exposure time…) the photomobile films actuation can be controlled to answer many applications requesting high displacements and low forces. In these regards, the behaviour of the photomobile films were characterized prior to their integration in more complex devices. Then, several proof-of-concepts of these devices were manufactured to try to bring new functionalities to the market such as light driven optical switch, optical micro-valve, and deflector: The optical switch features interesting properties in term of electrical insulation by eliminating the dark currents responsible for noise in image sensors. It also exploits the large stroke of the photomobile films to achieve the standard electrical insulation distance versus emitter voltage. Light driven micro-valves/micro-pumps are suitable for delivering a small quantity of fluids with high precision for example in medical devices. Using this technology, a fluid circuit can be opened and closed when light is switched from on to off (or inversely) without embedded electric power. Optical deflectors are used widely in optical pointing applications where fast responses and/or high precisions are critical. An appropriate understanding of the photomobile films behaviour enables to control the direction of the beam deflection within large angular ranges.

Rapid growth is promoting the Internet of Things (IoT) to become one of the main branches of the semiconductor industry. Surprisingly, the IoT growth would have been even faster if economically attractive and reliable alternatives for batteries and wires had been available. Providing power supply to the IoT nodes is challenging regarding their: (i) quantity (close to 8x the human population), (ii) harsh operation environments, (iii) size (typical footprint much smaller than mm²) and (iv) hard-to-reach locations. Modern IoT node requires very small energy (less than 100μJ/cycle) to operate. Wire supply of energy is expensive and uncomfortable while using a battery requires periodic replacements/maintenance and produces tons of toxic waste. Energy Harvesting (EH) could be a solution to overcome the IoT supply difficulties offering self-supplied nodes enabling further IoT market growth. EH converts natural or waste energies (vibrations, heat losses, light, etc.) into useful energy. We present an innovative two-step conversion harvester capable of transforming light into electricity via the PieZoelectric (PZ) effect. Our approach uses a Photo- Mobile Polymer (PMP) integrated with the PZ material. PMP serves as light-to-movement transducer and PZ converts the light-induced PMP flexions into voltage. As a PZ material, a nanostructured ZnO nanorods were used as their fabrication is cheap and ready-to-use at industrial scale. ZnO performance characterization in a dedicated flexions simulator revealed energy as high as 80nJ during 55sec bending runs. This result encourages further PMP and ZnO optimization enabling extension of piezoelectrics onto light conversion.

Azobenzene-based photo-mobile polymer (PMP) samples were mechanically coupled with foils of piezoelectric material (PZM) and placed under a solar simulator. The solar simulator used a short arc xenon lamp as a light source with an AM1.5 filter o mimic the absorption spectrum of earth’s atmosphere. This setup, commonly used for testing solar cells (at a power density of 1000W/m2), was used to verify the energy generation capabilities of a PMP-PZM system. As shown in previous works, the movement of the PMPs can be attributed to a narrow spectrum of light near the UV range while heat or light outside of that narrow band can prove detrimental to the motion. Thus, to verify operation under "natural light" various methods filters are employed to the solar simulator light. The output of the PZM was loaded with a constant resistance and the voltage across the load was measured using a high impedance buffer amplifier to eliminate any other loading effects. While it was shown that any optical filters that removed the UV component lead to completely stopping the PMP motion, the system was capable of operating in direct sunlight and generated measurable energy on the load. Peak voltage of over 4V was achieved and discharged an average of 710nJ over a 50s period. This result could be significantly improved, but was limited by the mechanical capabilities of the shutter.

Zinc oxide (ZnO) nanowires (NWs) are excellent candidates for the fabrication of energy harvesters, mechanical sensors, piezotronic and piezo-phototronic devices thanks to the interplay between piezoelectric and semiconducting properties. The growth of ZnO NWs on flexible substrates would further broaden their possible applications. However, such a growth requires low temperature synthesis to prevent any damage to the flexible polymer. Another difficulty lies in the fact that the deposition of patterned ceramic thin films on flexible substrates is challenging, especially under vacuum free conditions. In this framework, printing technologies like inkjet and gravure printing have a noteworthy potential since they allow to deposit thin films onto flexible substrates and offer several other advantages like cost efficiency, use of low temperatures, vacuum-free processing, high throughput and the possibility of patterning during the deposition process. In this work, we report the chemical bath deposition (CBD) growth of high quality ZnO NWs on polyethylene terephthalate (PET) starting from inkjet printed seed layer constituted of ZnO nanoparticles and a comparison with that obtained with seed layer deposited by gravure technology. Using Piezoresponse Force Microscopy (PFM), we observed that the Zn-polar domains are homogeneously distributed at the top surface of the grown ZnO NWs. This work demonstrates the key benefit of the printing techniques over conventional methods (e.g. Atomic Layer Deposition, ALD) to deposit seed layers at low temperature on flexible substrates. This opens the possibility of manufacturing completely vacuum-free solution-based flexible piezoelectric devices.

In this work, we developed and characterized composites prepared by dispersing conductive carbon black (CB) at different concentrations in an azobenzene-based photomobile polymer (azo-PMP) matrix. This polymer can move under UV-blue light because its azobenzene moieties undergo a reversible photoisomerization from trans to cis configuration and this nanoscopic structural movement induces a macroscopic movement in the film. We studied the possibility to modify the photomobile properties of azo-PMP by introducing different concentrations of CB (from 0wt.% up to 1wt.%) and we investigated morphology, optical properties and photomobile behaviour at different wavelengths. Optical analysis by polarized light shows that the films with CB concentrations up to 0.1wt.% are quite homogeneous and still present birefringence properties. Photoresponsivity measurements at wavelengths in the range 457-747nm were studied to investigate how the presence of the CB affects the photomobile response inside and outside the absorption spectral region of azo-polymers. Choosing appropriately the CB concentration, we demonstrated that it is possible to enlarge the usable spectral bandwidth of the samples in visible region towards the visible and near infrared spectral region.

The study of optical properties of various photonic band gap (PBGs) structures, focused on the in-plane propagation of 2D-PCs PBGs which are most applied in micro-fabrication and optical integration. These devices provide many novel and useful properties, such as lossless confinement of light mode, high-Q microcavity, linear waveguiding in low index material, low-loss bending, high efficiency resonant tunneling process to transfer energy between defects etc. The parameter interplay on the band gap formation is discussed first, then light modes in ideal bulk PCs are investigated.as finally, interaction between defects crucial to planar device designs. The comparison between the slab with air holes as with microcolumns confirmed that the surface recombination will be smaller in columns as that in air holes when assuming a constant filling factor of semiconductor. The photonic crystals in a square or hexagonal lattice as air holes on silicon on insulator (SOI) layers obtained bandgap centered on the wavelength of 1.55 μm, the spectral region for optical communications. By applications of computational methods like Finite Difference Time Domain (FDTD) could be determined the bandgap of the structure and computed transmission and reflection properties of system.

Imitating the self-regulated motions of natural species allows for novel applications in inanimate material systems. These applications include autonomous robotic systems, adaptive devices, and auto-energy harvesting. However, significant challenges exist in accurately controlling stimulus-induced deformations and establishing a reliable relationship between external energy fields and material deformations. In this study, we demonstrate that a simple light-triggered bending actuation in smart material systems based on liquid crystal elastomers is influenced by an opto-mechano-optical feedback mechanism. The pre-curved geometry enables enhance of light absorption upon photothermally induced deformation (from bent to flat), followed by a reduce of energy absorption upon further deformation (from flattening to bending toward the light). This strong nonlinearity in stimulus-induced deformability is governed by positive and negative feedback, and we experimentally verified these mechanisms using a thermal camera. Our results reveal the ubiquitous feedback nature of most light-active polymer systems.

Numerous efforts have been recently undertaken towards the development of rectifying devices operating at high frequencies especially dedicated to light harvesting and photo detection applications. To this end various rectification strategies have been implemented, such as laser-induced STM tunneling, metal-insulator-metal (MIM) travelling wave diodes, plasmonic nanogap optical antennas, antenna-diode coupled planar MIM, and MIM point-contact sharp-tip or whisker diodes. However, developing high frequency rectifying antennas (rectennas) remains a major technological challenge, as only recent progresses enabled the fabrication of efficient tunable nano-antennas at near infrared and visible frequencies. Here we report on a new type of rectenna based on plasmonic carrier generation. The proposed rectifying structure consists of a broadly resonant gold conical nano-tip antenna in contact with a metal-oxide/metal sample surface, forming a point-contact tunneling diode. The nano-sized antenna apex, designed to maximize the Surface Plasmon Polaritons (SPPs) damping, allows for an efficient power conversion from the light field into excited charges above the Fermi level, the latter ones collectable from the point-contact location through an electronic tunneling process. We demonstrated rectification operation at 280 THz with a power conversion efficiency one order of magnitude higher than the state-of-the-art which we attribute to efficient plasmonic carrier generation and collection.

Nanodiamonds (NDs) have attracted great interest due to their high refractive index and thermal conductivity. The unique properties of NDs, including high thermal conductivity, chemical stability, and tensile strength, make them a promising candidate for enhancing OLED efficiency. NDs were coated either beneath or above the PEDOT:PSS hole injection layer in a green-emitting OLEDs (ITO/ PEDOT:PSS/NPD/CBP:Ir(ppy)3/TPBi/Liq/Al). The best performance is obtained from the device with NDs layer beneath the PEDOT:PSS layer where the current efficiency (CE) is increased by 5.4%, power efficiency (PE) is increased by 17.7% and the external quantum efficiency (EQE) is increased by 4.5% at a luminance of 10000 cd/m² as compared to a standard device without NDs layer.

We propose plasmonic switches based on nanoantennas with fractal features on top of vanadium dioxide (VO₂) thin films. These plasmonic switches can be devised by utilizing various kinds of fractals like – the Sierpenski fractal or the Koch fractal. When exposed to heat, voltage, or infrared radiation, the VO₂ thin film undergoes a phase transition from its insulator state to its metal state, thus leading to switching in the total optical behavior of the proposed switch. In this paper, the switching performance characteristics of the near-field plasmonic switches (NFPS) are numerically analyzed. As the iterations of the fractal features of the switch are increased, the electric-field intensity is enhanced during ON state of the NFPS and the electric-field intensity is reduced during OFF state of the NFPS. We also employ Finite Difference Time Domain (FDTD) analysis to numerically analyze the VO₂ layer thickness effect on the performance of the NFPS. These plasmonic switches possess the potential to be used as elementary switching devices in computing networks and optical communication networks.

In the present research work, a Dy³⁺ doped Tungstate phosphor that emits light in white region has been synthesized using conventional solid-state reaction. An X-ray diffraction (XRD) pattern for the as-synthesized phosphor material was recorded for structural analysis and phase identification. The diffraction peaks of the tungstate phosphor match very well with the standard JCPDS pattern. The optical band gap value of the as-synthesized phosphor has been measured using diffuse reflectance spectra (DRS). The photoluminescence (PL) spectral features recorded for the Dy³⁺ ions activated tungstate phosphor under 360 nm excitation reveal strong emission peaks in blue (490 nm), a relatively less intense peak in the yellow region (580 nm) and a significantly less intense red peak (683 nm). From the recorded PL spectra, the CIE chromaticity coordinates (0.33046, 0.37422) estimated for 1.0 mol% doping concentration of Dy³⁺ ions in the as-prepared phosphor material are falling in the white region. CCT value (5580K) signifies its application for cool white light-emitting diode (w-LEDs). The PL decay spectral profile recorded at 480 nm emission under 360 nm excitation shows double exponential behaviour. The temperature-dependent PL (TDPL) measurements demonstrate relatively better thermal stability for the as-synthesized phosphor. All the investigations carried out finally allow us to contemplate the suitability of Dy³⁺ ions doped tungstate phosphor for w-LED.

Organic solar cells (OSCs) are characterized by their low cost, flexibility, compact size, and solution processing. OSCs are created utilizing a nontoxic technology that employs bulkhetrojunction (BHJ) structures. The photo conversion efficiency (PCE) of OSCs has been boasted in the last decades. BHJ fullerene-based OSCs have low open-circuit voltages and poor photo absorption. In this study, the recent non-fullerene acceptor (Y6), which has an electron-deficient core-based central fused ring, has been used. The promising PM6:Y6 material is used as an active layer in the proposed OSCs. The light trapping of the OSCs is enhanced by embedding plasmonic nanoparticles (NPs) in one of its layers. This could be a long-term approach to collecting more light in the photoactive layer. Au and Ag NPs have been employed the most in plasmonic OSCs. They improve PCE due to their plasmonic properties, strong localized surface plasmonic resonance (LSPR) in the visible region of the light spectrum, on-toxicity, and oxidation resistance, although Ag NPs are prone to oxidation. However, they have high costs and thermal instability. Alternative plasmonic materials such as refractory metals with high melting temperatures exceeding 2000°C and high thermal and chemical stability are employed in this work holding a comparative study between them.

Films based on a composite of a liquid crystal polymer (LC-POL) with acrylic backbone and carbon black (CB) were manufactured and characterized to develop a new smart material able to move under light. In detail, the effect of 0.1wt% of CB, a high absorption and thermal conductive filler, on morphological, optical and photomobile properties was investigated and compared with pristine LC-POL films. To study photomobile behaviuor the films were irradiated with 457nm-laser at different powers and the responses to these stimuli were compared in terms of bending angle and response time. The work shows that the presence of CB induces photomobile properties in an inactive LC polymer matrix and the mechanical response under light is fast and reversible.

The optical effects were obtained by three different ways, which are opal structures, laser polymerizing and plasmonic ultrathin Ag films deposition. Opal structures were realized by deposition of a thin layer composed of sub-micron spheres of polystyrene on the surface of an optical fiber using drop-drying method and capillary method. Multiple diffraction gratings have been designed and obtained on mechanically processed optical fiber, through means of Two-Photon Polymerization via laser direct writing (3D Lithography - 3DL). Ultrathin Ag films of 1 to 9 nm thickness were deposited by RF Magnetron Sputtering onto different substrates.