Optical Absorption Enhancement Research Articles

Broadband optical absorption enhancement in stacked MWCNTs array: towards new generation of solar cells

Broadband optical absorption enhancement in stacked MWCNTs array: towards new generation of solar cells

Significant enhancement of optical absorption of graphene inside a metallic optical microcavity

The increase in the optical absorption of the graphene layers above the value of 2.3% of the bare layer in vacuum is of great interest for application in opto-electronics. A monolayer graphene sheet embedded in a stacked dielectric layers has been shown to reach an absorption up to 50%. Here, we theoretically show that the absorption could be significantly enhanced to greater than 50% via boosting the environmental permeability by using an empty optical cavity. This enhancement is nearly independent on the structure of the environment around the graphene sheet, except for the dimensional parameters of the cavity. The obtained results are crucial for motional control of graphene sheets by an all-optical method.

Fabrication of Bi-doped In2S3 thin films for highly sensitive UV photodetector applications

Fabrication of highly sensitive, high-speed photodetectors, especially using cost-effective and less toxic materials, has attracted continuous attention due to their outstanding advantages. In this report, we present different properties of Bi-doped (0,1, 3, and 5 wt%) In2S3 thin films for UV photodetectors. Bi-doped (0, 1, 3, and 5 wt%) In2S3 thin films were coated on glass substrates at a temperature of 350 °C using a low-cost nebulizer spray pyrolysis method. X-ray diffraction XRD analysis confirmed the cubic phase β-In2S3 for all the deposited films and high crystallinity is obtained for 1 wt% Bi-doped film. The presence of densely packed grains in 1 wt% Bi-doped In2S3 thin film and also small grains observed for undoped In2S3 sample is evident form morphology studies. Bi doping has caused an enhancement of optical absorption and incorporation of 1 wt% of Bi3+ into In2S3 has shifted the optical band gap from 2.87 to 2.78 eV. Current − Voltage characteristics and Current–Time characterization are used to know the key parameters of the photodetectors. Among all fabricated photodetectors, the In2S3 thin film doped with 1 wt% Bi showed superior photodetector performance with calculated Responsivity (R), Detectivity (D*), and External quantum efficiency (EQE) values of 0.65 AW−1, 15 × 1010 Jones, 125 % respectively. Transient photo-response analysis showed low rise and fall time of 3.21 and 3.78 s respectively for the 1 wt% Bi-doped sample. Optimally doped In2S3: Bi (1 wt%) thin film is most suited to fabricate photo sensing-based optoelectronic devices in UV region of the spectrum.

Probing the structural, electronic and optical properties of pure and B, N, or Li substituted Cyclo-18 ring: density functional theory investigations

Employing the quantum computational approach by using the Density Functional Theory along with GGA exchange correlation functional, we have investigated the structural, electronic, and optical properties of Cyclo-18 ring containing 18 sp hybridized carbon atoms and substituted Cyclo-C17X (X = B, N, and Li) ring. The Cyclo-18 ring has two opposite π electron system that can be organized as a D9h polyynic and D18h cumulene form. Our computational simulations suggest that D9h polyynic structure is minimum energy structure. Alkali metal doping makes C18 metallic by lowering the band gap when compared to the pure C18 (5.02eV). The strength of the chemical bonding analyzed using average binding energies for the Li, B, and N substituted Cyclo-C18 ring which are −4.58 eV, −4.65 eV, and −2.83 eV respectively. The positive charges on B, N and Li and negative charges on the Cyclo-18 ring demonstrate the partial Coulomb interactions and also charge transfer from B, N, and Li to Cyclo-18 ring. It is also found that the dominant adsorption IR peak at 2049 cm−1, 1329 cm−1, and 1011 cm−1 for B, N, and Li substituted C18 ring. There is an enhancement in optical absorption in the visible region due to doping which makes the system suitable for photo-catalytic applications.

Meta-GGA study of 2D AlN/BN planer heterostructure and performance enhancement via strain engineering.

The 2D AlN/BN planer heterostructure is a promising wide band gap semiconductor, but systematic studies of its bandgap and optical characteristics under applied strain are scarce. Here, the engineering property of 2D AlN/BN comprising bandgap nature transition and optical absorption capability (from unstrained to strained) have been investigated using density functional theory calculations. The formation energy calculations confirm the stability of the simulated nanoheterostructure. The electronic band structure calculations demonstrate that nanoheterostructure is an indirect bandgap material with a large bandgap of 5.26 eV, which can be modified effectively by applying strain. According to the calculations, the transition from indirect to direct band gap behavior has been observed at +15% biaxial strain with 2.71 eV band gap energy. Meanwhile, calculations for optical absorption and dielectric function reveal that the system has significant absorption peaks in the ultraviolet region which are very sensitive to applied strain. As strain increases, the first absorption peaks are shifted towards a lower energy range from 5.73 eV (Ꜫ= 0 %) to 3.76 eV (Ꜫ = +15%), which features an enhancement of optical absorption for solar and solar-blind regions. Furthermore, we determined that the band edge positions in 2D AlN/BN straddled the water redox potential under strain, indicating its effectiveness as a proficient photocatalyst. These characteristics make 2D AlN/BN planer nanoheterostructure a promising candidate for applications in optoelectronics and photocatalytic water splitting performance. First principles computations based on density functional theory were employed to carry out all the calculations with a self-consistent approach. For solving the Kohn-Sham equations, the first principles dependent full-potential linearized augmented plane wave scheme were adopted. For addressing the exchange-correlation effects, the generalized gradient approximation of PBEsol functional was used. To prevent interaction between the periodic images, we have inserted a vacuum region of 10 Å in the z-direction. Non-negligible weak dispersion corrections in nanoheterostructure were considered by using the DFT-D3 method of Grimme's. The locally modified Becke-Johnson (lmBJ) exchange potential has also been applied to compute electronic and optical properties in this research to obtain more accurate information.

Ab-initio study of strain-tunable g-GaN/BN nanoheterostructure for optoelectronic and photocatalytic applications.

Two-dimensional (2D) nanoheterostructures of materials, integrating various phase or materials into a single nanosheet have stimulated large-scale research interest for designing novel two dimensional devices. In contemporary analysis present work, we examined the structural and electronic properties of the isolated 2D BN and GaN monolayers. We have investigated the structural stability and optoelectronic and photocatalytic response of the g-GaN/BN nanoheterostructure along with its response to strain. Nanoheterostructure g-GaN/BN is predicted to be a direct bandgap semiconductor with wide gap of 4.45eV, whose value can be effectively modulated by applied strain ( , ranging from 4.55 ( = - 4%) to 3.58eV ( = 8%). We also discovered that the tensile strain of 8% can substantially tune the direct bandgap of nanoheterostructure to indirect band gap nature. Even more important, the biaxial tensile strain engineering accentuates an enhancement of optical absorption in the UV region, broadening the light harvesting of the g-GaN/BN nanoheterostructure with the shifting of first absorption peak from 4.64 ( = - 4%) to 3.71eV ( = 8%). Furthermore, strain-tuned band edge potentials arrangement perfectly fits the water reduction and oxidation redox potentials. Our findings portend that the g-GaN/BN nanoheterostructure has application in prospective nanoscale optoelectronic devices and photocatalytic hydrogen evolution system. First principles calculations in this study are performed using density functional theory. Generalized gradient approximation within PBEsol functional employed to address the electron-electron exchange-correlation effects. For avoiding periodic interactions between the layers, we have inserted a vacuum region of thickness 10Å in the z-direction. For ensuring the convergence accuracy of the computed results, convergence criteria of the iteration process is set to be 0.0001eV. Local modified Becke-Johnson, a semi local functional, is applied for calculating electronic and optical properties for more accuracy of results. As in layered 2D nanoheterostructure, a factual depiction of the van der Waals interactions cannot be provided by conventional DFT techniques. Accordingly, in order to incorporate these interactions, we had employed the dispersion correction method of Grimme's.

Roles of water-soluble aerosol coatings for the enhanced radiative absorption of black carbon over south asia and the northern indian ocean

Black Carbon (BC), formed by incomplete combustion, absorbs solar radiation and heats the atmosphere. We investigated the enhancement in optical absorption of BC due to coatings of water-soluble (WS) species in the polluted South Asian atmosphere. The BC Mass Absorption Cross-section (MAC; 678 nm) was estimated before and after removal of the WS components. Wintertime samples were collected from three South Asian receptor observatories intercepting large-footprint outflow: Bangladesh Climate Observatory Bhola (BCOB; integrating outflow of the Indo-Gangetic Plain), Maldives Climate Observatories at Hanimaadhoo (MCOH) and at Gan (MCOG), both reflecting outflow from the South Asian region. The ambient MAC observed at BCOB, MCOH and MCOG were 4.2 ± 1.4, 7.9 ± 1.9 and 7.1 ± 1.5 m2 g−1, respectively.The average enhancement of the BC MAC due to WS coatings (i.e., ws-EMAC) was identical at all three sites (1.6 ± 0.5) indicating that the anthropogenic aerosols had already evolved to a fully coated morphology at BCOB and/or that subsequent aging involved two compensating evolution processes of the coating. Inspecting the key coating component sulfate; the sulfate-to-BC ratio increased threefold when transitioning from BCOB to MCOH and by about 1.5 times from BCOB to MCOG. Conversely, both WS organic carbon (WSOC)/BC and water-insoluble OC (WIOC)/BC ratios declined with distance: WSOC/BC diminished by 84 % from BCOB to MCOH and by 80 % from BCOB to MCOG, while WIOC/BC dropped by about 63 % and 59 %, respectively. Such declines in WSOC and WIOC reflect a combination of photochemical oxidation and more efficient washout of OC compared to BC. The observed changes in the SO42−/BC and WSOC/BC ratios across South Asia highlight the significant impact of aerosol composition on the optical properties of Black Carbon (BC). These findings emphasize the need for detailed studies on aerosol composition to improve climate models and develop effective strategies for reducing the impact of anthropogenic aerosols on the climate.

High-Responsivity Ultraviolet Photodetectors With Enhancement of Optical Absorption Using Graphene Components and Al2O3 Layer on Si Substrate

High-Responsivity Ultraviolet Photodetectors With Enhancement of Optical Absorption Using Graphene Components and Al₂O₃ Layer on Si Substrate

Remarkable enhancement of the nonlinear optical absorption of W18O49 by Cu doping

Advanced nonlinear optical (NLO) materials, such as metal chalcogenides, black phosphorus, and perovskites, have encountered challenges arising from their inherent low chemical and thermal stability. The desirable attributes of chemical and thermal stability are exhibited by promising metal oxides within NLO applications, whereas the NLO response of metal oxides has typically shown modest strength. In this study, we report the striking enhancement of NLO absorption in W18O49 achieved through the introduction of defects via Cu doping. Following a 4-hour doping treatment, the nonlinear absorption coefficients (βeff) of Cu-doped W18O49 exhibit remarkable values of (3.36 ± 0.11) × 103 cm GW−1 and (5.76 ± 0.33) × 103 cm GW−1 upon laser excitation at 515 and 800 nm, respectively. These values are approximately 10 and 32 times higher than those measured in the pristine samples. This performance surpasses that of various other metal oxides and stands on par with the optimal tungsten/molybdenum-based chalcogenide counterparts. Notably, our investigation reveals a direct correlation between higher levels of Cu doping and an augmented βeff. Our investigations using X-ray photoelectron spectroscopy, Raman spectroscopy, ultraviolet photoelectron spectroscopy, electron paramagnetic resonance, and density functional theory calculations reveal that Cu doping induces the creation of oxygen vacancies, precipitating a concurrent reduction in bandgap and the emergence of in-gap defect states. Transient transmittance difference spectra highlight the effective role played by in-gap defect states as excitation pathways. Consequently, a greater abundance of these in-gap states corresponds to heightened optical nonlinearity.

Enhancement of optical absorption in multiferroic 0.5PZT-0.5PFN thin films: Experiments and first-principles analysis

Multiferroic compounds have gained research attention in the field of ferroelectric photovoltaics due to the presence of transition-metal d states from magnetic ions, which tend to reduce the bandgap value. In this work, 0.5Pb(Zr0.52Ti0.48)O3–0.5Pb(Fe0.5Nb0.5)O3 [PZTFN0.5] thin films were synthesized using a sol-gel route to investigate the effect of iron doping on optical and multiferroic properties. For comparative analysis, the end-member compositions, Pb(Zr0.52Ti0.48)O3 [PZT] and Pb(Fe0.5Nb0.5)O3 [PFN], were also synthesized under identical conditions. Our results revealed that the incorporation of Fe3+ ions into the PZT lattice not only induces multiferroic behavior, but also effectively enhances the optical absorption of the material in the visible light region. Optical transitions at ∼3.0 eV (∼2.4 eV) and ∼2.7 eV (∼2.2 eV) for the direct (indirect) bandgap were determined for PZTFN0.5 and PFN, respectively, indicating that the absorption edges of the iron-containing films result more promising than PZT (direct Eg∼3.6 eV) for photovoltaic applications. Both PZTFN0.5 and PFN thin films exhibit multiferroic behavior at room temperature, with different electric and magnetic properties. While PZTFN0.5 presents saturated hysteresis loops with remanent polarization values around 10 μC/cm2 and magnetization of 1.6 emu/cm2, PFN displays significantly larger remanence (31 emu/cm2) but poorer ferroelectric properties due to the presence of leakage. Microscopic insights into the structural and electronic properties of the PZTFN0.5 solid solution were provided from first-principles calculations.

Gas Sensing Properties of Pd-Decorated GeSe Monolayer toward Formaldehyde and Benzene Molecules: A First-Principles Study.

In this study, the gas sensing properties of formaldehyde (HCHO) and benzene (C6H6) adsorbed on two-dimensional (2D) pristine GeSe and Pd-decorated GeSe (Pd-GeSe) monolayers are studied by using first-principles calculations. The adsorption energies, electronic properties, optical properties, sensitivity, and recovery time of the gas adsorption systems have been thoroughly investigated. It is found that the adsorption of C6H6 on two substrate surfaces and the adsorption of HCHO on pristine GeSe are examples of physical adsorption. However, after HCHO adsorption on the Pd-GeSe monolayer, the adsorption system exhibits an increased adsorption energy of -1.21 eV, which is more favorable compared with the other adsorption systems studied. Moreover, the electron localization function and charge transfer from Pd-GeSe to HCHO are significantly enhanced, indicating distinct chemical adsorption behavior. Furthermore, it demonstrates a larger band gap change rate of 18.8% and a significant enhancement of optical absorption upon the adsorption of HCHO on the Pd-GeSe monolayer. Additionally, the appropriate sensitivity and moderate recovery time for the adsorption of HCHO on the Pd-GeSe surface indicate that the Pd-GeSe monolayer possesses an outstanding sensing capability for HCHO gas.

Strain engineering of magneto-optical properties in C[formula omitted]B/C[formula omitted]N van der Waals heterostructure

Carbon-based bilayer van der Waals (vdW) materials are attracting much attention due to their predicted interesting physical properties. Here, we theoretically investigate electronic and optical properties of C3B/C3N vdW heterostructure (HTS) under external magnetic field and mechanical strain. The tight-binding model of the system is constructed to include the strain-induced modification of the hopping interactions. The influence of a uniform perpendicular magnetic field is included by using the Peierls substitution method. We observe the intriguing electronic and optical characteristics of the HTS under mechanical strain, covering the band inversion, alteration of band gap and optical gap, distortion of band-edge states, as well as significant enhancement of optical absorption. Furthermore, the interplay between external magnetic field and biaxial strain leads to exotic features of quantization and optical spectra. This work provides important information for the comprehension of the engineering of materials by external effects. Our study suggests that C3B/C3N vdW HTS is a promising candidate for next-generation electronic and optoelectronic devices.

Large enhancement of nonlinear optical absorption and refraction in planar chalcone structure with terminal substitution

The ultrafast nonlinear optical (NLO) properties of novel planar π-conjugated chalcone derivatives, (E)-3-(4-nitrophenyl)-1-(3-bromo-4-fluorophenyl) prop-2-en-1-one (1503) and (E)-3-(4-nitrophenyl)-1-(phenothiazin-2-yl) prop-2-en-1-one (1526) are investigated and compared. The effect of intramolecular charge transfer on NLO absorption and refraction is discussed without changing the planar structural properties of the chalcone molecules. Transient absorption experiments are used to observe the evolution of 1526 from local excited (LE) state to the intramolecular charge transfer (ICT) state. In the Z-scan experiments, 1526 exhibits respectively different nonlinear absorption (NLA) mechanisms (reverse saturable absorption and two-photon induced excited state absorption) at 532 nm (4 ns, 22ps, 190 fs) and 700–900 nm, 190 fs. The NLA and nonlinear refraction (NLR) phenomena of 1526 are observed and discussed in the POPP experiments. The experimental results indicate that the chalcone derivative can become the potential materials for laser protection.

Rational design of SiC/SnSSe heterostructure for efficient photovoltaic and photocatalytic applications

The search for highly efficient and eco-friendly photocatalysts and photovoltaic solar cells is now in progress, however, it still remains challenging. By first-principles calculations, we demonstrate that Janus SiC/SnSSe van der Waals heterostructures (vdWHs) with a typical type-II band alignment possess great potential in photocatalytic and photovoltaic applications. An intrinsic electric field induced by the Janus feature of SnSSe alongside an interfacial built-in electric field caused by charge transfer from SiC to SnSSe monolayer significantly fosters spatial separation of photogenerated electron-hole pairs in two layers. Since the reduced bandgap of the vdWHs promotes an enhancement of optical absorption in the visible and even infrared regions in comparison with that of their constituting monolayers, the solar-to-hydrogen conversion efficiency reaches as high as 41.5 %, making it a highly efficient photocatalyst. The high photoresponsivity in the visible region endows the proposed system with a powerful potential for photovoltaic applications. Besides, we also find that the optical absorption and photocurrent can be effectively tuned by applying biaxial strains. For instance, the latter increases to 31 % at 4 % tensile strain. These findings provide new prospects for designing direct Z-scheme photocatalysts and photovoltaic devices based on vdWHs.

Structural Collapse and Coating Composition Changes of Soot Particles During Long‐Range Transport

AbstractSoot particles play an important role in warming the atmosphere, but their optical absorption is highly uncertain due to their variable morphology and mixing states. Compared to short‐range transport, soot particles during long‐range transport normally undergo complicated aging processes. Here, we investigated the changes in microphysical properties and mixing states of soot particles during their long‐range transport in Eastern China. The dominant mixing state of soot particles transformed from partly coated at 60% by number to embedded status at 67% when they were transported to a downwind region 1,000 km away under cold fronts. The fractal dimension (Df) increased from 1.79 ± 0.05 for partly coated soot and 1.86 ± 0.07 for embedded soot to 1.83 ± 0.06 and 1.93 ± 0.05 following their transportation, respectively. Our study shows that aging processes of soot particles with chain‐like morphology caused their structural collapse. Moreover, we found that coating materials of aged soot particles changed from secondary inorganic‐dominated to organic‐dominated species during their long‐range transport, which suggests the aqueous formation of secondary organic aerosols on soot‐containing particles. The thick organic coating formation in some particles further induced soot redistribution from the particle center into the coating. We highlight that the Df at 1.83–1.93 is appropriate for assessing radiative absorption of long‐range transported soot particles in Eastern China and propose that soot redistribution may offset ∼13% optical absorption enhancement for long‐range transported soot particles. The microscopic changes in aged soot particles should be considered to precisely evaluate their optical absorption in the large‐scale haze layer.

Transparent conducting oxides (TCOs) based gratings for light absorption in near infrared spectrum

The present work examines the absorption enhancement of Transparent Conducting Oxides (e.g., Aluminum doped Zinc Oxide (AZO), Gallium doped Zinc Oxide (GZO), and Indium doped Tin Oxide (ITO) for widely used telecom spectral window around λ = 1550 nm. This is by virtue of the fact that the silica-based optical fiber exhibits minimum loss in this window. It is well established that one-dimensional metallic lamellar grating can significantly enhance light absorption through diffraction and excitation of surface plasmon polaritons (SPPs) at the metal-dielectric interface. This results in subwavelength confinement and hence, enhanced optical absorption in the absorbing layer near the grating. The absorption enhancement can be tuned in different spectral regions by controlling grating parameters, such as grating period, grating height, and grating aspect ratio. The present work focused on establishing Transparent Conducting Oxides (TCOs) as effective plasmonic materials for metallic grating to optimize optical absorption in the near-infrared (NIR) spectral region. The role of TCOs and the grating parameters in fine-tuning the optical absorption enhancement is investigated. Moreover, TCO grating-based designs optimized for absorption enhancement in and around the telecommunication wavelength are proposed.

Optical absorption enhancement of TiO2 via plasmonic effect of gold nanoparticles in volatile organic compounds medium

Controlling volatile organic compounds (VOC) is of utmost importance due to their adverse impacts on human health and environment. Photocatalytic degradation using TiO2 nanoparticles has emerged as a promising approach for VOC control. However, the limited photocatalytic activity of TiO2 under visible light owing to its wide bandgap presents a significant challenge. To address this limitation, the integration of plasmonic materials with TiO2 enables efficient hot electron injection into TiO2 under visible light. In this study, we investigate the influence of gold nanoparticles (AuNP) on TiO2-based structures, namely AuNP-decorated TiO2 thin films, Au@TiO2 core@shell structures, and AuNP-loaded TiO2 nanoparticles, using finite difference time domain (FDTD) simulations. Simulation results demonstrate that the presence of AuNP in TiO2 structures reduces the bandgap and enhances light absorption. Moreover, the localized electric field enhancement observed at the AuNP-TiO2 interface indicates the potential for effective hot electron injection into TiO2. Additionally, simulations conducted in a VOC medium demonstrate higher absorption compared to vacuum conditions. This work provides insights into the mechanisms underlying previously published experiments and proposes an appealing design for the development of highly efficient photocatalytic materials under visible light.

Efficiency enhancement of GaAs nanowire array-based solar cell by plasmonic Al nanoparticles

Gallium arsenide (GaAs) nanowire (NW) solar cells (SCs) have piqued the interest of researchers because they exhibit superior light-harvesting and anti-reflection properties along with reduced material consumption compared to their planar counterparts. However, the high surface-to-volume ratio associated with these NWs degrades their performance in practical applications. Light trapping is considered one of the most crucial parameters for producing low-cost high-efficiency NW-SCs. Thus, numerous light-trapping strategies have been explored, among which surface plasmon resonance (SPR) based optical absorption enhancement using metal nanoparticles (NPs) has emerged as a potential method. The role of plasmonic aluminum (Al) NPs in the efficiency enhancement of GaAs NW SC has not yet been explored. Therefore, in this study, a vertically aligned GaAs NW SC structure incorporated with Al NPs has been investigated using the finite-difference time-domain (FDTD) method. The sidewalls of GaAs NWs are embellished with uniformly arranged Al NPs with diameters ranging from 30 to 60 nm. The excitation of localized surface plasmon resonance in metal NPs results in significant light absorption enhancement at the GaAs near-band of the proposed structure. The results demonstrate that even with a low aspect ratio (D/P) of 0.3, optimizing the geometrical parameters of the NPs results in a 41.96 % increase in power conversion efficiency (PCE) and a 45 % increase in absorption efficiency at 800 nm for the proposed structure when compared to the bare structure. Hence, our suggested structure which utilizes the light-trapping mechanism of Al NPs proves to be a cost-effective and promising material combination for high-efficiency nanoscale SCs.

Enhanced photocatalytic degradation of chlorinated pesticides and polychlorinated biphenyls using Mo–TiO2/GO/MS nanocomposite

Mill scale (MS), which refers to iron waste, was used to synthesize Mo–TiO2/GO/MS nanocomposite for the photodegradation of persistent organic pollutants (POPs) via UV irradiation. By combining Mo–TiO2 as a semiconductor, graphene oxide as a supporter, and mill scale as magnetic material, we conceptually synthesized smart nanocomposite with visible light absorption and magnetic properties toward photocatalytic oxidation of POPs. Several analysis techniques such as TEM, XRD, XPS, and UV–vis were used to characterize the synthesized nanocomposite which exhibited a crystal size of 10 ± 2 nm, and optical absorption enhancement with calculated bandgap energy of 2.75eV. The photocatalytic degradation performance of 17 chlorinated pesticides was selected for testing through the synthesized nanocomposite. The photocatalytic performance using Mo–TiO2/GO/MS nanocomposite was more than 55%. The highest photocatalyst efficiency of 94.29% was achieved for the typical pesticide Endrine from water under UV illumination in less than 60 min. Additionally, polychlorinated biphenyls such as PCB 148 and PCB 15 have been effectively photocatalytic degraded with a removal efficiency of 83.42% and 67.82%, respectively. All degradation reactions of the tested persistent organic pollutants are pseudo-first-order. The enhanced photocatalytic activity was achieved by the Mo–TiO2/GO/MS catalyst relating to its good adsorption activity and efficient electron-hole charge separation.

Plasmon enhancement of third-order nonlinear optical absorption of gold nanoparticles dispersed in planar oriented nematic liquid crystals

We report structural and nonlinear optical properties of 20 nm gold (Au) nanoparticles (NPs) that are dispersed in planar degenerate (non-oriented) and planar oriented nematic liquid crystals (LCs) (4′-Pentyl-4-biphenylcarbonitrile-5CB). Taking advantage of elastic forces in the planar oriented nematic LC, we aligned AuNPs parallel to the 5CB director axis. In the case of planar degenerate, 5CB is not aligned and has no preferred orientation, forcing the AuNPs to disperse randomly. Results show that the linear optical absorption coefficient for the planar oriented 5CB/AuNPs mixture is larger than the corresponding planar degenerate sample. The nonlinear absorption coefficients are greatly enhanced in planar oriented samples at relatively high concentrations which can be attributed to plasmon coupling between the aligned AuNPs. This study demonstrates the utility of LCs for developing the assembly of NPs with enhanced optical properties which may offer important insight and technological advancement for novel applications, including photonic nanomaterials and optoelectronic devices.