Related Optical Properties Research Articles

Optical characterization of hafnium boride and hafnium carbide-based ceramics for solar energy receivers

The availability of spectrally-selective, thermally stable and more efficient sunlight absorbers represents a crucial aspect for the development of solar energy technologies able to operate at elevated temperature. In this regard, the optical properties of dense HfB2, HfC, HfB2-SiC and HfB2-HfC-SiC products are assessed, compared and discussed in the present work, in view of the possible utilization of such Ultra-High-Temperature Ceramics (UHTCs) for thermodynamic solar energy conversion. The materials above are first produced in bulk form by Spark Plasma Sintering (SPS), starting from ceramic powders preliminarily prepared by Self-propagating High-temperature Synthesis (SHS), or by reactive-SPS, using elemental reactants. All sintered specimens displayed relative density above 95%, with the composite systems approaching the theoretical density values, due to the beneficial role played by SiC as sintering aid, which also improves the oxidation resistance of the resulting UHTCs. The material composition is found to largely affect the related optical properties, as the SiC addition typically increases solar absorbance and decreases spectral selectivity with respect to pure UHTC boride and carbide phases. A final discussion is given about the best tradeoff material.

Synthesis of bornite Cu5FeS4 nanoparticles via high energy ball milling: Photocatalytic and thermoelectric properties

Cu5FeS4 bornite nanoparticles with sizes in the range from 10 nm to 40 nm were synthesized by high energy mechanical alloying (MA) and annealing. The phase evolution during MA and the related optical properties were studied. X-ray diffraction analysis showed the crystal structure of synthesized powders to adopt the high bornite phase after 2 h of MA. Following an annealing treatment at 300 °C for 20 min, the nanoparticle crystal structure changed to low bornite. The band gap of bornite nanoparticles was estimated to be about 0.87 eV for low bornite and 1.23 eV for high bornite. The photoresponse of low bornite nanoparticles indicated a transient photocurrent with fast recombination of photo-induced electron-hole pairs. The thermal conductivity of consolidated nano-powder was 0.46 W m−1 K−1 at room temperature and remained very low over the measured temperature range of 30–320 °C. A peak ZT value of 0.28 was obtained at 320 °C for consolidated nano-powder. As low bornite is stable at room temperature, the results suggest the possible use of this material, made of inexpensive and earth abundant elements, for energy conversion through thermoelectrics or photocatalysis.

Study of the structural, elastic, electronic and optical properties of lead free halide double perovskites Cs2AgBiX6(X = Br, Cl)

The lead free halides double perovskites show a particular interest in the conception of perovskites solar cells. We predicted the lattice constant and the atomic Wycko position of these lead free halide double perovskites Cs2AgBiX6 (X = Br, Cl) under pressure effect. The alloying ability of crystal, elastic constants and related parameters, electronic and optical properties have been studied using pseudo potential plane wave method based on the density functional theory. The investigated lead free halide double perovskites Cs2AgBiX6 (X = Br, Cl) show a weaker resistance to compression along the a-axis. This result also proves the existence of a directional bonding between atoms and a weaker resistance to compression along the a-axis The band structure indicates that Cs2AgBiX(X = Br, Cl) are X–L indirect gap semiconductors. Our computed bulk modulus and its pressure derivative of double perovskites Cs2AgBiX6 (X = Br, Cl) are predictions. The calculated elastic constants of Cs2AgBiX6 (X = Br, Cl) at equilibrium and under pressure effect are predictions.

Physical and optical investigation of lutetium-sodium-borate glasses

Physical and optical properties of lutetium sodium borate glasses have been examined. A series of glass samples with the different chemical composition xLu2O3:20Na2O:(80-x)B2O3 (where x = 5, 10, 15 and 20 mol%) were successfully fabricated by a melt quenching technique and their properties were investigated through various techniques include density, absorption, and X-ray diffraction. The amorphous nature was confirmed by the presence of a broad hump in the XRD pattern. The relevance parameters related physical and optical properties have been calculated and discussed.

Enhanced and one-way absorptance of LiNiO2 thin films in one-dimensional photonic crystals

The refractive index of LiNiO2 thin films is complex and exhibits both dielectric and metallic properties. With LiNiO2 thin films coated on or inserted in photonic crystals (PCs), it is possible to enhance the absorptance in the designed (AB)nLiNiO2(BA)m PC structures. One-way absorption in the photonic bandgap of (AB) PCs has been observed via changing the optical transmitting direction. The positions, width, and strength of the absorption peaks depend on the thickness of the LiNiO2 films, the incident angles, and the transverse electric/transverse magnetic modes. The photonic band structure can be employed to determine the allowed and forbidden photonic modes and the related optical properties for (AB) PC and (AB)nLiNiO2 PCs. These novel absorption characteristics can enrich the optoelectric properties of LiNiO2 thin films.

TEM characterization and cathodoluminescence study of mixed-phase ZnS nanostructures

In this work, we reported the synthesis of ZnS nanostructures featured a laminated morphology through a feasible chemical vapor deposition process. The microstructure and phase purity of as-synthesized ZnS nanostructures were examined by using an X-ray diffractometer (XRD) and high-resolution transmission electron microscope (TEM), and it was found that mixed cubic and hexagonal ZnS phases co-existed. The formation of cubic and hexagonal ZnS phases was derived from the numerous stacking faults generated inside the laminated ZnS nanostructures. Optical characterization of the ZnS nanostructures using cathodoluminescence spectrometer indicated that a broad emission band covering the wavelength of 400–600 nm in the visible range has been observed. Finally, the formation mechanism and related optical property of ZnS nanostructure were discussed based on TEM and CL results.

Universal features of the optical properties of ultrathin plasmonic films

We study theoretically confinement related effects in the optical response of thin plasmonic films of controlled variable thickness. While being constant for relatively thick films, the plasma frequency is shown to acquire spatial dispersion typical of two-dimensional materials such as graphene, gradually shifting to the red with the film thickness reduction. The dissipative loss, while decreasing at any fixed frequency, gradually goes up at the plasma frequency as it shifts to the red with the film thickness reduced. These features offer a controllable way to tune spatial dispersion and related optical properties of plasmonic films and metasurfaces on demand, by precisely controlling their thickness, material composition, and by choosing deposition substrates and coating layers appropriately.

Effect of Surface Passivation on CdxNi1-xS Thin Films Embedded with Nickel Nanoparticles

Certain treatments done to binary CdS , such as incorporating Ni onto CdS produces ternary thin films may cause major optical parameters that have a number of applications including for solar cell device fabrication. In this paper, we report on the effect of surface passivation on the band gap and other related optical properties of CdNiS thin films. Thin films for Cd x Ni 1-x S were prepared on glass substrates by chemical solution method. Effects of surface passivation and variation of the volume of nickel ions on the optical properties CdS hence obtaining Cd x Ni 1-x S thin films was investigated. It was observed that the thin films hard an average Transmittance above 68 %, with reflectance below 25 % across UV-VIS-NIR region. A plot of ( αhν ) 2 versus hν gave energy band gap between 2.55–3.49 eV for as-grown samples and 2.82–3.50 eV for annealed samples. The passivated samples had band gap energy values within the range 2.85–3.12 eV. It was concluded that an increase in concentration of Cd 2+ and Ni 2+ ions in the reaction led to an increase the band gap while optical conductivity ranged between 3.78x10 11 –2.40x10 12 S -1 .

First-principles study of (Ga, Al)-codoped ZnO for optoelectronic device application

The relative stability, electronic structure, and optical properties of (Ga–Al)-codoped ZnO were investigated by first-principles calculations based on density functional theory (DFT). To study the doping effects, ZnO supercells with 32 atoms were built. The results were obtained by using Material Studios 8.0 provided by Accelrys. Ab initio spin-polarized all-electron DFT computations have been performed for substitution. The results indicate that the energy band shifts towards the higher-energy region for Al- and/or Ga-doped ZnO, which endorsed the doping of Al and/or Ga. It has been observed that the preparation of (Ga–Al)-codoped ZnO is difficult compared to Al/Ga-doped ZnO due to the considerably larger formation energy required. The imaginary part of the dielectric function ε2(ω), reflectivity R(ω), absorption coefficient α(ω), and refractive index n(ω) were calculated. The contribution of different density of states in the formation of the conduction and valence band has been analyzed for different configurations of ZnO.

First results from light scattering enhancement factor over central Indian Himalayas during GVAX campaign

The present work examines the influence of relative humidity (RH), physical and optical aerosol properties on the light-scattering enhancement factor [f(RH=85%)] over central Indian Himalayas during the Ganges Valley Aerosol Experiment (GVAX). The aerosol hygroscopic properties were measured by means of DoE/ARM (US Department of Energy, Atmospheric Radiation Measurement) mobile facility focusing on periods with the regular instrumental operation (November–December 2011). The measured optical properties include aerosol light-scattering (σsp) and absorption (σap) coefficients and the intensive parameters i.e., single scattering albedo (SSA), scattering Ångström exponent (SAE), absorption Ångström exponent (AAE) and light scattering enhancement factor (f(RH)=σsp(RH, λ)/σsp(RHdry, λ)). The measurements were separated for sub-micron (<1μm, D1μm) and particles with diameter<10μm (D10μm) in order to examine the influence of particle size on f(RH) and enhancement rate (γ). The particle size affects the aerosol hygroscopicity since mean f(RH=85%) of 1.27±0.12 and 1.32±0.14 are found for D10μm and D1μm, respectively. These f(RH) values are relatively low suggesting the enhanced presence of soot and carbonaceous particles from biomass burning activities, which is verified via backward air-mass trajectories. Similarly, the light-scattering enhancement rates are ~0.20 and 0.17 for the D1μm and D10μm particles, respectively. However, a general tendency for increasing f(RH) and γ is shown for higher σsp and σap values indicating the presence of rather aged smoke plumes, coated with industrial aerosols over northern India, with mean SSA, SAE and AAE values of 0.92, 1.00 and 1.15 respectively. On the other hand, a moderate-to-small dependence of f(RH) and γ on SAE, AAE, and SSA was observed for both particle sizes. Furthermore, f(RH) exhibits an increasing tendency with the number of cloud condensation nuclei (NCCN) indicating larger particle hygroscopicity but without significant dependence on the activation ratio.

Time‐Resolved Plasmonics used to On‐Line Monitor Metal/Elastomer Deposition for Low‐Voltage Dielectric Elastomer Transducers

Compliant hetero‐nanostructures provide access to nano‐photonics, flexible electronics, and artificial muscles. These nanometer‐thin polymers and metals are regularly predicated on molecular beam deposition—a technique that leads reliably to homogeneous films and enables the precise in situ monitoring of forming nanostructures. Herein, it is demonstrated that spectroscopic ellipsometry can be used to on‐line monitor film formation with a sub‐nanometer resolution and the evolution of the related optical properties of the hetero‐nanostructure. The data recorded include plasmonic fingerprints of Au islands as well as film formation on self‐assembled polydimethylsiloxane (PDMS). Bi‐functionalized thiol‐PDMS, tailored for thermal deposition, serves as a self‐assembled adhesion layer for Au electrodes. Suppressed localized plasmonic activity indicates the formation of a homogeneous Au film on thiol‐PDMS and wrinkled Cr/PDMS, contrary to the well‐known establishment of Au islands on bare PDMS. The tailored hetero‐nanostructures based on Au/thiol‐PDMS and Au on wrinkled Cr/PDMS adhesion layers enable the fabrication of stretchable electronics and low‐voltage dielectric elastomer sensors and actuators for artificial muscles and tunable optics.

The Lattice Structure and Optical Properties of Neodymium-Doped Gadolinium Vanadate Crystals Induced by Ion Irradiation

In recent times, the neodymium-doped gadolinium vanadate (Nd:GdVO4) crystal has attracted significant attention as one of the most valuable functional materials, but its lattice structure can be easily modified in an irradiation environment, which determines its related optical properties and affects the performance of devices based on the Nd:GdVO4 crystal. The near-surface lattice structure change and damage are studied through the displacement per atom (dpa), X-Ray diffraction, hardness and elastic (Young's) modulus, and micro-Raman spectroscopy techniques. We discover that the intensity and peak position of micro-Raman have obvious changes between waveguide and substrate region in Nd:GdVO4 crystal. The related optical properties induced by the structural changes, including the absorption bands and refractive index profiles, are investigated. A new absorption peak was observed after irradiation of the Nd:GdVO4 crystals by C3+ ions. Thus, waveguide optical-coupling techniques identified that the ion- irradiated Nd:GdVO4 crystal can support single-mode or multimode propagation at 633 nm. The fabricated waveguide structures emerge as promising candidate for photonic design and integrated optical devices, which will have a huge application prospect in multimedia and internet.

Effects of annealing temperature and duration on the morphological and optical evolution of self-assembled Pt nanostructures on c-plane sapphire.

Metallic nanostructures (NSs) have been widely adapted in various applications and their physical, chemical, optical and catalytic properties are strongly dependent on their surface morphologies. In this work, the morphological and optical evolution of self-assembled Pt nanostructures on c-plane sapphire (0001) is demonstrated by the control of annealing temperature and dwelling duration with the distinct thickness of Pt films. The formation of Pt NSs is led by the surface diffusion, agglomeration and surface and interface energy minimization of Pt thin films, which relies on the growth parameters such as system temperature, film thickness and annealing duration. The Pt layer of 10 nm shows the formation of overlaying NPs below 650°C and isolated Pt nanoparticles above 700°C based on the enhanced surface diffusion and Volmer-Weber growth model whereas larger wiggly nanostructures are formed with 20 nm thick Pt layers based on the coalescence growth model. The morphologies of Pt nanostructures demonstrate a sharp distinction depending on the growth parameters applied. By the control of dwelling duration, the gradual transition from dense Pt nanoparticles to networks-like and large clusters is observed as correlated to the Rayleigh instability and Ostwald ripening. The various Pt NSs show a significant distinction in the reflectance spectra depending on the morphology evolution: i.e. the enhancement in UV-visible and NIR regions and the related optical properties are discussed in conjunction with the Pt NSs morphology and the surface coverage.

Effects of internal relaxation under inplane strain on the structural, electronic and optical properties of perovskite BaZrO3

We present the specific ab-initio calculations that detail the variations of perovskite BaZrO3 caused by in-plane strain. Specifically, the internal relaxation, which was not captured in the widely used biaxial strain model, was included in a complementary manner to lattice relaxation. Density functional theory as well as a hybrid functional method based on a plane wave basis set was employed to calculate the lattice structure, elastic constants, electronic properties and optical properties of perovskite BaZrO3. The lattice parameter c exhibited a clear linear dependence on the imposed in-plane strain, but the Poisson’s ratio caused by internal relaxation was smaller than the elastic deformation, indicating an “inelastic” or “plastic” relaxation manner caused by the introduction of internal relaxation. As a result, the related electronic and optical properties of perovskite BaZrO3 were also strongly affected by the in-plane strain, which revealed an effective way to adjust the properties of perovskite BaZrO3 via internal relaxation.

The off-stoichiometry effect on the optical properties of water-soluble copper indium zinc sulfide quantum dots

CuInZnS quantum dots (CIZS QDs) were prepared via reflux method in aqueous solution using CuCl2·2H2O, InCl3·4H2O, Zn(OAc)2·2H2O and Na2S·9H2O as raw materials, l-glutathione (GSH) and sodiumcitrate (SC) as stabilizing agents, respectively. The effects of off-stoichiometry (Cu/In and Zn/Cu ratios) on the crystal structure and morphology were systematically studied by means of X-ray diffraction (XRD) and high-resolution transmission electron microscope (HRTEM), and the relative optical properties were also investigated by absorption and fluorescence spectra. The as-prepared water-dispersible CIZS QDs were around 3–4nm and possessed the tetragonal chalcopyrite crystal structure. The photoluminescence (PL) intensity of QDs was significantly increased with decreasing the Cu/In ratio. Compared with the Cu/In ratio variation, changing Zn/Cu ratio was an effective strategy to realize a more uniform irradiation and a wide range of emission wavelength tunability.

Tuning the band gap and optical spectra of monolayer penta-graphene under in-plane biaxial strains

Using first principles calculations, structural, electronic and optical properties of monolayer penta-graphene (MPG) have been studied under different types of in-plane biaxial strains at different magnitudes. The results exhibit that MPG structure under small magnitude of biaxial compressive and tensile strains are more stable than those with large magnitude of strains. It is found that free- strained MPG is an indirect band-gap semiconductor with a band gap of 2.22eV using PBE functional, approximately equal to those of GaN and ZnO. Appling tensil strain slightly increases the bang gap of MPG, while exerting compresive tensile reduces it. The linear photon energy-dependent dielectric functions and related optical properties including refraction index, real part of conductivity and electron energy-loss spectrum (EELS) were also computed and discussed. The optical calculations illustrate that applying tensile and compressive strains on MPG result in blue and red shift in optical spectra. The results obtained from our calculations are beneficial to practical applications of these strained MPG structures in optoelectronics and electronics.

Temperature-dependent photoluminescence properties of mixed-cation methylammonium–formamidium lead iodide [HC(NH2)2]x[CH3NH3]1−xPbI3 perovskite nanostructures

Orthorhombic–tetragonal phase transition, temperature-dependent PL related optical properties and Urbach tail characteristics are systematically investigated in the FAxMA1−xPbI3 nanostructures.

Layer-number dependent and structural defect related optical properties of InSe

We present systematic investigations on the layer-dependent optical properties of InSe and modify its excitonic states by electron beam irradiation.

Optical and hygroscopic properties of Asian dust particles based on a horizontal Mie lidar: case study at Hefei, China

As an extension of the Mie lidar technique to measure the extinction coefficient of the surface particles, a horizontally pointing Mie lidar is used for determining the optical properties of Asian dust, which is an approach without knowing the actual lidar ratio. A long lasting dust event is observed based on this approach in May 2014. The “no dust,” “pure dust,” and “polluted dust” stage is observed during this event, and their optical and hygroscopic properties are discussed. Some new optical and hygroscopic features are observed, which benefit from the quantitative, multi-wavelength, and continuous measurement of the extinction related optical properties of dust particles.

Damage evolution and waveguide formation in SrTiO3 crystal irradiated by tens of MeV Si ions

In this work, lattice damage behavior and optical waveguide formation in SrTiO3 crystal induced by swift ion irradiation have been studied. SrTiO3 crystal with (100) surface normal zone axis direction has been irradiated by 20MeV Si3+ ions with a fluence of 1×1015cm−2 at 300K. Subsequently, structural damage induced by nuclear or electronic energy loss processes along ion penetration path has been analyzed by complementary characterization techniques, and the results indicate that the produced lattice damage in this case should be attributed to the nuclear energy loss. Utilizing the change of refractive index in lattice damage region, waveguide structure has been successfully prepared and the related optical properties have been studied through various coupling techniques. The iWKB (inverse Wentzel-Kramers-Brillouin)-reconstructed refractive-index profile of irradiation region appears reasonable correspondence (symmetrical inversion) with SRIM-simulated dpa profile, which also proves that lattice damage and waveguide formation in SrTiO3 should be ascribed to the nuclear energy loss during tens of MeV Si-ion irradiation process.