Optical Properties Reflectance Research Articles

Development of hydrophilic multilayer structures for energy saving window applications using sol-gel spin coating

This study is centered on analyzing the microstructural and optical reflectivity properties of multilayers composed of dielectric titania and silica. The goal is to investigate their potential application as energy-efficient windows on glass surfaces in different modern building projects. Nevertheless, the creation of these coatings can be quite expensive due to their complex structure. This study focuses on the development of a cost-effective method to produce a multilayer structure made of titania and silica. This structure has the remarkable ability to reflect approximately 100 % of UV light and 70 % of infrared light, all achieved with just three layers. The X-ray diffraction (XRD) analysis was conducted to examine the crystallinity of the coatings. The results indicated the presence of an anatase phase, as evidenced by the Bragg angle of 25O. Empirical support was obtained through the use of Fourier transform infrared spectroscopy (FTIR), which revealed the presence of functional bonds at specific wavenumbers. Titania and silica were identified at wave numbers of 596 cm−1 and 1246 cm−1, respectively. The FTIR investigation was further supported by energy dispersive spectrum analysis (EDAX), which verified the existence of titania and silica in the multilayer structure. Through the use of field emission scanning electron microscopy (FESEM), the analysis of the multilayer structure unveiled the existence of layers composed of titania, silica, and titania. These layers were found to have thicknesses of approximately 286 nm, 315 nm, and 222 nm, respectively. The coatings were analyzed for reflectance using a UV–VIS-NIR spectrophotometer, which showed a full reflection of 100 % in the far ultraviolet range and a reflection of 70 % in the infrared region. Furthermore, the analysis of the coatings’ wetting behavior with a contact angle meter revealed their hydrophilic nature, suggesting their potential use in self-cleaning applications.

Investigation of luminescence properties and energy transfer mechanism in Sm3+ and Eu3+ co-doped BaY2ZnO5 red phosphors

In this investigation, the photoluminescence properties, energy transfer phenomenon of BaY2ZnO5:Sm3+/Eu3+ doped/co-doped phosphor are reported and synthesized by high temperature solid state reaction method. The crystal structure, micromorphology, optical diffuse reflectance and photoluminescence properties of the samples were studied. The results show that concentration quenching phenomenon is found. With the increase of Eu3+ ion concentration, the emission peaks of Sm3+ gradually decrease, indicating that energy transfer between Sm3+ and Eu3+. The optimal concentrations are 0.05 mol and 0.2 mol for single doping Sm3+ and Eu3+, respectively. The energy transfer efficiency is calculated to be 78.47–95.19 %. The BaY2ZnO5 phosphors have potential application value in the fields of white light LEDs and anti-counterfeiting.

Effect of beryllium topography on BRDF measurements

The Bidirectional Reflectance Distribution Function (BRDF) of beryllium is important for a ray-tracing simulation to evaluate the effect of reflected light on optical diagnostics in the fusion device ITER. However, the BRDF for beryllium has not been investigated yet and is currently lacking. To fill this gap, this study measured BRDFs of beryllium specimens with different topographies using goniophotometers and optimized optical reflection models. Additionally, various surface topographic parameters were computed, and their correlation with parameters for the optical reflection models was explored. As a result, it was found that topographic parameters related to slope offer a certain correlation with the parameters of the reflection model. This can be useful for determining the optical reflection properties of materials for which direct BRDF measurements are not possible.

Smaller texture improves flexibility of crystalline silicon solar cells

Flexible solar cells are widely researched for their potential usage in photovoltaics integrated into buildings, cars, unmanned arial vehicle and wearable electronics. The thin crystalline silicon solar cell (60–90 μm) is prone to crack due to surface texture when it is under bending. Here we investigated the effect of pyramid size on optical reflectivity and mechanical properties of silicon wafers. We find that smaller and uniform pyramids are beneficial for obtaining efficient and flexible silicon solar cells.

Structure, optical and magnetic properties of PVA/CuO/CoFe2O4 nanocomposite films for flexible magneto-electronic applications

Pure polyvinyl alcohol (PVA) and its nanocomposites with CuO and/or CoFe2O4 films have been prepared with different weights of ≤ 5 %. The structure of the films shows an orthorhombic phase of semi-crystalline polymer for PVA, a monoclinic phase for CuO, and a cubic phase of CoFe2O4 in nanocomposite films with particle sizes ≤ 25.5 nm, as determined by the XRD technique. Surface morphology by TEM of representative films shows the crystalline structure and nanoparticles and nanorods of individual CuO and/or CoFe2O4 compounds. The optical transmission and reflection properties of films have been measured, and the optical band gap has been estimated, showing that variable values (1.4–4 eV) can be controlled by controlling the percentage of CuO and/or CoFe2O4 in films. Magnetic investigation shows diamagnetic behavior for PVA and paramagnetic behavior for PC1, PC3, while PC5 has a very weak ferromagnetic response. Whereas nanocomposites with different contents of CoFe2O4 exhibit smooth ferromagnetic behavior with increasing Ms values. Ferromagnetic behavior has been confirmed via a convex Arrott–Belov–Kouvel plot. The improvement of magnetic properties makes the prepared films suitable to be used in various fields, such as antenna system miniaturization and flexible magneto-electronic applications.

Stability and optoelectronic properties of HfS2/HfSe2 heterostructures under tensile strain: A first-principles study

The optoelectronic properties of monolayer HfS2, HfSe2, and HfS2/HfSe2 heterostructures under biaxial strain were calculated using density functional perturbation theory (DFPT). The heterostructure formed by monolayer HfS2 and HfSe2 undergoes a transition from an indirect to a direct bandgap. Additionally, under biaxial tensile strain, the bandgaps of all systems exhibit a linear increase. The stability of the structures was further verified by calculating the phonon spectra. Monolayer HfS2 and HfSe2 exhibited imaginary frequencies at a biaxial strain of 8%, whereas the HfS2/HfSe2 heterostructure displayed an imaginary frequency at a strain of 6%. This suggests that the structures have reached their maximum load-bearing limit and lost stability. The van der Waals interactions between the layers of the heterostructure had minimal influence in the x–y plane, but they could induce interlayer tearing in the vertical direction, resulting in an earlier loss of stability compared to the monolayer structures. The optical absorption and reflectance properties of the three systems under strain were also calculated. A blue shift was observed in the low-energy region, while a significant red shift was observed in the high-energy region. The two-dimensional heterostructure exhibited significantly improved absorption coefficients and reflectance in the high-energy region compared to the two monolayer structures.

ZnO nanorods on conductive substrates. Technology and features

For obtaining ZnO nanorods (NRs) on the surface of highly conductive brass substrates, the technology of surface oxidation in argon plasma ion flows was developed that allows the formation of NRs by high-frequency helicon discharge at temperatures T ≤ 550 °C. A physical mechanism for the formation of ZnO NRs on the brass substrate is considered. The morphological, structural and physical properties of the NR samples were investigated using standard methods of research: scanning electron microscopy, energy dispersion analysis, X-ray diffraction analysis, Raman scattering, photoluminescence and optical reflectance spectra. The features of the ZnO NRs’ optical reflectance properties in terms of the location of the Restrahlen band are discussed. The quality of such nanorods is confirmed by fine details in photoluminescence and Raman shift data.

Enhancement of photoluminescence properties in Er3+-doped Gd3ScxGa5−xO12 garnet nanocrystals by Sc3+ co-doping

In this work, a series of novel garnet nanocrystals Gd3ScxGa5−xO12 (x = 0–2) doped with fixed Er3+ content were synthesized by a sol-gel combustion method. The structure, morphology, chemical composition, optical reflectance, and photoluminescence properties of the nanocrystals were investigated in detail. Following 980 nm laser excitation, steady-state and time-dependent Stokes Er3+: 4I13/2 → 4I15/2 emission spectra are investigated together with steady-state upconversion photoluminescence (UCPL) emission spectra. Although the activator content at the dodecahedral site is fixed, incorporation of Sc3+ into the octahedral site of the garnet host enhances the photoluminescence properties. The Stokes photoluminescence intensity keeps increasing with increasing Sc3+ content in the studied region. However, the intensity of UCPL is significantly increased in the Er3+-doped Gd3Sc2Ga3O12 sample. It is found that the substitution of Ga3+ by Sc3+ at the octahedral site of the studied garnet nanocrystals leads to a reduction of the maximum phonon energy and may affect the crystal field surrounding Er3+.

NIR reflective lanthanum zirconate (La2Zr2O7) ceramic colorant and its solar heat reflective glaze coatings

Pyrochlore-type rare earth ceramics are ideal for high-temperature coatings due to their exceptionally low thermal conductivity, high-temperature stability, and chemical inertness. To reduce the impact of urban heat island effect, ceramic colorants and coatings made of such materials are now required. The impact of iron oxide chromophore is investigated in this study on pyrochlore type lanthanum zirconate (La2Zr2O7) to make solar heat reflecting ceramic yellow colorant, and the same is then used for creating multifunctional glaze coatings. Using appropriate methods, the impact of iron oxide on the morphological, optical, and solar heat reflection properties of the yellow colorant is examined. The pyrochlore crystal structure and 93% NIR reflectivity of lanthanum zirconate were not impacted by the doping of iron oxide. Additionally, the glaze coating developed from the yellow colorant, surface non-wettability, NIR reflectivity, and tinting behavior were comprehensively examined and presented for the first time. The findings strongly indicated that pyrochlore La2Zr2O7 is a candidate to produce ceramic functional materials and coatings with sustained energy savings. This work opens up fresh possibilities for functional glaze coating applications using the pyrochlore type ceramic materials.

Infrared BRDF spatial scanning measurement with an optimized rotation strategy of a robotic arm

The bidirectional reflection distribution function (BRDF) reflects the optical reflection properties of opaque materials over the entire hemispherical space. Exciting measurements of infrared BRDF systems based on robotic arms are discrete in space since the incident and reflection angles were coupled deeply. In this paper, a mapping from BRDF angles to goniometer angles was developed, and the two sets of angles were decoupled using an optimized spatial rotation strategy with two scanning modes. The measurement covered the full BRDF hemispherical space. The measurement speed and resolution in the specific scanning directions were significantly improved. Meanwhile, the measurement accuracy was not reduced. An infrared BRDF measurement system using the proposed strategy was developed to measure five different samples from high to low reflectance with specular or diffuse reflection qualities. The qualities demonstrated by the calculated BRDF distributions were consistent with the infrared optical characteristics of all samples, verifying the effectiveness of the proposed system.

Optical properties and thermal degradation of NbB2/Nb(BNO)/Al2O3 spectrally selective tandem absorber

The development of any new ceramic absorber demands the evaluation of different performance-limiting properties. In a recently published paper from our research group, we reported the development of NbB2-based new tandem absorber. In our efforts to investigate further potentiality for concentrated solar power applications, this study reports the optical and angular dependent reflectance properties of the NbB2/Nb(BNO)/Al2O3 spectrally selective absorber. The optical properties (extinction coefficient and refractive index) and the dielectric constants of the coatings were determined using spectroscopic ellipsometry analysis. Such analysis together with SCOUT simulation of the reflectance spectrum, confirms the refractive index gradient from the substrate to the top layer. The angular-dependent reflectance measurement demonstrates good solar absorptance (from 8 to 48°). More importantly, the coatings exhibited good thermal stability up to 200 h in vacuum at 500 °C. Extensive transmission electron microscopy analysis reveals the traces of oxygen in the layers. The moderate decrease in absorptance can be rationalised due to the compaction and formation of an oxide layer. Based on the obtained results and earlier published studies, the potential of the NbB2-based coatings as solar selective absorber for concentrated solar power applications is established.

Investigation of reflection bands of 1D annular photonic crystal containing double negative index material and non-magnetized plasma

In this paper, optical reflectance properties of an annular photonic crystal (APC) composed of alternate layers of double negative (DNG) material and a non-magnetized plasma (NMP) layer, immersed in free space, have been theoretically investigated and studied. The reflectance spectra of the annular PC have been obtained by employing the transfer matrix method (TMM) for the cylindrical waves in the case of TEpolarized wave only. It has been found that the spectral position and width of the reflection bands of APC are greatly influenced by the variation in the thickness of DNG metamaterial and NMP layer, respectively. Interestingly, it is observed that the presence of NMP layer causes the increase in photonic band gap (PBG) whereas the DNG layer reduces the PBG. Further, the effect of azimuthal mode number (m) on the reflectance spectra shows that for m > 0, splitting in the reflection bands occurs at the frequency corresponding to the zero permeability value of DNG metamaterial layer. Moreover, with the increase in azimuthal mode number one PBG is red-shifted and the second one is blue-shifted. Finally, the effect of change in the starting radius parameter of curved surface and plasma electron density on the reflectance spectra of APC has also been studied and very interesting results have been observed.

Optimal Nb5+ doping for enhanced optical reflectivity and improved thermophysical properties of La0.9Sr0.1Ti1−xNbxO3+δ

AbstractThermal protection materials with high optical reflectivity, low thermal conductivity, and good high‐temperature stability are required for the development of laser technologies and the protection of the critical equipment components. Herein, we synthesize a novel thermal protective material, La0.9Sr0.1Ti1−xNbxO3+δ (LSTN; x = 0.1, 0.125, 0.15), with different Nb5+‐ion contents using solid‐state sintering. Phase structure analysis demonstrates that LSTN (x = 0.1, 0.125, 0.15) presents a single‐phase monoclinic structure with a uniform element distribution. In particular, the LSTN0.125 ceramic exhibits ultrahigh optical reflectivity (96%, 2300 nm) and excellent thermophysical properties, such as a high thermal expansion coefficient (10.3 × 10−6 K−1, 1000°C), an ultralow thermal conductivity (0.408 W (m K)−1, 300°C), and excellent high‐temperature stability. Aberration‐corrected scanning transmission electron microscopy reveals that the disordered substitution of Nb5+ ions induces numerous lattice distortions and mass fluctuations, which decrease the thermal conductivity, and makes difference in the relative refractive indices of atomic layers causing the high reflectivity of the material. These remarkable properties render the LSTN0.125 ceramic as an ideal alternative for near‐infrared thermal protection applications.

Tunable Reflection Properties and Photonic Bandgap Behavior of a One-Dimensional Metamaterial-Superconductor-Based Ternary Photonic Crystal

In the present communication, we have investigated the tunable reflection properties and photonic bandgap variation of a one-dimensional metamaterial and superconductor based ternary photonic crystal. To design the 1D ternary photonic crystal, we have taken three alternate layers of metamaterial, superconductor (BSSCO), and silica (SiO2). Transfer matrix method (TMM) is employed to determine the optical reflection properties of the considered 1DPC for TE-mode by varying five parameters, viz. incident angle, superconductor temperature, thickness and refractive index of dielectric layer, and number of unit cells. It is noted that the ternary PC exhibits the features of tunable narrow band reflector, whose width increases with increase in the incident angle with a blue shift, and decreases with operating temperature of superconductor with red shift. It also enhances with increase in the dielectric layer thickness in low frequency region, and decreases in high frequency regime with red shifts. We obtain only one PBG at n3=1.46 in low frequency regime, while with increase in the refractive index multiple gaps are obtained in different frequency regions having distinct widths at n3=2.4 and 3.4. An increase in the number of unit cells causes increase in the reflectance, wherein no PBG is found below N=8. This analysis gives some insights to design tunable devices based on narrowband reflectivity in the terahertz frequency regime, including THz-metadevices, emitters, thermo-optical devices, and security sensors.

Characterization of anti-reflection structures fabricated via laser micro/nano-processing

The optical reflection properties of material surfaces are crucial for the performance of many optical and optoelectronic devices. In this study, different single-scale surface structures, e.g., gratings, holes, and cones were fabricated via laser micro/nano-processing and their optical properties were determined. The anti-reflection mechanism for these surface structures was revealed visually by using a ray-tracing algorithm and wave optics calculations. To fully exploit the advantages of single-scale nanostructures or microstructures, a novel preparation method for multi/scale structures was proposed. It not only improves absorption efficiency, but also broadens the absorption spectrum. Moreover, a substantial improvement of the infrared anti-reflection performance was realized. In addition, the relationship between the characteristic of surface structure and the spectral region in response to incident light, was established.

The Spectroscopic and Antimicrobial Yield of Sol-Gel Derived Zinc Copper Silicate/E102 Nanoclusters

The structural and optical properties of 30 ZnO: 50 SiO2: (20-x) CuO (ZSC) loaded with E102 (tartrazine dye) (where x = 0.02, 0.05, 0.07 wt.%) nanoclusters have been explored. These nanoclusters were synthesized by a sol-gel route followed by a very controlled crystallization process at 500 °C. The phase formation, structural modification, and particle distribution behavior of these nanoclusters have been studied using XRD and TEM analysis to monitor the domestic environment for ZCS-E102. The optical transmission and reflection properties of nanoclusters in the UV–Vis-NIR range were studied for the present nanoclusters from which the optical absorption was calculated. Tauc method is employed to estimate the type and value of energy needed to gap transition from absorption data. The direct and indirect gap shows decreased energy need for its transition by E102 concentration increase. The antimicrobial potentials of four synthesized nanoclusters were performed against some pathogenic microbes. The toxicity performance of all studied nanoclusters is measured. Results revealed that ZSC-0.07E102 is showed an effective antimicrobial action against four tested pathogenic microbes in terms of excellent inhibitory effect and biocompatibility show noticeable potential in the antimicrobial application. Therefore, this proficient nanomaterial is a promising choice for biomedical purposes.

Optical properties of two-dimensional materials with tilted anisotropic Dirac cones: theoretical modeling with application to doped 8-Pmmn borophene

The optical reflection, transmission and absorption properties of borophene, a newly discovered two-dimensional material with tilted anisotropic Dirac cones, are explored within a simple electronic band structure model of 8-Pmmn borophene, proposed by Zabolotskiy and Lozovik (2016 Phys. Rev. B 94 165403). It is assumed that the borophene layer is deposited on a dielectric substrate, such as Al2O3, and that the borophene’s electron density is controlled by an external gate voltage. The reflectance, transmittance and absorbance of the borophene layer, the conduction band of which is filled with electrons up to the Fermi level, are calculated against the frequency of the incident radiation, as well as on the angle of its incidence on the layer. Considered are the two principal cases of the incident radiation polarization either parallel to or normal to the plane of incidence. We reveal that the optical characteristics of 8-Pmmn borophene are distinctly different for the above two cases at all angles of radiation incidence, excepting the grazing incidence, for which the borophene layer is found to behave like a mirror regardless of the wave polarization. The results obtained indicate the possibility of visualizing the borophene layer deposited on a dielectric substrate by observing the minimum reflectivity of this layer at a certain angle incidence (called the quasi-Brewster angle) of the p-polarized radiation, which may differ by a value of about ten degrees from the Brewster angle of the substrate.

Optical Material Characterisation of Prepreg CFRP for Improved Composite Inspection

Automated fibre layup techniques are often applied for the production of complex structural components. In order to ensure a sufficient component quality, a subsequent visual inspection is necessary, especially in the aerospace industry. The use of automated optical inspection systems can reduce the inspection effort by up to 50 %. Laser line scan sensors, which capture the topology of the surface, are particularly advantageous for this purpose. These sensors project a laser beam at an angle onto the surface and detect its position via a camera. The optical properties of the observed surface potentially have a great influence on the quality of the recorded data. This is especially relevant for dark or highly scattering materials such as Carbon Fiber Reinforced Plastics (CFRP). For this reason, in this study we investigate the optical reflection and transmission properties of the commonly used Hexel HexPly 8552 IM7 prepreg CFRP in detail. Therefore, we utilise a Gonioreflectometer to investigate such optical characteristics of the material with respect to different fibre orientations, illumination directions and detection angles. In this way, specific scattering information of the material in the hemispherical space are recorded. The major novelty of this research are the findings about the scattering behaviour of the fibre composite material which can be used as a more precise input for the methods of image data quality assessment from our previous research and thus is particularly valuable for developers and users of camera based inspection systems for CFRP components.

Infiltration of Proteins in Cholesteric Cellulose Structures.

Cellulose nanocrystals (CNCs) can spontaneously self-assemble into chiral nematic (cn) structures, similar to natural cholesteric organizations. The latter display highly dissipative fracture propagation mechanisms given their “brick” (particles) and “mortar” (soft matrix) architecture. Unfortunately, CNCs in liquid media have strong supramolecular interactions with most macromolecules, leading to aggregated suspensions. Herein, we describe a method to prepare nanocomposite materials from chiral nematic CNCs (cn-CNCs) with strongly interacting secondary components. Films of cn-CNCs were infiltrated at various loadings with strongly interacting silk proteins and bovine serum albumin. For comparison and to determine the molecular weight range of macromolecules that can infiltrate cn-CNC films, they were also infiltrated with a range of poly(ethylene glycol) polymers that do not interact strongly with CNCs. The extent and impact of infiltration were evaluated by studying the optical reflection properties of the resulting hybrid materials (UV–vis spectroscopy), while fracture dissipation mechanisms were observed via electron microscopy. We propose that infiltration of cn-CNCs enables the introduction of virtually any secondary phase for nanocomposite formation that is otherwise not possible using simple mixing or other conventional approaches.

Comparison of omnidirectional reflectivity of quasi-periodic dielectric multilayers

Optical reflectivity properties of various dielectric multilayer sequences of thin films are investigated. Wavelength, incident angle, TE, TM polarization parameters are changed and omnidirectional polarization and wavelength independent highly reflective structures are researched. In this research 1D periodic, Fibonacci, Thue–Morse, double-period and Rudin–Shapiro sequences are considered. It is found that the perfect reflective structure can be obtained with single period Rudin–Shapiro structure with a high order.