Absorption Extinction Research Articles

Quantification of the Optical Properties of Perovskite Nanocrystals Using a Combination of Polarized Resonance Synchronous and Polarized Anti-Stokes, On-Resonance, and Stokes-Shifted Spectroscopy

Reliable quantification of the optical properties of perovskite nanocrystals (PNCs) is necessary for rational PNC design and applications in optoelectronics. Presented herein is the experimental evaluation of the photon scattering, absorption, and on-resonance fluorescence (ORF) cross sections of lead halide PNCs. Four CsPbX3 (X = Cl, Br, or I) PNCs fabricated through anion exchanges with the same parent PNC CsPbCl3 were studied using UV–vis, fluorescence, polarized resonance synchronous spectroscopic (PRS2), and the polarized anti-Stokes-shifted, on-resonance, and Stokes-shifted (PAOS) spectroscopic methods. All of the PNCs exhibit strong ORF in the wavelength region where the PNC absorption and fluorescence spectra overlap. The PNC optical properties under resonance excitation and detection conditions differ in different wavelength regions. They are simultaneous light absorbers and scatterers in the wavelength region shorter than the blue-edge wavelength of the PNC ORF peak; simultaneously, photon absorbers, scatterers, and emitters in the wavelength region where the PNC is ORF active; and light scatterers alone in the wavelength region longer than the red-edge wavelength of the PNC ORF peak. The PNC peak ORF wavelength and absorption extinction cross section increase with increasing fraction of heavy halides. However, the ORF cross section and quantum yield (QY) of the iodide-containing PNCs are several folds lower than those of their counterpart iodide-free PNCs. The effects of sample aging on the PNC optical properties have been quantified in terms of PNC absorption, scattering, and ORF cross sections and ORF QY. In addition to providing a series of quantitative information not accessible before, we anticipate that the devised methodology will be extended to fluorescent nanomaterials for which the existing tools are inadequate for decoupling the complex interplay among light UV–vis absorption, scattering, and fluorescence emission that can concurrently occur under the same excitation and detection conditions.

Numerical and experimental studies of extinguishment of cup-burner flames by C6F12O

The extinguishment of propane cup-burner flames by a halon-replacement fire-extinguishing agent C6F12O (Novec 1230) added to coflowing air in normal gravity has been studied computationally and experimentally. The time-dependent, axisymmetric numerical code with a detailed reaction mechanism (up to 141 species and 2206 reactions), molecular diffusive transport, and a radiation model, is used to reveal a unique two-zone flame structure. The peak reactivity spot (i.e., reaction kernel) at the flame base stabilizes a trailing diffusion flame, which is inclined inwardly by a buoyancy-induced entrainment flow. As the volume fraction of the agent in the coflow is increased gradually, the total heat release increases up to three times due to unwanted combustion enhancement by exothermic reactions to form HF and CF2O in the two-zone trailing flame; whereas at the base, the flame-anchoring reaction kernel weakens (the local heat release rate decreases) and eventually the flame blows off. A numerical experiment, in which the C6F12O agent decomposition reactions are turned off, indicates that for addition of inert C6F12O, the maximum flame temperature decreases rapidly due to its large molar heat capacity, and the blow-off extinguishment occurs at ≈1700 K, a value identical to that for inert gases previously studied, while the reaction kernel is still burning vigorously. The calculated minimum extinguishing concentration of C6F12O in a propane flame is 4.12 % (with full chemistry), which nearly coincides with the measured value of 4.17 ± 0.30 %.

Insight into the optical properties of poly-methyl-methacrylate (PMMA) loaded with ferric chloride (FeCl3) in varying concentration

The present work has been carried out to understand the variations in a physical property that occur on insertion of a filler material in a polymer. Here, the authors report the synthesis and optical characterization of thin films of FeCl3 doped poly (methyl methacrylate) (PMMA). These films have been prepared by dispersing FeCl3 in different concentration (1%,2%,4%,8%) in PMMA using the solution casting technique. The thickness of the developed films is 100 μm. The optical properties of pure PMMA film and PMMA films doped with FeCl3 were investigated by recording the transmittance data on EI 2375 UV–VIS double beam spectrophotometer in the wavelength range 400–1100 nm. Results show that transmittance of the films decreases as the concentration of metal salt increases, attaining a minimum transmittance of 59% for 8 wt% of filler. This transmission data is further used to evaluate all other optical parameters like absorption coefficient (α), extinction coefficient (κ), refractive index (η), real and imaginary parts of dielectric constant (εr andεi), optical conductivity (σ) and skin depth (χ). The optical energy band gaps (Eg) have also been calculated.

Light absorption and light extinction in barley (Hordeum vulgare L.) as affected by planting dates and plant genotypes

Plant light absorption and extinction may affect plant growth and yield. A split plot experiment (with three replications) was carried out in the Research Field of Agricultural College, Islamic Azad University, Isfahan, Iran, during 2011–2012 in order to determine the influence of light absorption and extinction on barley growth and yield. Planting dates including Oct 10th (P1), 25th (P2), and Nov 10th (P3) and plant genotypes including Nosrat (N), 4Shur (S), and Fajr 30 (F) were used as the main- and sub-plots, respectively. Plant growth and yield as well as crop light absorption and extinction were determined at different growth stages. Using a light meter, the rate of photosynthetically active radiation of canopy in the range of 400–700 nm was determined (41–57%). Light extinction coefficients (0.355–0.485) were also determined according to the Beer-Lambert law. Planting dates and genotypes significantly affected crop growth, yield, and response to light. S resulted in the highest rate of light extinction and absorption at P1 and P3, respectively, and it also resulted in the highest rate of grain yield (4228 kg ha−1) and harvest index (40.9). These results indicated the positive correlation between the growth and yield of barley genotypes with light absorption and extinction. Such findings can be used for a more efficient designing of a barley canopy with higher growth and yield.

Arsenic modified (Ge11.5Te12.5Se67.5)100-x compound for IR application

Multi-component selenium rich glasses with various arsenic content have been prepared using conventional melt-quenching technique. XRD, SEM and EDX were carried out to study the structure of the prepared samples. From XRD it is found that studied samples are amorphous. DSC has been recorded which confirms that the prepared material is of glassy nature. FTIR spectra give information regarding presence of impurities in the glass. Optical parameters like α, Eg, Eu and n have been determined from the UV–Vis transmittance spectra. It has been noticed that the film transparency and optical bandgap have been increased whereas the absorption coefficient and extinction coefficient k decreased with increasing As concentration. It was found that the prepared samples obey the allowed indirect transition process. The increase in optical bandgap with As concentration has been described by Mott and Davis model. The refractive index shows ordinary dispersion behavior while it increases with As concentration.

A compound silica-trifluoroacetyl powder for fire suppressant: Preparation, characterization and suppression mechanism discussion

This paper reported the preparation, fire suppression efficiency, and suppression mechanism of a new suppression powder. In present work, the new suppressant was designed for combining the ability of terminating the chain reactions into the powder extinguishing agent. The trifluoroacetyl group (COCF3) was grafted onto the silicon dioxide (SiO2), and called the compound SiO2–F. Several tests for characterizing the structure and morphology of the compound powder were done. The results indicated that the powder was prepared successfully. Then, the burning velocity of methane-air flame with powder addition and minimum extinguishing concentration were measured to evaluate the fire suppression efficiency. In comparison with NaHCO3 and SiO2 powders, the SiO2–F powder had more pronounced fire suppression efficiency. Furthermore, the fire suppression mechanism of the powder was systematically studied. The physical and chemical suppression mechanisms worked together to suppress the flame. The physical suppression mainly stemmed from the heat absorption of solid substances, and occupied 23.1% of the total suppression effect. The chemical suppression was mainly due to the termination of chain reactions by the fluorinated species which were released when the powder was exposed to high temperature.

Synthesis and characterization of multi-substituted carbazole derivatives exhibiting aggregation-induced emission for OLED applications

A series of carbazole based derivatives differing in the number of dicyanovinyl acceptors and donors ( N -alkyl carbazole or N -phenyl carbazole) are designed, synthesized and characterized. The effect of donors on optical, electrochemical and thermal properties of carbazole-dicyanovinyl dyads is critically analysed. The dyes containing C3-linked carbazole donor showed red-shifted absorption and larger molar extinction coefficients when compared to the dyes those containing N -phenylcarbazole attributable to the extended conjugation of C3-linked N -butylcarbazole. All the compounds showed positive solvatochromism in fluorescence attributable to intramolecular charge transfer in excited state. The higher thermal stability of the dyes suggests the rigidity of the carbazole derivatives. Interestingly, all the dyes containing N -phenylcarbazole showed aggregation-induced emission properties in THF-H 2 O mixtures attributable to increased distortion in molecular configuration and restricted rotation in the solid state. Furthermore, a green OLED device fabricated with the dye containing N -butyl carbazole donor as dopant emitter (3%) in CBP host achieved good performance with high external quantum efficiency (4.2%), current efficiency (13.1 cd A −1 ) and maximum brightness (L max ) of 6180 cd m −2 . • Carbazole derivatives possessing two or three auxiliary donors and dicyanovinyl acceptor are synthesized and characterized. • They exhibited aggregation induced emission dependent on the nature and orientation of the auxiliary chromophore with the central core. • A green OLED device of a dye containing N -butylcarbazole donor exhibited high external quantum efficiency (4.2%).

Influence of 120 MeV Ag swift heavy ion irradiation on the optical and electronic properties of As-Se-Bi chalcogenide thin films

Ion beams of widely varying energies from keV to GeV have played a significant role in the modification of materials. The manuscript reports the influence of 120 MeV Ag swift heavy ion irradiation (SHI) at two different fluence on As40Se58Bi02 and As40Se45Bi15 thin films. The irradiation has shown strong impact on the optical constants like transmittivity, absorption coefficient, extinction coefficient, optical band gap and disorderness with no structural change. The optical transmittance decreased while absorption coefficient and extinction coefficient increased with increase in the fluence from 5 × 1012yions/cm2 to 5 × 1013ions/cm2. The decreased optical band gap with irradiation is explained on the basis of bond distribution model and density of defect states with increase in disorder. The p-type to n-type conductivity switching was observed at higher Bi content and the Hall measurement showed the increase in conductivity with irradiation. The Raman study on these ion irradiated films also confirmed no structural transformation. The surface morphological evolution of the films by Ag ion irradiation was studied by Field Emission Scanning Electron Microscopy.

Performance evaluation of nitrogen for fire safety application in aircraft

Fire suppression is an important safety certification requirement for aircraft as it is for all safety critical systems. Risk analyses are required at the design and certification stages to determine the probabilities and means of mitigating such risks. Apostolakis et al. (1995) shows an approach for spacecraft, Spyrou and Koromila (2020) for passenger ships and Arshi et al. (2010) for reactors. An important analysis tool for aircraft is the Zonal Analysis process (Chen and Fielding, 2018) Such analyses include investigation of means of fire suppression for which the use of Halon 1301 was a popular choice. The production of Halon and several halocarbons were banned under the Montreal Protocol in 1994, which necessitates an investigation for use of environmental-friendly agents for this application. The primary objective of this paper is to determine the ‘design concentration’11Design concentration is the volumetric concentration of the agent to achieve successful fire suppression in an enclosure. of nitrogen required for fire suppression. Computational Fluid Dynamics (CFD), in combination with experimental verification is described in this paper. The air flow rate in the cup-burner model was varied between 10 L/min and 40 L/min for a low-speed numerical model and was validated against the BS ISO 14520 cup burner test (BS ISO 14520 Annex, 2006) to determine the extinguishing concentration of nitrogen. The study revealed that the design concentration of nitrogen was 34% (14% oxygen concentration). Further investigation suggested that at low air flow rates (10 L/min and 20 L/min case), distortions produced in the flow led to erroneous measurement of oxygen concentration in experiments. The fire suppression model was extended to an n-heptane pool fire in a large enclosure. The recorded design concentration was approximately 39% additional nitrogen corresponding to 13% oxygen concentration by volume. It was observed that the weight of nitrogen required increased by 7.5 times compared to Halon 1301 use for this model. Future work can be explored in aircraft cargo and engine bay fire safety systems through Minimum Performance Standard (MPS) testing and simulations with nitrogen as the agent. Such work will feed directly into system safety assessments during the early design stages, where analyses must precede testing.

A first-principles theoretical study of the electronic and optical properties of twisted bilayer GaN structures

Gallium nitride (GaN) is a well-investigated material that is applied in many advanced power electronic and optoelectronic devices due to its wide bandgap. However, derivatives of its monolayer form, such as bilayer structures, have rarely been reported. We study herein the electronic and optical properties of GaN bilayer structures that are rotated in the plane at several optimized angles by using the density functional theory method. To maintain the structural stability and use a small cell size, the twisting angles of the GaN bilayer structures are optimized to be 27.8°, 38.2°, and 46.8° using the crystal matching theory. The band-structure analysis reveals that the bandgap is wider for the twisted structures compared with the nontwisted case. The simulation results provide the absorption coefficient, extinction coefficient, reflectivity, and refractive index at these angles. The spectra of all these optical properties match with the bandgap values. The simulated refractive index of the bilayer structures at all the twisting angles including 0° is smaller than that of bulk GaN, indicating a reduced scattering loss for optoelectronics applications. Considering the results of this analysis, the possible applications may include low-loss integrated electronic and optical devices and systems.

First-principles calculations of structural, electronic, and optical properties for Ni-doped Sb2S3

Antimony sulphide (Sb2S3) is a potential candidate for alternative material in solar cell application. The structural, electronic, and optical properties of Ni doped Sb2S3 were calculated using full potential linear augmented plane wave (FP-LAPW) based on popular density-functional theory (DFT). The equilibrium lattice parameters have been calculated using Perdew–Burke–Ernzerhof (PBE) generalized gradient approximation (PBE-GGA). The band structure and density of state for Ni-doped Sb2S3 have been determined using Tran Blaha modified Becke-Johnson (TB-mBJ) potential. Our results indicate that Ni doped Sb2S3 has lower band gap energy compare to pure-Sb2S3. The optical properties of Ni-doped Sb2S3 such as absorption coefficient, reflectivity, refractive index, energy-loss function and extinction coefficient are presented. The results demonstrate that Ni-doped Sb2S3 has higher optical absorption coefficient in the visible region than pure-Sb2S3 which is good for optoelectronic applications.

Cost‐Effective Green Synthesis of Boron‐Rich Carbide Coatings for Infrared Windows and Night‐Vision Optics

The increasing demand for infrared (IR) window materials for various applications in optical imaging systems necessitates the development of cost‐effective green techniques. Herein, the synthesis of refractory boron carbide (BC) using castor oil, as carbon precursor, and the preparation of IR transparent films by thermal vapor deposition technique is reported. Films are prepared with 1:3, 1:4, and 1:5 ratios of boric acid and castor oil, respectively. The X‐ray diffraction (XRD) and Fourier‐transform IR (FTIR) analyses reveal the structure of films prepared to be BC. The morphology of the films is analyzed by the atomic force microscopy (AFM) technique, and its dependence on precursor's ratio is also studied. The spectroscopic characterization by the ultraviolet–visible–near IR (UV–vis–NIR) transmittance study reveals the potential of the films for IR window applications. The bandgap energy of the BC films determined from the Tauc plot yields a value of 2.33 eV. The absorption coefficient, extinction coefficient, refractive index, dissipation factor, and optical conductivity are also studied from the reflectance and transmittance data.

Molecular design towards two-dimensional electron acceptors for efficient non-fullerene solar cells

Non-fullerene polymer solar cells (NF-PSCs) have gained wide attention recently. Molecular design of non-fullerene electron acceptors effectively promotes the photovoltaic performance of NF-PSCs. However, molecular electron acceptors with 2-dimensional (2D) configuration and conjugation are seldom reported. Herein, we designed and synthesized a series of novel 2D electron acceptors for efficient NF-PSCs. With rational optimization on the conjugated moieties in both vertical and horizontal direction, these 2D electron acceptors showed appealing properties, such as good planarity, full-spectrum absorption, high absorption extinction coefficient, and proper blend morphology with donor polymer. A high PCE of 9.76% was achieved for photovoltaic devices with PBDB-T as the donor and these 2D electron acceptors. It was also found the charge transfer between the conjugated moieties in two directions of these 2D molecules contributes to the utilization of absorbed photos, resulting in an exceptional EQE of 87% at 730 nm. This work presents rational design guidelines of 2D electron acceptors, which showed great promise to achieve high-performance non-fullerene polymer solar cells.

An Influence of the Peculiarities of the Concentration Field of Gaseous Fire Extinguishing Substances with High Boiling Point on Their Fire Extinguishing Properties

Behaviour of fluoroketone CF3CF2C(O)CF(CF3)2 as gaseous fire suppressant in various volumes was studied computationally and experimentally. It was showed that non-uniformity of the concentration field of fire extinguishing agent having high boiling point influences strongly its effectiveness: extinguishing concentration of the fluoroketone rises from 3.5 % vol. in the smallest volume (1 m3) up to 4.5 % vol. in 100 m3. Relatively uniform extinguishing medium was found in 1 m3 only. In bigger volumes a torus-like inhomogeneity with a reduced concentration of fire suppressant in the middle part of the room is formed. To compensate this effect it is necessary to increase the average concentration of the agent. More complex geometry of the experimental premise may cause appearance of long-term existing non-uniformity of extinguishing environment which is difficult to overcome by increasing the average concentration of fire suppressant or by increasing the discharge time. To obtain practically effective test results it is necessary to increase standard test chamber to 100 m3 (or more).

Effect of deposition method on the structural and optical properties of CH3NH3PbI3 perovskite thin films

In this study, methyl ammonium lead Iodide perovskite (CH3NH3PbI3≡MAPbI3) was deposited as a thin planar film on a glass substrate at room temperature using one-step and two-step methods. The effect of each method of preparation on the structural, morphological, and optical properties was investigated. The results show that the average size of the MAPbI3 crystallites are ~57.3 nm and 25.8 nm for the one and two-step methods, respectively. The pore-filling of the perovskite film is incomplete when using the one-step process but completely filled when two-step method was used. Therefore, both one-step and two-step methods lead to perovskite islands and void-free perovskite layers, respectively. Scanning emission microscopy images show that the quality of the film produced by two-step is much better than that formed via one-step. Moreover, the perovskite film prepared via one-step method tends to produce a higher pinhole density than two-step, and thus lower coverage that leads to a low absorption and a low absorption coefficient. Parameters such as optical absorption coefficient, refractive index, extinction coefficient, dielectric constant, and optical conductivity were also estimated. The intensities of both photoluminescence and amplified spontaneous emission spectra of MAPbI3 sample prepared via one-step method were found to be lower than those prepared via two-step.

Investigation of the effect of dimethyl methylphosphonate (DMMP) on flame extinction limit of lithium-ion battery electrolyte solvents

An experimental and numerical study was conducted to quantify the flame retardant effects of different DMMP addition loadings on the flame extinction limits of four lithium-ion battery electrolyte solvents. The minimum extinguishing concentration (MEC) of CO2, which was measured using the cup-burner method, was applied to characterize the flame retardant effects of different DMMP loadings. Then, a model based on the perfectly stirred reactor concept was constructed to calculate the MEC and interpret the measurements established in the cup-burner test. A comparison was conducted between the measured and calculated MECs of N2 and a satisfactory agreement was obtained. Further investigation found that DMMP could significantly improve the extinction temperature by clearing the H radical, suppressing the reaction temperature and increasing the sensitivity of temperature to reaction rate constants, which caused the decrease in the flame extinction limit of solvents. The experimental results showed that DMMP has a certain saturation effect on reducing the flame extinction limits of solvents. For the four solvents, the sensibilities of the flame extinction limits to the DMMP additions were different, which were ranked in the order of diethyl carbonate > ethyl methyl carbonate > dimethyl carbonate > ethyl acetate.

Effect Annealing Temperature on the Physical Properties of Cadmium Sulphide thin Films Deposited by using Thermal Evaporation Technique

This study measured some of the structural, electrical and optical properties of cadmium sulfide (CdS) thin films with thickness of 150 nm deposited on glass substrate by using thermal evaporation system under vacuum pressure 1x10−5mbar. X-ray diffraction technology was used to analyses the structural properties of the CdS films. Results showed that the CdS films type cube polycrystalline structure and the preferred growth path was [111].In evaluating DC conductivity, we observed two mechanism of activation energy. In the measuring Hall effect shows that the electrical conductivity of the CdS films is negative carriers (n-type). The result of the (AFM) measurements showed that the grain size and average roughness increased with annealing temperature increased. In optical properties it were found that transmittance 80% at RT that decreases with increasing annealing temperature. It also found that absorption coefficient, extinction coefficient and refraction index increased with increasing annealing temperature. Optical energy gap were found decreased with increasing annealing temperature as (RT, 150 and 300 C°) the results (2.4, 2.38 and 2.32 eV) respectively. The results electrical properties showed that the CdS thin films had two activation energy and Hall effect were found that the mobility increase with increasing annealing temperature.

Effect of Thickness on Structural, Morphological, and Optical Properties of Copper (Cu) Doped Zinc Selenide (ZnSe) Thin Films by Vacuum Evaporation Method

Effect of thickness on structural, optical and morphological properties of 2% copper (Cu) doped zinc selenide (ZnSe) thin films, grown onto chemically and ultrasonically cleaned glass substrate by thermal evaporation method in high vacuum (~10-6 Torr) were studied. Films of 100, 200, 300 and 400 nm thickness were prepared at 200℃ substrate temperature where annealing temperature and annealing time was fixed at 100℃ and 1 hour respectively. The X-ray diffraction (XRD) exhibited polycrystalline nature indicating the zinc-blende structure with a preferential orientation along the (111) plane of cubic phase. The grain size was found to be 19.27 nm. Dislocation density and microstrain were also found as 2.691 × 10-3 nm-2 and 1.85 × 10-3 respectively. Atomic Force Microscopy (AFM) study confirmed the growth of grains and their distribution over the entire surface of the films. All the films were characterized optically by UV-VIS-NIR spectrophotometer in the photon wavelength ranging from 300 to 1000 nm. The optical transmittance and reflectance were utilized to compute the absorption coefficient, extinction coefficient and band gap energy of the films. The calculated band gap energy was found to increase (2.99 to 3.94 ev) with varying thickness. The maximum transmittance was found to be 87.65% for the 400 nm film.
 Journal of Bangladesh Academy of Sciences, Vol. 43, No. 2, 159-168, 2019

Spray pyrolysis of graphene oxide based composite for optical and wettability applications

In this study, silica-graphene oxide nano–composites were prepared by sol-gel technique and deposited by spray pyrolysis method on glass substrate. The effect of changing the graphene/silica ratio on the optical properties and wetting of these nano–structures has been investigated. The structural and morphological properties of the thin films have been studied by x-ray diffraction spectroscopy (XRD), field emission scanning electron microscope (FESEM), energy dispersive x-ray spectroscopy (EDS) and atomic force microscope (AFM). XRD results show that silica structures present in the synthesized films exhibit amorphous character and there is a poor arrangement in graphene plates along their accumulation directions. The relationship between the contact angle of the water drop and the surface of thin films was analyzed by surface roughness. The results show that the contact angle is also decreased by decreasing the surface roughness. Absorption and transmittance spectra obtained from (UV–vis) of the studied films were used to compute and determine some optical parameters such as absorption coefficient, transmittance rate, optical gap, refractive index and extinction coefficient of the films. The calculated optical band gaps of films decrease by increase the silica contents in these structures.

Enhancement of the optical properties of copper sulfate crystal by the influence of shock waves

Abstract