Small Absorption Coefficient Research Articles

Geometrical, elastic, electronic, phonon, and optical properties of Na3AgO2 from first-principles calculation

In this paper, the geometrical, elastic, electronic, phonon, and optical properties of Na3AgO2 have been systematically studied by first-principles calculation. The results show that Na3AgO2 is mechanically stable and has small compressibility. Na3AgO2 is an indirect band-gap semiconductor with weak interatomic interaction. The bandgap calculated by HSE06 is 2.314 eV, and that calculated by GGA is 1.261 eV. For Na3AgO2, in the valence band near the Fermi level, the curve peaks of TDOS at −2.11 eV and −0.885 eV are primarily composed of O 2p states, which hybridize the 4 d and 4p states of Ag. The conduction band mainly consists of the 4p, 4 d, and 5s states of Ag, while hybridizing a few 2p states of O and a few 2p and 3s states of Na. As can be seen from the phonon dispersion spectrum there is no negative phonon frequency in the whole Brillouin region, indicating the structure is stable. Mulliken bond population of Na3AgO2 shows that O–Ag bonds have strong covalency, O–Na bonds have strong ionic properties, Na–Na bonds and Na–Ag bonds are antibonding. Na3AgO2 has a small reflectivity and a small absorption coefficient in the direction of (100) and (010) and has good transparency. The transparency of blue-violet light in the (001) direction is not as good as that of low-energy visible light. The obtained results lead to the conclusion that Na3AgO2 is a promising p-type transparent conducting material and is expected to be applied in practice.

Effective third harmonic generation of 355 nm ultraviolet laser based on the borate-phosphate Ba3(ZnB5O10)PO4 crystal

An effective third harmonic generation (THG) 355 nm laser in a novel Ba3(ZnB5O10)PO4 (BZBP) crystal was demonstrated. Based on the phase matching (PM) calculation, the BZBP crystal has the type-I PM angle of θ = 90°, ϕ = 73.2° for generating the THG 355 nm laser, with a large acceptance angle of 66.3 mrad·mm and a small walk-off angle of 6.06 mrad. Using a nanosecond 1064 nm laser as the pump source, the THG 355 nm laser could achieve the maximum conversion efficiency of 28.4%, and the highest output power of 0.56 W. In addition, BZBP crystal also has a small weak absorption coefficient of 20-40 ppm/cm and a laser damage threshold of 1.04 GW/cm2. The achieved results indicate that the BZBP crystal is a promising UV nonlinear optical material due to its short absorption edge (180 nm), small walk-off effect, large acceptance angle, and non-hygroscopicity.

Absorption coefficients and scattering losses of TGG, TGP, KTF, FS, and CeF3 magneto-optical crystals in the visible via cavity ring-down spectroscopy.

We demonstrate a method for determining small absorption coefficients and surface-scattering losses of crystals using cavity ring-down spectroscopy and perform measurements on magneto-optical crystals of terbium gallium garnet (TGG), terbium gallium phosphate (TGP), fused silica (FS), potassium terbium fluoride (KTF), and C e F 3 at 532 and 634nm. Surface scattering is distinguished from absorption losses by using crystals of different lengths. A figure of merit (FoM) for magneto-optical crystals is defined to evaluate their suitability as intracavity optics in optical cavity applications. It is found that TGP has the highest FoM for crystal lengths up to ∼10m m, whereas C e F 3 and FS potentially outperform TGP for longer crystals. Single-pass applications are also briefly discussed.

Synthesis and Characterization of Amorphous Selenium, Cadmium and Silver Selenide Thin Films on Polyamide-6

Increasing photon absorption by capturing light is an important way to increase the efficiency of photovoltaic devices. In this regard, the small optical band gap (Eg) and high absorption coefficient of Se-containing thin nanofilms make them ideal for next generation photovoltaic devices based on selenides. Amorphous selenium was introduced into polyamide-6 (PA 6) via a chemical synthesis in a bath and the influence of the products of its reaction with Cd2+ and Ag+ ions on the film phase composition, topographic and optical properties were evaluated. AFM data have revealed that the surface roughness of the a-Se/PA 6 composite noticeably increases compared to that of unreacted PA 6. However, at later stages of film deposition, the roughness decreases, and the thin film becomes smoother and uniform. The incorporation of solid inorganic nanoparticles into flexible polyamide network causes chain stretching, which has been confirmed by ATR-FTIR spectroscopy data. The data of X-ray diffraction analysis, depending on the stage of synthesis, showed the crystalline composition of the film with peaks of Se8, CdSe, Ag2Se and Ag, which may explain the observed optical properties. The optical properties of the composites indicate a shift in the band gap from 4.46 eV for PA 6 to 2.23–1.64 eV upon the stepwise deposition of amorphous Se, CdSe and Ag2Se. Eg is conveniently located in the visible region of solar energy, making the obtained nanofilms ideal for solar energy harvesting.

Semi-transparent, high-performance lead-free Cs3Bi2I9 single crystal self-driven photodetector

All-inorganic Bi-based perovskites have attracted much attention due to their excellent stability, environmentally friendly, and low-cost solution processability. However, due to the large exciton binding energy and small light absorption coefficient, the performance of the Bi-based perovskite photodetector (PD) is far behind of the traditional Pb-based perovskite PDs. In this work, the lead-free all-inorganic Cs3Bi2I9 (CBI) perovskite single crystal was synthesized by a space-confined antisolvent-assisted crystallization method for high-performance, semi-transparent, and self-driven PDs with an ITO/SnO2/CBI/PTAA/Au/ITO structure. Electrical and optical properties of Au/ITO transparent electrode were studied considering its figure of merit and device quantum efficiency through optimizing the Au thickness. Finally, our optimized semi-transparent device showed excellent self-driven performance with a large on/off ratio of ∼5700, a high responsivity of 52.06 mA/W, a high detectivity of >1012 Jones, and a large linear dynamic range of up to 140.7 dB. In addition, our device demonstrated excellent characteristics to the weak light detection and the long-term stability. The Au/ITO electrode was adopted and tailored to balance the device performance and transparency, which provides a good route for developing high-performance and transparent devices in the future.

Source of Bright Near-Infrared Luminescence in Gold Nanoclusters.

Gold nanoclusters with near-infrared (NIR) photoluminescence (PL) have great potential as sensing and imaging materials in biomedical and bioimaging applications. In this work, Au21(S-Adm)15 and Au38S2(S-Adm)20 are used to unravel the underlying mechanisms for the improved quantum yields (QY), large Stokes shifts, and long PL lifetimes in gold nanoclusters. Both nanoclusters show decent PL QY. In particular, the Au38S2(S-Adm)20 nanocluster shows a bright NIR PL at 900 nm with QY up to 15% in normal solvents (such as toluene) at ambient conditions. The relatively lower QY for Au21(S-Adm)15 (4%) compared to that of Au38S2(S-Adm)20 is attributed to the lowest-lying excited state being symmetry-disallowed, as evidenced by the pressure-dependent antispectral shift of the absorption spectra compared to PL, yet Au21(S-Adm)15 maintains some emissive properties due to a nearby symmetry-allowed excited state. Furthermore, our results show that suppression of nonradiative decay due to the surface "lock rings", which encircle the Au kernel and the surface "lock atoms" which bridge the fundamental Au kernel units (e.g., tetrahedra, icosahedra, etc.), is the key to obtaining high QYs in gold nanoclusters. The complicated excited-state processes and the small absorption coefficient of the band-edge transition lead to the large Stokes shifts and the long PL lifetimes that are widely observed in gold nanoclusters.

Effect of gas radiation-depended natural convection on the transition of spatially developing boundary layers

In this study, the effect of natural convection affected by gas radiation on a spatially developing boundary layer was investigated through large-eddy simulations to evaluate the interaction between natural convection and thermal radiation in an open environment, wherein Tollmien–Schlichting instabilities dominate. The gas radiation was calculated using the discrete ordinate method considering gray gas as the medium, and the effect of the absorption coefficient of the medium on the boundary layer has been discussed. With gray gas medium with small and large absorption coefficient values, a turbulent boundary layer was observed, while with intermediate absorption coefficient values, little turbulence was observed. As the gas heated due to radiation, the thermal boundary layer thickness increased. With the thickening of the thermal boundary layer, the magnitude of the velocity gradient at the inflection point decreased, stabilizing the flow and damping the thermal boundary layer fluctuations owing to the Tollmien–Schlichting mechanism. The transition to turbulence of the boundary layer could be reduced when the fluid far from the heated wall was heated through thermal radiation and the shear stress at the infection point decreased. These results provide insights for the control of turbulence for natural convection.

Low-frequency sound absorption of a tunable multilayer composite structure

Our work investigates a tunable multilayer composite structure for applications in the area of low-frequency absorption. This acoustic device is comprised of three layers, Helmholtz cavity layer, microperforated panel layer, and the porous material layer. For the simulation and experiment in our research, the absorber can fulfill a twofold requirement: the acoustic absorption coefficient can reach near 0.8 in very low frequency (400 Hz) and the range of frequency is very wide (400–3000 Hz). In all its absorption frequency, the average of the acoustic absorption coefficient is over 0.9. Besides, the absorption coefficient can be tunable by the scalable cavity. The multilayer composite structure in our article solved the disadvantages in single material. For example, small absorption coefficient in low frequency in traditional material such as microperforated panel and porous material and narrow reduction frequency range in acoustic metamaterial such as Helmholtz cavity. The design of the composite structure in our article can have more wide application than single material. It can also give us a novel idea to produce new acoustic devices.

Conversion efficiency of resonant cavity enhanced narrow bandgap interband cascade photovoltaic cells

By combining an interband cascade (IC) configuration with an optical cavity, a novel approach to achieve efficient narrow bandgap photovoltaic (PV) cells is proposed. The proposed resonant cavity enhanced (RCE) ICPV cells can significantly alleviate the challenging issues in narrow bandgap semiconductor materials, which include a small absorption coefficient, a short diffusion length, and a high dark current density. Through simulations with realistic material parameters based on InAs/GaSb superlattice heterostructures, RCE ICPV cells are capable of achieving a conversion efficiency that exceeds 60%, which is much higher than what can be achieved with any other approach, especially with materials of a bandgap smaller than 0.3 eV. By varying structure parameters such as the absorber thickness, number of cascade stages, and the top mirror reflectance, we demonstrate how an RCE ICPV cell can be constructed to achieve an optimized device performance with high conversion efficiency. Also, a design example of a practical RCE narrow bandgap ICPV cell is provided.

The Substituent-Induced Symmetry-Forbidden Electronic Transition Allows Significant Optical Limiting under Weak Sky-Blue Irradiance.

We report a novel material containing a rare metal-free dopant chromophore with controlled electronic symmetry, which exhibits strong optical limiting (OL) capabilities under weak, continuous, sky-blue irradiance. Electron-donating substituents at positions C2 and C7 of pyrene allow significant triplet generation because of the symmetrically forbidden transition between the ground state and the lowest singlet excited state, which leads to accumulation of triplet excitons in the dopant chromophore. This also leads to a small ground state absorption coefficient and induces greater absorption of sky-blue wavelengths when triplet excitons of the chromophore accumulate. Consequently, molecular glass doped with the designed chromophore displays stronger OL characteristics compared with those of the rare element-containing glass that previously demonstrated the greatest OL performance under continuous sky-blue irradiance at sunlight power levels. The described approach to developing cost-effective, state-of-the-art OL materials is crucial for nonlinear optical applications working at a large scale under sunlight or room lights.

Scattering of the squeezed coherent light by a metamaterial slab with negative refractive index and hyperbolic metamaterial

In this paper, by using the quantum input-output relations for an anisotropic slab, we investigate the quadrature squeezing and Mandel parameter of the transmitted squeezed coherent state through a metamaterial slab with negative refractive index and also a hyperbolic metamaterial slab. It will be shown that the nonclassical properties of the aforementioned state decrease sharply in passing through the negative refractive index slab. While, the hyperbolic metamaterial slab with a small absorption coefficient can somewhat retain the nonclassical properties of the incident squeezed light.

Broadband second-harmonic and sum-frequency generation with a long-wave infrared laser in AgGaGe5Se12.

Using an 8 µm long-wave infrared laser as the fundamental wave, we achieved second-harmonic generation (SHG) and sum-frequency generation simultaneously in AgGaGe5Se12 and obtained a 4 µm laser output. Among them, SHG was achieved in the 173 nm spectral range of the fundamental wave, which was consistent with theoretical calculations. The average power of the obtained 4 µm laser was 41 mW, corresponding to an optical-to-optical conversion efficiency of 3.2%. The measured temperature acceptance bandwidth (LδT) (FWHM) was 50 K·cm; the angular acceptance bandwidth (Lδθ) (FWHM) was 13.3 mrad·cm; and the average absorption coefficient in the wavelength range of 0.86-11.30 µm was 0.07cm-1. In addition, the spectral acceptance bandwidth (Lδλ) of fundamental wave in AgGaGe5Se12 SHG and the spectral gain bandwidth of frequency downconversion in AgGaGe5Se12 were calculated. In view of the small absorption coefficient, the large temperature acceptance bandwidth, and the large spectral gain bandwidth, we conclude that AgGaGe5Se12 is a suitable nonlinear crystal for high-power short/mid/long-wave infrared lasers and frequency conversions of nanosecond-femtosecond infrared lasers. These results are conducive to the further development of AgGaGe5Se12 lasers.

CO2 Laser Photoacoustic Spectrometer for Measuring Acetone in the Breath of Lung Cancer Patients

A CO2 laser has the advantages of being high in power and having many laser lines in the 9–11 µm infrared region. Thus, a CO2 laser photoacoustic spectrometer (PAS) can have a multi-component measurement capability for many gas compounds that have non-zero absorption coefficients at the laser lines, and therefore can be applied for measuring several volatile organic compounds (VOCs) in the human breath. We have developed a CO2 laser PAS system for detecting acetone in the human breath. Although acetone has small absorption coefficients at the CO2 laser lines, our PAS system was able to obtain strong photoacoustic (PA) signals at several CO2 laser lines, with the strongest one being at the 10P20 line. Since at the 10P20 line, ethylene and ammonia also have significant absorption coefficients, these two gases have to be included in a multi-component measurement with acetone. We obtained the lowest detection limit of our system for the ethylene, acetone, and ammonia are 6 ppbv, 11 ppbv, and 31 ppbv, respectively. We applied our PAS system to measure these three VOCs in the breath of three groups of subjects, i.e., patients with lung cancer disease, patients with other lung diseases, and healthy volunteers.

Extraordinary Strong Band‐Edge Absorption in Distorted Chalcogenide Perovskites

All existing solar cell materials including hybrid perovskites show rather small absorption coefficient (α) of ≈104 cm−1 in the bandgap (Eg) transition region. The weak band‐edge light absorption is an essential problem, limiting conversion efficiency particularly in a tandem solar cell. Herein, all distorted chalcogenide perovskites (BaZrS3, SrZrS3, BaHfS3, and SrHfS3) are found experimentally to exhibit extraordinary high α exceeding 105 cm−1 near Eg, indicating the highest band‐edge α among all known solar cell materials. The giant absorption in the Eg region, which is consistent with the first principles, arises from the intense p–d interband transition enabled by dense S 3p valence states. For solar cell application, low‐gap BaZrS3 derivatives, Ba(Zr,Ti)S3 and BaZr(S,Se)3, are further synthesized. Among the possible candidates of top‐cell materials, an earth‐abundant and nontoxic Ba(Zr,Ti)S3 alloy shows great potential, reaching a maximum potential efficiency exceeding 38% in a chalcogenide perovskite/crystalline Si tandem architecture.

Structural, optical and electrical characterization of SnS nanomaterials grown at different temperatures

SnS nanocrystals were synthesized by simple wet chemical precipitation method. XRD results shows that the crystals are orthorhombic in phase. TEM images indicate that the grain sizes are almost spherical within the range 5 nm to 10 nm. Crystalline natures of the samples were confirmed by HRTEM. AFM analysis shows that surface roughness were found to be moderate. EDAX analysis revealed that the samples are maintained good stoichiometric ratio of Sn/S. From UV–Vis absorption spectra it is evident that SnS nanocrystals are good absorbing materials for solar light. PL spectra indicate a red shift of SnS nanocrystals occurred with increase growth temperature. Time correlated single photon counting (TCSPC) measurements revealed that PL decay life times are in the order of picosecond. The temperature varying SnS nanocrystals were p-type in nature with electrical conductivities were ranging from 0.020 to 0.037 Ohm−1 cm−1 and carrier concentrations were 7.05 × 1013 cm−3 to 1.54 × 1014 cm−3. Carriers drift mobilities were found to be high compared to the reported results. Therefore, SnS nanocrystals having low resistivity, higher drift mobility, higher carrier concentrations, small PL decay life time and high absorption coefficient exhibited excellent properties for the fabrication of optoelectronic devices.

Experimental model to describe the dielectric response of different dye and nanoparticles doped hydrogels for biological cell membranes and biological systems

Doped hydrogels with Methylene-Blue (MB), Rhodamine-B (RB), MB/RB dyes and NiFe2O4 nanoparticles (NPs) were developed as an experimental model to describe the dielectric/electric response of lipid matrix in biological cell membranes and biological systems. Hydrogels synthesized by polymerization technique are highly suitable for three-dimensional cell models due to biocompatible structure. Frequency and bias voltage evolution of dielectric and electrical parameters for all samples have been characterized by the impedance spectroscopy at room temperature (RT). Absorbance spectrum and energy band gap for all samples have been analyzed with UV–Vis absorption spectroscopy. The frequency and applied bias voltage dependence of experimental dielectric/electric properties for all samples were attributed to the basis of Kroop's theory, Maxwell-Wagner approach, viscoelastic mechanism and the micro Brownian motion of free ions. It was obtained that the absorbance spectrum values for all samples are associated with Lambert-Beer-Bouguer's law and innervation of the dipolar oscillations/quadrupoles of dye and NPs ions. The smallest and highest values of the absorption spectra were recorded for MB/RB dye and NiFe2O4 NPs doped hydrogels with respectively. Results from the complex impedance based Cole-Cole plots and their Smith Chart adaptation showed that MB/RB dye doped hydrogels has the largest semi-circle due to it has the highest relaxation times and the smallest absorption coefficient. The NiFe2O4 NPs doped hydrogels with the highest absorption value were found to be the most suitable samples for optoelectronic applications in the biological cell membranes. The MB/RB dye doped hydrogels were concluded to be the most suitable material for impedance applications due to have the greatest relaxation time in the Cole-Cole plots. It determined that all of all samples except RB doped hydrogels are exhibited Ohmic behaviour from the I-V characteristic analysis. The conductivity properties (from the power law exponent) in 1th region, the 2nd region and the 3rd region for dyes/NiFe2O4 NPs doped hydrogels were associated with the dc conductivity, the Correlated Barrier Hoping (CBH)/Quantum Mechanical Tunnel (QMT) conductivity and the Correlated Barrier Hoping model with respectively. It is concluded that RB dye doped hydrogels can be used as a model for biomedical devices and drug delivery system applications, because they have the highest dielectric and superior conductivity properties. Also, different cationic dyes and NiFe2O4 NPs doped hydrogels were found exciting in applications such as low-cost bio-flexible sensors, green electronics and health monitors that have in low-voltage-operating.

Enhancement of the refractive index modulation in a modulator based on GaAs/AlGaAs quantum wells

Approaches of optimization of coupled quantum wells with pronounced quantum-confined Stark effect in order to reach a high refractive index change are described. A numerical simulation was used to determine the optimal design parameters (quantum well width, barrier thickness and composition) based on GaAs/AlGaAs materials with two symmetric quantum wells, which provides the maximum modulation of the refractive index at a small absorption coefficient. It is demonstrated that, with the electric field strength varied within the range 0–20 kV cm−1 at an optical loss for interband absorption not exceeding 10 cm−1, the refractive index can be changed by up to 0.0362.

Limiting factors and efficiencies of narrow bandgap single-absorber and multi-stage interband cascade thermophotovoltaic cells under monochromatic light illumination

In this work, the factors that limit the conversion efficiency of narrow bandgap thermophotovoltaic (TPV) cells are identified and their impact on device performance is explored through studying their effects on key aspects such as quantum efficiency (QE), fill factor, open-circuit voltage, and voltage efficiency. These factors are closely associated with short carrier lifetime, high dark saturation current density, small absorption coefficient, and the limiting effects of diffusion length on the collection of photogenerated carriers. Calculations are carried out for narrow bandgap InAs/GaSb superlattice materials to illustrate how the conversion efficiency is limited by these factors for specific material parameters such as the product of absorption coefficient α and diffusion length L. We show that the multistage interband cascade (IC) architecture is capable of circumventing the diffusion length limitation to overcome the problem of a low QE in conventional single-absorber TPV cells, thereby enhancing the conversion efficiency by about 10% in wide ranges of αL and bandgaps with the particle conversion efficiency approaching 100%. The enhancement of conversion efficiency with the multistage IC architecture is especially significant with small αL, which is more than double of that in the single-absorber TPV cell. Also, the device performance dependence on the illumination source is investigated, which demonstrates flexibilities and advantage of the multistage IC architecture to achieve its maximum conversion efficiency with the energy of incident photons near the bandgap of absorbers. Finally, the future directions are discussed in terms of what can be further improved or need to be addressed with the remaining issue for the development of narrow bandgap TPV cells.

Impact of Structural Parameters on the Auditory Perception of Musical Sounds in Closed Spaces: An Experimental Study

This study attempts to investigate the impact of structural parameters (volume, shape, and the wall absorption coefficient) in closed space on the auditory perception of three different musical sound types. With binaural audibility technology and room impulse response measurement (RIR), this paper first verifies the reliability of using ODEON software in simulating simplified closed-space auditory scenes. Then, 96 music binaural signals produced in eight simulated closed spaces with different structural parameters are synthesized. Finally, auditory perception experiment is conducted on the synthesized binaural signals by using pair comparison method, and variance analysis is also made on the experimental results. It is concluded that (1) a hemispherical cabin with a small volume and large wall sound absorption coefficient is most suitable for playing a single instrument, such as the flute or violin, and (2) a cabin with large volume is suitable for playing multiple instruments music such as symphony, but the walls should not be totally reflective. The experimental scheme and results of current study provide guidance for designing the inner structure of the concert hall to achieve preferable auditory perception in practice.

Influence of pump-beam parameters and crystal optical properties on propagation of thermally affected Bessel–Gaussian beams generated by a solid-state laser

In diode-pumped solid-state laser system, the generation and propagation of Helmholtz–Gaussian beam families such as Bessel–Gaussian (BG) beam can dramatically suffer from the effects of heat load. In this study, based on the ABCD matrix for BG beams passing through a graded-index medium, expressions for the thermal lens focal length and the output beam are obtained. Furthermore, to evaluate the impact of the pump-beam parameters and crystal optical properties, the intensity distribution of the zeroth- and first-order BG beams against radial distance together with its corresponding transverse intensity pattern on X–Y plane under different pump powers, pump beam waists, absorption coefficients, and thermal conductivities are simulated and compared. The simulation results indicate that for powerful narrow pump beam, the thermal-induced effects are so dramatic that the intensity profiles are altered, as the discernment of BG beams is not easily feasible; however, taking into account the large pump waist, high thermal conductivity and small absorption coefficient can partly cause the laser output similar to non-thermal one despite high pumping power is received. Therefore, the precise selection of laser parameters can considerably reduce the effects of induced heat on the generation and propagation of BG beams. The obtained results are a valuable hint to experimenters for beam identification and beam quality monitoring.