Transmittance Values Research Articles

Colorful Semitransparent Organic Photovoltaics with Record Key Parameters by Optimizing Photon Utilization and Fabry‐Pérot Resonator Electrode

AbstractDonor PM6 and acceptor L8‐BO are employed to build semitransparent organic photovoltaics (ST‐OPVs). Opaque OPVs are fabricated by tuning the spin‐coating speed of PM6:L8‐BO solution to optimize the photon utilization by balancing photon harvesting and photogenerated carrier collection. The optimal opaque OPVs exhibit relatively high fill‐factor (FF) of 77.58% and power conversion efficiency (PCE) of 15.07%, the average visible transmittance (AVT) of corresponding PM6:L8‐BO films arrives to 53.25%, indicating great potential in realizing efficient ST‐OPVs. ST‐OPVs are built with 1 nm Au/(10, 15, 20, 25 nm) Ag as cathode, exhibiting the PCE/AVT of 11.53%/22.57%, 13.20%/14.24%, 14.28%/9.34%, and 14.71%/6.77%, respectively. Colorful ST‐OPVs are achieved by coupling different Ag/LiF/Ag Fabry‐Pérot (F‐P) resonator microcavity. Green ST‐OPVs with varied color coordinates are achieved by fixing LiF layer thickness as 110 nm and varying Ag layers′ thickness, originating from the adjusted transmittance spectra of green ST‐OPVs. Upon fixing Ag layers′ thickness as 15/25 nm and varying LiF layer thickness as 90, 110, and 145 nm, ST‐OPVs present colors of blue, green, and red with corresponding transmittance peak at 474, 553, and 657 nm. The corresponding PCE/peak transmittance (Tpeak) values arrive to 13.80%/37.8%, 13.31%/28.4%, and 13.20%/27.7%, which should be the best performance among reported colorful ST‐OPVs.

Effect of ionizing radiation on mechanical and damping properties of phenyl‐vinyl‐methyl‐polysiloxane elastomers cured with platinum

AbstractIn this study, phenyl‐vinyl‐methyl‐polysiloxane (PVMQ) elastomers were cured with a Pt catalyst and irradiated with different doses (0–80 kGy) using electron beams. Before irradiation studies, rheological analyses were carried out for the three different Platinum‐A (PtA)/Platinum‐B (PtB) ratios by using a Moving Die Rheometer. End of rheological and mechanical analyses 1/2 PtA/PtB ratio was chosen for irradiation studies. To examine the effect of absorbed dose on the mechanical properties of platinum‐cured PVMQ (Pt‐PVMQ) elastomers, stress–strain behavior, stress relaxation, and energy‐damping behavior at static conditions were investigated by cyclic compression analyses. The effect of absorbed dose on the stiffness, permanent deformation, and crosslink densities of Pt‐PVMQ elastomers was also examined. For the identification of the effect of irradiation on the vibration‐damping properties of Pt‐PVMQ elastomers, dynamic mechanical properties were investigated by using an elastomer testing system, and variation of transmissibility, stiffness, and tan delta values with frequency were examined. As a result of this study, the effect of ionizing radiation on the mechanical and dynamic properties of PVMQ elastomer cured with platinum catalyst has been revealed, and it has been shown that some of these properties can be altered with ionizing radiation. The results obtained in this study also showed that Pt‐PVMQ elastomers have higher damping properties than the damping behavior of Pt‐VMQ elastomers, and these Pt‐PVMQ elastomers can be defined as high damping systems.

Experimental Study on In-plane Stiffness of Track in a Turnout of the Railway in Vietnam

Aims: This study aims to determine the in-plane stiffness of the track in a turnout of the railway in Vietnam. Background: Track stiffness is a basic parameter of railway tracks that influences the bearing capacity of the track, the dynamic behavior of passing vehicles, the quality of track geometry, and the life of track components. Objective: The objective of this research is to determine the in-plane stiffness of the track based on substructure modulus, and rail pad stiffness at a track section in a turnout. Methods: Various tests which included the field tests of the substructure modulus, and rail pad stiffness tests in the laboratory were done. Substructure modulus was investigated at ten locations in the field. Rail pad stiffness was tested with five samples in the laboratory. In-plane stiffness of the track was calculated through substructure modulus and rail pad stiffness. The finite element method was used to evaluate the bearing capacity of bearings with different in-plane stiffness values. Results: Based on the results obtained, the substructure modulus was from 0.49 N/mm3 to 1.48 N/mm3. The rail pad stiffness is from 32.99 kN/mm to 34.92 kN/mm. These results are used to calculate the in-plane stiffness of the track. The in-plane stiffness of a track section in a turnout in Vietnam is from 25.18 kN/mm to 30.19 kN/mm. According to the finite element method, it is possible to determine the maximum value of forces transmission to the supports from 37.743 kN to 38.989 kN corresponding to the above stiffness values with the axle load of train 14 tons and rail P60. Conclusion: The stiffness of the supporting is proportional to the value of the force transmitted to the supporting. This study clearly showed that the substructure (soil and ballast) properties had the most impact on the total in-plane stiffness of the track. The results will be a tool for the track maintenance engineer to implement correct maintenance activities.

Transparent electromagnetic absorption film derived from the biomass derivate

Electromagnetic wave absorption materials featuring small thicknesses and wide effective absorption bandwidth (EAB) are highly required for next-generation portable devices, wearable electronics, and blooming military applications. However, traditional EM particle absorbents, such as carbon-based, magnetic metal-based, and MXene-based materials are always visible black, which severely hinders their utilization as microwave-stealth smart window alternatives. Therefore, it is a critical challenge to fabricate flexible windows simultaneously possessing high optical transmittance and excellent EM wave absorption properties. Herein, we prepared a transparent wood composite with an optical transmittance value of more than ∼83% through a delignification and polymer composite immersion method. The delignification process could remove the light-absorbing lignin component, and the transparent woods were realized by immersing the delignified wood into refractive-index-matched pre-polymerized acrylamide (AM) including minor silver nanowires, carbon nanotubes, and reduced graphene oxides. In addition, due to the presence of numerous polarization centers originating from hydrophilic functional groups and conductive fillers, the transparent wood composite showed superior EM absorption performance, and EAB can reach 9.5 GHz, almost occupying the whole X band (8.2–12.4 GHz) and Ku band (12.4–18 GHz) at a thickness of 2.0 mm. Furthermore, the transparent wood presented a great insulative thermal performance with a low thermal conductivity of 0.45 W m−1 K−1 (half of common glass). The developed transparent wood composites offered significant potential as smart energy-efficient windows with the expectation to survive military equipment and alleviate EM pollution.

Effect of Thickness and Translucency on Color Change and Masking Ability of Ceramic Materials used for Laminate Veneers.

This study evaluated the effect of the thickness and translucency of lithium disilicatebased glass ceramics on resin composite substrates on color change and masking effect. Laminate veneers were fabricated using IPS e.max CAD (A1) blocks with two different light transmittance values (High translucent [HT], Low translucent [LT]). Slices of two different thicknesses (0.3 mm, 0.5 mm) were obtained (n=10) and laminate veneers were cemented on the resin composite substrates of two different shades (A2, A3.5). The color change (ΔE values) was evaluated with the CIELab color system using a spectrophotometer, while the masking effect was calculated. The data were analyzed using independent-samples t-test and two-way analysis of variance. The ceramic thickness and translucency had a significant effect on final color and masking. When HT was used, and the laminate veneer thickness decreased (0.3 mm), the masking effect in ΔE values were lower (p⟨0.05). The ΔE values (⟩3.7) were clinically unacceptable. With the increase in thickness, translucency of porcelain laminate veneers decreases showing better color masking ability. Veneer thickness seems to be more effective on the restoration's masking ability than the shade of the substrate and translucency. Cinically, in case a 0.5-mm or thinner laminate veneer is planned, tooth color, resin cement and ceramic type should be considered.

Optimizing solar still performance through glass cover optical properties: A mathematical modeling and theoretical investigation

This research investigates the impact of the glass cover's optical properties on fresh water production in solar still desalination systems. By examining the transmissivity, absorptivity, and reflectivity of the glass cover under different operating conditions, the study aims to optimize the yield and efficiency of the desalination process. A validated mathematical model is developed, integrating energy and mass transfer with the glass cover's optical properties. For Matroh City, the research determines the optimal tilt angle of the glass cover (21.7°) and reveals absorptivity values ranging from 0.086 to 0.112, reflectivity values ranging from 0.076 to 0.89, and increasing transmissivity values from 0 to 0.84. Furthermore, a variable monthly optimal tilt angle outperforms a fixed annual tilt angle, resulting in a 2.5 % increase in annual distillate production. The results indicates that with an increase in glass thickness from 5 mm to 20 mm, the daily yield and efficiency decrease from 6.6 kg/m2 and 31.5 % to 5.2 kg/m2 and 24.9 %.This research provides valuable insights into the influence of glass cover optical properties on solar still desalination performance, contributing to renewable energy-based desalination processes. The implications extend to the development of sustainable water sources, greenhouse gas reduction, and addressing water scarcity challenges.

Impact of operating pressure and oxygen gas flow on the characteristics of zinc oxide coatings

The primary aim of this study is to examine the effects of various combinations of working pressure and oxygen gas flow on the properties of zinc oxide (ZnO) coatings. Well-crystalline ZnO coatings are formed by employing RF magnetron sputtering on silicon wafers and glass while varying the working pressure and oxygen gas flow. The structure of the thin film was analyzed using X-ray diffraction (XRD). According to the XRD data, the film's structure was made of ZnO, and the peak (002) was visible. Over the wavelength range of 300–800 nm, the optical transmittance of ZnO thin film was examined. The observed transmission value was on average 85 %. With the assistance of contact angle measurement equipment, the surface energy and contact angle of the developed coatings were both determined. Measured contact angles ranged from 96.6° to 115.3°, whereas the surface energy ranged from 14.08 to 25.11 mJ/m2. The enhancement of the anti-icing attributes was achieved by the modification of the operating pressure and gas flow during the deposition process of the coatings.

Scrutinate proclivity of regional aquifer hydraulic parameters: apriorisms for borehole failures within parts of the middle Benue Trough, Nigeria

Abstract Water borehole failures in Nigeria's middle Benue Trough are caused by imprecise aquifer features. This study employed empirical data to understand hydraulic parameters, anticipate regional groundwater potential, and explain borehole failures in difficult geological locations. 89 VES stations and quantitative data interpretation were required to determine the geoelectric properties beneath each station. Aquifer layers were delineated and their resistivity and thickness combined using geo-environment specific relations to yield transmissivity, hydraulic conductivity for both basement complex and sedimentary environments variously. Results show that aquifer resistivity ranges from 4.5 – 984.4 ohm-m; aquifer layer thickness varies from 4.4 m – 96.7 m with average thicknesses in sedimentary environment considerably greater; hydraulic conductivities range from 0.056 – 30.15 m/day, Transmissivity values range from 0.31 – 1281.36 m2/day. Log transformed transmissivity values range from 3.51 – 7.1 m2/day. Approximately 60.34% of the entire study area falls within transmissivity magnitude III and IV and can only support withdrawals for local water supply adequate for small communities and private consumption only and this may be the inferred cause for the low yield and high borehole failure rates. Understanding hydraulic characteristics is critical for 6controlling groundwater; research advances knowledge of transmissivity and conductivity in complex terrain.

Building for tomorrow: Analyzing ideal thermal transmittances in the face of climate change in Brazil

The climate will become hotter, and buildings will perform differently as outdoor conditions evolve. If the lowest energy demand is desired, it is crucial to determine the ideal thermophysical properties of the envelope over the buildings' life span. However, the scientific literature is still scarce in providing a compelling answer. Therefore, this study (i) determines ideal thermal transmittance values (U-values) for present-day and future climates, (ii) determines to what extent the thermophysical properties will need to change to remain ideal, (iii) identifies different trends of U-values over time, (iv) establishes a relationship between outdoor air temperatures, cooling and heating setpoints, and ideal U-values, and (v) proposes a set of design strategies according to each trend. The EPSAP generative design method was used to create a large dataset of residential buildings with random geometries and U-values to evaluate their energy demand for heating and cooling in EnergyPlus. The thermal performance of each building was evaluated for 30 locations in Brazil for the current period and two future timeframes (2050 and 2080). The Future Weather Generator tool was used to morph today's typical meteorological weather to match the EC-Earth3 data for the SSP5–8.5 scenario. Although climate change has a similar relative impact, its consequences differ over time in each location. The ideal U-values have different trends in different regions: (a) remaining unchanged in the future, (b) changing from being the highest possible to the lowest of the analyzed range in 2050 or 2080, and (c) being mid-range values in the present and with similar or lower values in the future climate. The impact on the thermal loads of maintaining the present-day ideal U-values also varies significantly in the future timeframes, from being nil to representing an increase reaching 30 % in 2050 (∆ 2.94 MW·h ± 0.06 MW·h) and 57 % in 2080 (∆ 6.05 MW·h ± 0.09 MW·h). Therefore, building design professionals need to use different strategies according to each region and consider how climate evolves during the lifetime of the building.

Wideband multimode smart modulator based on phase change materials

Optical components with switchable optical properties have garnered significant attention due to their wide range of potential applications in the fields of optical detection, radiative cooling, and energy conservation, etc. Most modulators focus on modulating a single parameter within a narrow spectral range, which often falls short of meeting the increasing demands of advanced photonic systems. In this study, we introduce a smart modulator capable of wideband modulation across three modes: transmission, absorption, and reflection. This modulation is triggered by the temperature-dependent phase transition of Vanadium dioxide (VO2) and In3SbTe2 (IST). We optimized the optical properties of the smart modulator using a combination of the Rigorous Coupled Wave Analysis method and Genetic Algorithm. As a result, we achieved average transmissivity, absorptivity, and reflectivity values of 0.785, 0.812, and 0.798, respectively, across the spectral range of 2.5 to 15 µm for each corresponding mode. Importantly, the multimode modulation performance remains excellent even at large incident angles. Furthermore, we demonstrate the exceptional performance of the smart modulator in practical applications, taking thermal fuses as an example. This showcases its effectiveness in thermal protection and modulation. The development of such wideband multimode smart modulators holds the potential to expedite the creation of compact, efficient, and multifunctional optical systems.

First-principles calculations to investigate the effect of X (X=B, Al, Ga) atomic substitution concentration on the electronic structure and optical properties of arsenene

The elastic properties, electronic structure, and optical properties of X ([Formula: see text], Al, Ga) atomic substitution for arsenene are calculated based on density functional theory. The results show that, at the same concentration, B-substituted arsenene shows the best structural stability, followed by Ga-substituted arsenene, with Al-substituted arsenene being the least. Arsenene and its substitution systems possess excellent mechanical stability. The substitution of X atoms leads to a reduction in the bulk modulus, shear modulus, and Young’s modulus of arsenene systems, while simultaneously increasing the Poisson’s ratio. For the substitution systems, the four parameters all gradually increase as the substitution concentration increases. The substitution of X ([Formula: see text], Al, Ga) atoms into arsenene can facilitate the transformation from an indirect to direct bandgap (except for Al and Ga substitution at a concentration of 3.13%) with a narrower bandgap for increasing substitution concentration. The B–As bond shows the strongest covalency, followed by the Ga–As bond, while the Al–As bond exhibits the strongest ionicity. Arsenene substituted with X atoms shows anisotropy of optical properties in both the xy-plane and along the z-axis direction. The static dielectric constant increases with higher substitution concentration. The imaginary part of the dielectric function shows the extent of excited electron transitions between bands. After X atom substitution, arsenene exhibits a redshift in its absorption edge, which is wider with the higher substitution concentrations. The peak reflectance and valley transmittance values of arsenene and its substitution systems are located in the ultraviolet region in both xy-plane and z-axis.

Study of solar cells structures based on perovskite and nanoparticles

Researchers and scientists working in the field of energy conversion have become interested in the rapidly developing new class of solar cells based on mixed organic-inorganic halide perovskite semiconductors over the past few years. Here we study the transmission of assumed solar cell structures based on nanoparticles and CH3NH3PbI3, CH3NH3PbBr3, and CH3NH3PbI2Br perovskite types by using the transfer matrix method (TMM). We found that as the nanoparticle volume fraction increases, the transmission decreases. Cells doped with aluminum nanoparticles showed the best transmission values. And transmission values in all wavelength ranges are better than those in the range of approximately (300-500).

Laser scanner and UAV digital photogrammetry as support tools for cosmic-ray muon radiography applications: an archaeological case study from Italy

The use of light detection and ranging technologies, i.e. terrestrial laser scanner (TLS), airborne laser scanner (ALS) and mobile laser scanner (MLS), together with the unmanned aerial vehicles digital photogrammetry (UAV-DP) and satellite data are proving to be fundamental tools to carry out reliable muographic measurement campaigns. The main purpose of this paper is to propose a workflow to correctly plan and exploit these types of data for muon radiography aims. To this end, a real case study is presented: searching for hidden tombs in the Etruscan necropolis of Palazzone (Umbria, Italy). A high-resolution digital elevation model (DEM) and three-dimensional models of the ground surface/sub-surface of the study area were created by merging data obtained using different survey methods to achieve the most accurate three-dimensional environment. Indeed, the simulated muon flux transmission used to infer relative transmission values, and the estimated density distribution, depends on the reliability of the three-dimensional reconstructed ground surface model. The aim of this study is to provide knowledge on the use of TLS and UAV-DP data and GPS-acquired points within the transmission-based muography process and how these data could improve or worsen the muon imaging results. Moreover, this study confirmed that muography applications require a multidisciplinary approach.

Electromagnetic near-field focusing based on metasurfaces

Near-field electromagnetic focusing has become a hot research topic due to its high application value in wireless transmission, wireless sensing, biomedicine, and radio frequency identification. In this paper, anisotropic metasurfaces have been proposed to manipulate the phase of the electromagnetic (EM) wave for obtaining EM near-field focusing. Under orthogonal linearly polarized incidence, dual focus functions can be realized independently for polarization multiplexing on the metasurfaces. Meanwhile, Single focus and multi focus with different energy distributions and focal position is obtained by the proposed metasurfaces. By using the Vivaldi antenna as the feed source positioning at the focal of the metasurfaces, a lens antenna with high gain is obtained with circularly polarized far-field mode and broadband characteristics. Due to the unique advantages of metasurfaces in modulating the phase distribution of EM waves, the proposed method may pave a new way for EM focusing application.

Supercapitance performance evaluation of MXene/Graphene/NiO composite electrode via in situ precipitation technique

In this study, we synthesize MXene/Graphene/NiO composite via the in situ precipitation technique. The CV plots exhibited redox peaks, which served as evidence of the presence of faradaic processes. We estimated the specific capacitances of MXene (Ti3C2TX), Graphene, and MXene/Graphene/NiO composite at scan rates of 10, 20, 30, 40, and 50 mV/s. The values obtained were 1250, 625, 416, 312, and 250 F/g for MXene, 972, 486, 324, 243, and 194 F/g for Graphene, and 1666, 847, 564, 423, and 338 F/g for the MXene/Graphene/NiO composite. The specific capacitance values obtained from GCD analysis are estimated to be 139.111, 183.244, 276.483, and 558.788 F/g for MXene (Ti3C2TX), Graphene, and MXene/Graphene/NiO composite, respectively. At a current density of 2.0 A/g, the energy densities obtained for MXene (Ti3C2TX), Graphene, and MXene/Graphene/NiO composite are 100.159, 100.159, and 100.159, respectively. The absorption rate of the graphene, MXene (Ti3C2Tx), and MXene/Graphene/NiO composite is between 0.02 and 0.21, 0.92 to 1.69, and 0.32 to 1.19 a.u. respectively. The graphene has a transmittance value of 90.4%, MXene (Ti3C2Tx) has a transmittance value of 10.3%, and MXene/Graphene/NiO composite has a transmittance value of 49.2%. In terms of energy bandgap, the graphene, MXene (Ti3C2Tx), and MXene/Graphene/NiO composite have values of 0.8, 1.59, and 1.75 eV respectively. The synthesized material has specific capacitances that are well-suited for high-performance energy storage devices.

Evaluation of aquifer parameters through integrated approach of geophysical investigations, pumping test analysis and Dar-Zarrouk parameters in the central part of Bari Doab, Punjab, Pakistan.

In the central part of Bari Doab in Punjab Province of Pakistan, the factors such as sporadic rainfall pattern, decrement of water in rivers, subsurface salinity and excessive mining of groundwater have badly affected the hydrogeology and recharge system of aquifer. The present research work is an endeavour to evaluate the characteristics and potential of aquifer for its future sustainable availability within the study area of central part of Bari Doab. The geophysical studies, pumping tests data, borehole logs and Dar-Zarrouk parameters were used integrally to evaluate the aquifer hydraulic and hydrologic parameters in the study area. VES technique of geophysical investigations using Schlumberger electrodes configuration was carried out at sparsely distributed 435 locations. Litho-logs and VES results altogether decipher that the subsurface alluvial succession is primarily composed of intermixed layers of sand, gravel, clay, silt and some kankar inclusions. The VES data allied with pumping test analysis of test wells in the study area were used to evaluate the aquifer hydraulic properties. Comparatively low values of discharge rate, hydraulic conductivity and transmissivity were evaluated in two wells whilst relatively higher values of these parameters were evaluated in rest of six wells. The results of hydrologic parameters also confirm the results of hydraulic parameters in the wells. Finally, the Dar-Zarrouk parameters were used for the estimation of hydraulic parameters for whole study area and the aquifer zones of relatively high and low potential were delineated.

Investigation and optimization of In-Vitro behaviour of Perovskite barium titanate as a scaffold and protective coatings

The piezoelectric effect is widely known to have a significant physiological function in bone development, remodeling, and fracture repair. As a well-known piezoelectric material, barium titanate is particularly appealing as a scaffold layer to improve bone tissue engineering applications. Currently, the chemical bath deposition method is used to prepare green synthesized barium titanate coatings to improve mechanical and biological characteristics. Molarity of the solutions, an essential parameter in chemical synthesis, is changed at room temperature (0.1–1.2 Molar) to prepare coatings. The XRD spectra for as deposited coatings indicate amorphous behavior, while polycrystalline nature of coatings is observed after annealing (300 °C). Coatings prepared with solutions of relatively low molarities, i.e. from 0.1 to 0.8 M, exhibit mixed tetragonal – cubic phases. However, the tetragonal phase of Perovskite barium titanate is observed using solution molarities of 1.0 M and 1.2 M. Relatively high value of transmission, i.e. ∼80%, is observed for the coatings prepared with high molarities. Band gap of annealed coatings varies between 3.47 and 3.70 eV. For 1.2 M sample, the maximum spontaneous polarization (Ps) is 0.327x10−3 (μC/cm2) and the residual polarization (Pr) is 0.072x10−3 (μC/cm2). For 1.2M solution, a high hardness value (1510 HV) is recorded, with a fracture toughness of 28.80 MPam−1/2. Low values of weight loss, after dipping the coatings in simulated body fluid, is observed. The antibacterial activity of BaTiO3 is tested against E. coli and Bacillus subtilis. Drug encapsulation capability is also tested for different time intervals. As a result, CBD-based coatings are a promising nominee for use as scaffold and protective coatings.

Temperature Sensing via Electromagnetically Induced Transparency Vapor

The behavior of multilevel atomic ensembles (e.g., alkali-metal atoms) can be influenced significantly by the intensity of a driving field (or controlling/coupling field). The phase coherence between two transition pathways driven by a probe light and a driving field can lead to the effect known as electromagnetically induced transparency (EIT). In EIT, the probe light can pass through a three-level alkali-metal atomic vapor without absorption or reflection when two coherent resonances (transition pathways driven by the driving and probe fields) are present and the linewidths of the transparency windows are sufficiently narrow. The optical characteristics of atomic systems can also be affected by the Doppler broadening of the absorption profile in a spectroscope. Our analysis indicates that both broadenings (related to the transitions excited by the driving and probe fields) can be expanded, leading to an increase in the transmittance and reflectance broadenings when a coupling field with adaptive strength is applied; the corresponding temperature would, thus, be implemented and readable. We show that the most suitable preparation for temperature sensing via an EIT vapor is to provide 80 times the spontaneous decay rate (SDR) of the excited atomic levels. This configuration results in reflectance and transmittance values that range between zero and one and cover a temperature range of 0 K to 600 K. As an example, we demonstrate the integration of specialized coating technologies with EIT ensembles for temperature sensing in the range of dozens of kelvins at and above room temperature. A key advantage of this temperature-sensing system is its ability to use adaptive resonant visible light as the probe field. This novel approach may find applications in providing unprecedented levels of precision and control in temperature sensing for coating processes and in the design of other photonic or optical devices. It can also be used to determine the temperature-dependent behavior of the specific heat of alkali-metal solids and gases (including the latent heats of vaporization or sublimation of alkali-metal solids) through the reflection and transmission spectra of the vaporized EIT atomic vapors.

Optical Absorption, Photocarrier Recombination Dynamics and Terahertz Dielectric Properties of Electron-Irradiated GaSe Crystals

Optical absorption spectra of 9 MeV electron-irradiated GaSe crystals were studied. Two absorption bands with the low-photon-energy threshold at 1.35 and 1.73 eV (T = 300 K) appeared in the transparency region of GaSe after the high-energy-electron irradiation. The observed absorption bands were attributed to the defect states induced by Ga vacancies in two charge states, having the energy positions at 0.23 and 0.61 eV above the valence band maximum at T = 300 K. The optical pump-terahertz probe technique (OPTP) was employed to study the dark and photoexcited terahertz conductivity and charge carrier recombination dynamics at two-photon excitation of as-grown and 9 MeV electron-irradiated GaSe crystals. The measured values of the differential terahertz transmission at a specified photoexcitation condition were used to extract the terahertz charge carrier mobilities. The determined terahertz charge carrier mobility values were ~46 cm2/V·s and ~14 cm2/V·s for as-grown and heavily electron-irradiated GaSe crystals, respectively. These are quite close to the values determined from the Lorentz–Drude–Smith fitting of the measured dielectric constant spectra. The photo-injection-level-dependent charge carrier lifetimes were determined from the measured OPTP data, bearing in mind the model injection-level dependencies of the recombination rates governed by interband and trap-assisted Auger recombination, bulk and surface Shockley–Read–Hall (SRH) recombination and interband radiative transitions in the limit of a high injection level. It was found that GaSe possesses a long charge carrier lifetime (a~1.9 × 10−6 ps−1, b~2.7 × 10−21 cm3ps−1 and c~1.3 × 10−37 cm6ps−1), i.e., τ~0.53 μs in the limit of a relatively low injection, when the contribution from SRH recombination is dominant. The electron irradiation of as-grown GaSe crystals reduced the charge carrier lifetime at a high injection level due to Auger recombination through radiation-induced defects. It was found that the terahertz spectra of the dielectric constants of as-grown and electron-irradiated GaSe crystals can be fitted with acceptable accuracy using the Lorentz model with the Drude–Smith term accounting for the free-carrier conductivity.

Considerations for determining the performance of ultraviolet light emitting diode fluid disinfection systems.

The International Ultraviolet Association (IUVA) Task Force was formed to develop guidelines regarding testing and reporting on performance of UV LED water disinfection systems. The goal was to provide clarity in a guidance document on measuring system performance across the global UV LED water disinfection system market. A review of current performance measurement protocols for mercury lamp based systems shows that the common elements of UV LED system performance measurement protocols should be as follows: specified standard for the amount of pathogen reduction required, the requirement that the validation testing be conducted by a competent facility, and that the system be continually monitored by UV sensors while in use to verify system performance unless pathogen reduction is not claimed. UV LEDs have selectable peak wavelengths, as opposed to mercury lamps that have fixed emission wavelength values. As a result of this difference, the following changes to protocols used to test mercury lamp systems are recommended. First, the use of disinfection benchmarks other than 254 nm dose, such as direct inactivation values, dose benchmarks referenced to 254 nm, and/or dose benchmarks at the UV LED emission wavelength that give the same inactivation as the original 254 nm UV dose benchmark. Second, the use of 254 nm UV water transmittance values as a placeholder, rather than an assumed correct value, for systems under test with LED wavelengths >250 nm and water transmittance values ≥87%. More research is needed for lower wavelengths and UVTs. Third, the recommendation that germicidal response UV sensors be used in UV LED based systems to ensure that the validated disinfection is delivered. Finally, additional LED-specific considerations were also noted. UV LEDs are also instant-on devices, making them ideal light sources for systems operated intermittently. Performance testing of systems operated intermittently should include a test to insure that pathogens do not migrate past the UV LEDs while the LEDs are off. UV LED devices have recognized protocols for determining the lifetime of the devices, as well as for measuring other device properties. Caution should be exercised in using these lifetime values for devices in UV disinfection systems, since the thermal environment of the devices may be different for protocol testing and disinfection system operation. PRACTITIONER POINTS: Validation of UVC LED fluid disinfection is necessary for point of use, point of entry, and municipal applications. The emission spectrum properties, considerations and measurements for output over lifetime, and unique system design considerations of UVC LEDs as light sources are factors that must be considered when evaluating fluid disinfection performance. The instant-on operation, system geometry, validation benchmarks, system sensing, water transmittance, and fouling must also be considered for UVC LED devices when evaluating fluid disinfection performance.