Light Path Length Research Articles

Performance Improvement of Triplet-Triplet Annihilation-Based Upconversion Solid Films through Plasmon-Induced Backward Scattering of Periodic Arrays of Ag and Al.

The performance improvement of solid-state triplet-triplet annihilation-based photon upconversion (TTA-UC) systems is required for the application to various solar devices. The performance can be improved by making use of the local strong electric field generated through the excitation of localized surface plasmon (LSP) resonance of metal nanostructures. However, since the improvement is effective only within the limited nanospace around nanoparticles (i.e., the near-field effect), a methodology for improving the performance over a wider spatial region is desirable. In this study, a significant improvement in the threshold light excitation intensity (Ith) (77% decrease) as the figure of merit and the upconverted emission intensity (6.3 times enhancement) in a solid-state TTA-UC film with a thickness of 3 μm was achieved by stacking the film with periodic Ag half-shell arrays. The highest-enhanced upconverted emission was obtained by tuning the diffuse reflectance peak, which results from the excitation of LSP resonance of the Ag half-shell arrays, to overlap well with the photoexcitation peak of the sensitizer in the TTA-UC film. The intensity of the enhanced upconverted emission was independent of the distance between the lower edge of the TTA-UC film and the surface of half-shell arrays in the nanometer order. These results suggest that the performance improvement was attributed to the photoexcitation enhancement of the sensitizer by elongating the excitation light path length inside the TTA-UC film, which was achieved through a strong backward scattering of the incident light based on the LSP resonance excitation (i.e., the far-field effect). In addition, the upconverted emission was improved using half-shell arrays comprising low-cost Al, although the enhancement factor was 3.5, which was lower than that of Ag half-shell arrays. The lower enhancement may be attributed to a decrease in the backward scattering of the excitation light owing to the intrinsic strong interband transition of Al at long visible wavelengths.

Enhancing sensitivity in absorption spectroscopy using a scattering cavity

Absorption spectroscopy is widely used to detect samples with spectral specificity. Here, we propose and demonstrate a method for enhancing the sensitivity of absorption spectroscopy. Exploiting multiple light scattering generated by a boron nitride (h-BN) scattering cavity, the optical path lengths of light inside a diffusive reflective cavity are significantly increased, resulting in more than ten times enhancement of sensitivity in absorption spectroscopy. We demonstrate highly sensitive spectral measurements of low concentrations of malachite green and crystal violet aqueous solutions. Because this method only requires the addition of a scattering cavity to existing absorption spectroscopy, it is expected to enable immediate and widespread applications in various fields, from analytical chemistry to environmental sciences.

Effect of 1-D silver grated electrode on wafer‐based TOPCon c-Si solar cell

A modified structure of Anti reflection coating (ARC) less wafer based 200 μm thick c-Si Solar cell with tunnel oxide passivated contact (TOPCon) solar cell is proposed with 1-Dimensional silver grated rear electrode. The light diffraction mechanism increases the light path length, which improves the absorption of photons in the absorber layer. An effective investigation mechanism using numerical simulator is used to study the absorption and reflection with perfectly matched boundary conditions for higher accuracy of result. The performance enhancement of TOPCon solar cell with the variation in oxide thickness is observed and effect of 1-D silver grating in designed cell is examined. Maximum absorption is achieved using optimum rear electrode grated structure. The performance of the modified rear electrode SCs are compared with similar Si solar cell design methodology to show the effectiveness of modifications. The modified Si SC shows 160 % and TOPCon solar cell exhibits 190 % enhancement in the current density with optimized silver grated rear electrode. Similarly, an improved efficiency of 9.26 % for modified silver grated Si solar cell and maximum efficiency of 20.8 % is achieved for TOPCon solar cell with 1-D grated rear electrode.

Relating Near-Infrared Light Path-Length Modifications to the Water Content of Scattering Media in Near-Infrared Spectroscopy: Toward a New Bouguer-Beer-Lambert Law.

In near-infrared spectroscopy (NIRS), the linear relationship between absorbance and an absorbing compound concentration has been strictly defined by the Bouguer-Beer-Lambert law only for the case of transmission measurements of nonscattering media. However, various quantitative calibrations have been successfully built both on reflectance measurements and for scattering media. Although the lack of linearity for scattering media has been observed experimentally, the sound multivariate statistics and signal processing involved in chemometrics have allowed us to overcome this problem in most cases. However, in the case of samples with varying water content, important modifications of scattering levels still make calibrations difficult to build due to nonlinearities. Moreover, even when calibration procedures are successfully developed, many preprocessing methods used do not guarantee correct spectroscopic assignments (in the sense of a pure chemical absorbance). In particular, this may prevent correct modeling and interpretation of the structure of water. In this study, dynamic near-infrared spectra acquired during a drying process allow the study of the physical effects of water content variations, with a focus on the first overtone OH absorbance region. A model sample consisting of aluminum pellets mixed with water allowed us to study this specifically, without any other absorbing interaction terms related to the dry mass-absorbing constituents. A new formulation of the Bouguer-Beer-Lambert law is proposed, by expressing path length as a power function of water content. Through this new formulation, it is shown that a better and simpler prediction model of water content may be developed, with more precise and accurate identification of water absorbance bands.

Circular dichroism spectroscopy of DNA duplexes at near-biological concentrations

Circular dichroism (CD) of nucleic acids has been typically carried out at sample concentrations below 10 μM, which is far lower than nucleic acid concentrations in biological systems. Attempts to study nucleic acid conformations by CD at higher concentrations using 10 and 1 mm pathlength cuvettes led to instrument artifacts. By shortening the light pathlength to around 0.1 mm, we herein report the first CD profiles of nucleic acids at sub-mM concentrations, which are relevant to nucleic acid concentrations in cellular cytoplasm and nucleus. These CD experimental conditions will allow future conformational studies of nucleic acids under biologically relevant conditions.

Two-dimensional monitoring of air pollution in Madrid using a Multi-AXis Differential Optical Absorption Spectroscopy two-dimensional (MAXDOAS-2D) instrument

Abstract. Trace gases play a key role in the chemistry of urban atmospheres. Therefore, knowledge about their spatial distribution is needed to fully characterize air quality in urban areas. Using a new Multi-AXis Differential Optical Absorption Spectroscopy two-dimensional (MAXDOAS-2D) instrument, along with an inversion algorithm (bePRO), we report the first two-dimensional maps of nitrogen dioxide (NO2) and nitrous acid (HONO) concentrations in the city of Madrid, Spain. Measurements were made during 2 months (6 May–5 July 2019), and peak mixing ratios of 12 and 0.7 ppbv (parts per billion by volume) for NO2 and HONO, respectively, were observed in the early morning in the southern part of the downtown area. We found good general agreement between the MAXDOAS-2D mesoscale observations – which provide a typical spatial range of a few kilometers – and the in situ measurements provided by Madrid's air quality monitoring stations. In addition to vertical profiles, we studied the horizontal gradients of NO2 in the surface layer by applying the different horizontal light path lengths in the two spectral regions included in the NO2 spectral analysis: ultraviolet (UV, at 360 nm) and visible (VIS, 477 nm). We also investigate the sensitivity of the instrument to infer vertically distributed information on aerosol extinction coefficients and discuss possible future ways to improve the retrievals. The retrieval of two-dimensional distributions of trace gas concentrations reported here provides valuable spatial information for the study of air quality in the city of Madrid.

Effects of UV Light Path Length and Wavelength on UV/Chlorine versus UV/H2O2 Efficacy

Inconsistent trends have been reported in the relative competitiveness of UV/chlorine and UV/H2O2 advanced oxidation processes for micropollutant degradation during drinking water treatment at benc...

Improving light and CO2 availability to enhance the growth rate of the diatom, Chaetoceros muelleri

Diatoms (Bacillariophyceae) are an important source of feed for juvenile animals in aquaculture hatcheries. Increasing the yield of feed cultures by optimizing illumination and inorganic carbon supply could significantly reduce operational costs for hatcheries. In this study, the growth dynamics and photosynthetic efficiency of the aquaculture-relevant diatom Chaetoceros muelleri were monitored and modelled under four different light and CO2 conditions. By increasing the availability of both light and CO2, a growth rate of 1.59 ± 0.12 (day−1) was achieved for C. muelleri, an increase of approximately 89% compared to 0.84 ± 0.08 (day−1) which was recorded in cultures under light limitation with no CO2 addition. The real-time monitoring and modelling of growth dynamics and photosynthesis rates in different light and CO2 conditions have demonstrated that light availability can be improved by minimizing the path length of light through the culture, and the importance of on-demand CO2 supply. The techniques and results outlined in this study could be used to potentially improve biomass production in hatcheries.

Giga-Bit Transmission Between an Eye-Safe Transmitter and Wide Field-of-View SiPM Receiver

In this paper, the performance of a wide field of view VLC receiver that includes a silicon photomultiplier (SiPM) is reported. In particular, a receiver field of view of ±45° and On-Off keying data rates of 1.8 Gbps are demonstrated in 500 lux of ambient light. These results are achieved by combining optical absorption filters with a 6 mm by 6 mm SiPM. By absorbing ambient light between 450 nm and 750 nm these filters ensure that the SiPM is not saturated and reduces the transmitter power needed to support the required data rate. Unlike other optical filters the performance of absorption filters is not sensitive to angle of incidence. Consequently, the FOV is explained by a combination of the changes to the receiver’s projected area, the path length of light in the filters and reflections from the filter surfaces. In addition, the results of the calculations, described by the IEC 62471:2006 safety standard, needed to determine the eye safety of a transmitter are reported. These calculations and the resulting irradiance levels available in a representative office scenario are used to show that data rates of more than 1 Gbps could be achieved with eye safe transmitters.

The optimal utilization of lighting factor in the flat photobioreactor for biological applications

Distribution of light intensity in the flat photobioreactor for microalgae cultivation as a step design for production of bio-renewable energy was addressed in the current study. Five sizes of bioreactors with specific distances from the main light source were adopted as independent variables in experiential design model. The results showed that the bioreactor’s location according to the light source, determines the nature of light intensity distribution in the reactor body. However, the cross-section area plays an important role in determining the suitable location of reactor to achieve required light homogeneity. This area could change even the expected response of the light passing through the reactor if Beer-Lambert's law is adopted. In addition, the increase in path length of light inside the bioreactor reduces the amount absorbed by the liquid per unit volume. Finally, the study concluded that these factors represent a basic pillar in the reactor design stages, in order to achieve a homogeneous distribution of lighting with cost-effective.

Enhancing the efficiency of polymer solar cells by embedding Au@Ag NPs Durian shape in buffer layer

Organic semiconducting polymers are useful in several photonic applications due to their tunable optical and electronic properties and ease of fabrication. However, due to the short exciton diffusion length and low carrier mobility of polymer solar cell (PSC) materials, their power conversion efficiency (PCE) is comparably lower than their inorganic counterparts. Therefore, this study introduces plasmonic effects into these organic polymer-based solar cells by incorporating Au@Ag nanoparticles (NPs) to improve their performance. The plasmonic NPs (Au@Ag durian-shaped NPs), which can be placed in the hole transport layer (HTL) of the PSC, scatter light into the active layer thereby increasing the optical path length of the incident light, leading to higher absorption and short circuit current density of the PSCs. The shape of nanoparticles is an important factor since it directly affects surface plasmonic resonance (SPR) and the incident light’s scattering. The proposed Au@Ag NPs (with many sharp spikes) confirmed the effect of small radii of the spike ends of the durian-shaped NPs on the performance PSCs. The results reveal that the embedded Au@Ag NPs improve the electrical properties of both the active layer and HTL in PSCs. In more detail, Au@Ag NPs create plasmon-electrical effects which shorten transport path length of the low-mobility holes and lengthen that of high-mobility electrons for better-balanced carrier collection. Meanwhile, the resistance of HTL is reduced by Au@Ag NPs. Therefore Jsc and PCE of up to 17 mA/cm2 and 3.73%, respectively, implies a 44.4% improvement in short-circuit photocurrent density and 49% enhancement of the power conversion efficiency compared to the reference cell.

Practical application of microsphere samples for benchmarking a quantitative phase imaging system.

Quantitative phase imaging (QPI) provides an approach for monitoring the dry mass of individual cells by measuring the optical pathlength of visible light as it passes through cells. A distinct advantage of QPI is that the measurements result in optical path length quantities that are, in principle, instrument independent. Reference materials that induce a well‐defined optical pathlength shift and are compatible with QPI imaging systems will be valuable in assuring the accuracy of such measurements on different instruments. In this study, we evaluate seven combinations of microspheres embedded in index refraction matching media as candidate reference materials for benchmarking the performance of a QPI system and as calibration standards for the optical pathlength measurement. Poly(methyl metharylate) microspheres and mineral oil were used to evaluate the range of illumination apertures, signal‐to‐noise ratios, and focus positions that allow an accurate quantitative optical pathlength measurement. The microsphere‐based reference material can be used to verify settings on an instrument that are suitable for obtaining an accurate pathlength measurement from biological cells. The microsphere/media reference material is applied to QPI‐based dry mass measurements of a population of HEK293 cells to benchmark and provide evidence that the QPI image data are accurate.

Pilot-scale removal of microcontaminants by solar-driven photo-Fenton in treated municipal effluents: Selection of operating variables based on lab-scale experiments

This study aimed to assess the removal efficiency of microcontaminants (namely: acetaminophen, diclofenac, carbamazepine, caffeine, sulfamethoxazole, trimethoprim) spiked in water by solar-driven photo-Fenton using Fe:Ethylenediamine-N, N′-disuccinic acid (1:1), focusing especially on improving operating parameters. These parameters were first studied at lab scale (1–4 L): (i) Fe3+ concentration; (ii) liquid depth; (iii) water matrix (natural water and real municipal wastewater treatment plant effluent). The best conditions were then evaluated outdoors under natural radiation in a pilot-scale solar photoreactor (90 L) treating real municipal wastewater treatment plant effluent evaluated by HPLC/QqLIT-MS. Diclofenac was the most efficiently degraded at lab scale and it was shown that the light pathlength did not affect the degradation rate but deeper liquid enables more treatment capacity. Fe:EDDS at 1:1 and iron concentration at 0.054 mM was sufficient for MC removal efficiency up to 97 %. All microcontaminants (46 microcontaminants were detected) were efficiently removed in the pilot-scale under the best conditions determined at lab scale. Therefore, a well-designed, simple, low-volume and low-cost lab-scale photoreactor and a selected mixture of microcontaminants at close to real concentrations would enable selection of the operating parameters of a large solar photo-Fenton application.

Consecutive removal of heavy metals and dyes by a fascinating method using titanate nanotubes

Titanate nanotubes TNT are promising materials for water treatment due to properties. Sodium titanate nanotubes (Na-TNT) were hydrothermally synthesized and characterized using XRD, FESEM, HRTEM, Zeta potential, nitrogen adsorption and desorption, and FT-IR spectra techniques. The efficiency of Na-TNT for adsorption of Ni(II) from water was tested through different conditions including pH, Na-TNT dose, initial metal concentration, and contact time. The results showed efficient adsorption performance with rapid removal of 90 % of Ni(II) ions within the first 15 min and after 30 min, the equilibrium was attained with removal efficiency close to 100 % at pH = 7 and with an adsorption capacity of 181.2 mg/g. Ni-TNT was collected and recycled for the removal of methylene blue (MB) by combined adsorption and photocatalytic degradation. The adsorption efficiency reached (99.5 %) and the equilibrium adsorption capacity was 916 mg/g and 330 mg/g for Ni-TNT and Na-TNT respectively. The correlation coefficient R2, error function Chi2, SSE, and MSE were used to evaluate the best fit models to the experimental data. The adsorption mechanism was explored using density functional theory and Monte Carlo simulation. The photocatalytic activity of Ni-TNT was tested through two different types of experiments. More attention was paid to the effect of the light path length through the dye solution and the effect of the experiment container dimensions on the photocatalytic degradation process. Also, both Na-TNTs and Ni-TNTs showed potent antifungal and antimicrobial activity. This work successfully represents TNT as a multifunctional material.

Effective Photon Management of Non-Surface-Textured Flexible Thin Crystalline Silicon Solar Cells

Summary Thin crystalline silicon (c-Si) showing outstanding flexibility has been considered as an active material for flexible solar cells. However, an effective photon management should be developed for thin c-Si, which shows severe light absorption loss. Here, we introduce random inverted-pyramidal polydimethylsiloxane (RIP-PDMS) films on the surface of the thin c-Si solar cell to simultaneously secure high absorption and flexibility. Attaching the RIP-PDMS film on the front surface of the device can significantly reduce surface reflection; near-infrared light recycling can be further improved by attaching a metal-coated RIP-PDMS film on the rear surface of the device. Notably, thin c-Si solar cells with RIP-PDMS films have an efficiency of 18.4% and exhibit a constant efficiency during 1,000 repeated bending tests with a bending radius of 10 mm. Also, finite-difference time-domain simulations confirm that the RIP-PDMS films increase the light diffusion and optical path length inside the c-Si.

Light Trapping in Single Elliptical Silicon Nanowires.

Light trapping in single nanowires (NWs) is of vital importance for photovoltaic applications. However, circular NWs (CNWs) can limit their light-trapping ability due to high geometrical symmetry. In this work, we present a detailed study of light trapping in single silicon NWs with an elliptical cross-section (ENWs). We demonstrate that the ENWs exhibit significantly enhanced light trapping compared with the CNWs, which can be ascribed to the symmetry-broken structure that can orthogonalize the direction of light illumination and the leaky mode resonances (LMRs). That is, the elliptical cross-section can simultaneously increase the light path length by increasing the vertical axis and reshape the LMR modes by decreasing the horizontal axis. We found that the light absorption can be engineered via tuning the horizontal and vertical axes, the photocurrent is significantly enhanced by 374.0% (150.3%, 74.1%) or 146.1% (61.0%, 35.3%) in comparison with that of the CNWs with the same diameter as the horizontal axis of 100 (200, 400) nm or the vertical axis of 1000 nm, respectively. This work advances our understanding of how to improve light trapping based on the symmetry breaking from the CNWs to ENWs and provides a rational way for designing high-efficiency single NW photovoltaic devices.

Improving acceptance rate of QoS-guaranteed point-to-multipoint traffic flows in elastic optical networks

Abstract This paper studies the load-balanced routing and admission control for point-to-multipoint traffic flows in elastic optical networks (EONs). EONs have emerged as a promising technology to provide high capacity for next-generation networks. Elastic bandwidth allocation promotes the spectrum utilization efficiency. We consider the problem of constructing bandwidth-guaranteed trees for on-demand point-to-multipoint session requests. A request is accepted, if a multicast tree with sufficient bandwidth on each link can be established. The main objective is to increase the multicast acceptance rate in the network. For this purpose, we propose an efficient scheme, namely optical load-balanced multicast routing with admission control (OLMR-AC), to improve the wavelength resources utilization in the network. As an advantage, OLMR-AC jointly considers both distance and congestion factors to create a multicast session. For each admitted session, a bandwidth–guaranteed steiner tree is provided in which not only the source node has a minimum-cost path to each receiver, but also its overall cost is minimal. The proposed scheme distributes the on-demand traffic flows over the available links fairly. Simulation results show the efficiency of the OLMR-AC algorithm in terms of multicast acceptance rate, average length of lightpaths, throughput, number of transmissions, and load variance.

New red phosphor ceramic K2SiF6:Mn4+

Abstract A new transparent ceramic phosphor for use in LED lighting has been fabricated. The previously reported and optimized narrow-emitting red phosphor, K2SiF6:Mn4+ (KSF), has been consolidated into a transparent ceramic phosphor for the first time, accomplished via hot-pressing the feedstock phosphor powder in a die under vacuum. KSF ceramics were fabricated with varying doping concentrations of Mn4+ and their properties studied. The absorption and emission spectra of the ceramics were identical to the feedstock phosphor powders and are ideal for LED lighting with strong absorption at 450 nm and narrow emission around 630 nm. The absorbance of the ceramics was directly proportional to the doping concentration. The ceramics were excited at various blue light fluxes and their emission intensities measured to study the effect of Mn4+ concentration on intensity-driven “droop” in the emission output. The ceramics with a lower Mn4+ doping were more efficient under higher light fluxes due to a decrease in Auger upconversion losses. KSF ceramics can allow a much longer path length of the diode light through the phosphor, as compared to phosphor-in-silicone, enabling the use of low optical absorption and the associated reduced activator concentration. The ceramics are measured to have a thermal conductivity of ~1.0 W/m-K, higher than that of phosphor-in-silicone or phosphor-in-glass. Several of these properties make KSF ceramics potentially desirable for use in white light LEDs. Greater thermal conductivity helps with heat dissipation, the lower surface area of the ceramic compared to the powder minimizes the environmental vulnerability of KSF, and the ability to lower the Mn4+ concentration reduces Auger recombination losses and mitigates the temperature rise, particularly at higher light flux.

Investigation of Aerosol Peak Height Effect on PBL and Volcanic Air Mass Factors for SO2 Column Retrieval from Space-Borne Hyperspectral UV Sensors

We investigate the effects of aerosol peak height (APH) and various parameters on the air mass factor (AMF) for SO2 retrieval. Increasing aerosol optical depth (AOD) leads to multiple scattering within the planetary boundary layer (PBL) and an increase in PBL SO2 AMF. However, under high AOD conditions, aerosol shielding effects dominate, which causes the PBL SO2 AMF to decrease with increasing AOD. The height of the SO2 layer and the APH are found to significantly influence the PBL SO2 AMF under high AOD conditions. When the SO2 and aerosol layers are of the same height, aerosol multiple scattering occurs dominantly within the PBL, which leads to an increase in the PBL SO2 AMF. When the APH is greater than the SO2 layer height, aerosol shielding effects dominate, which decreases the PBL SO2 AMF. When the SO2 and aerosol layers are of the same height under low AOD and solar zenith angle (SZA) conditions, increased surface reflectance is found to significantly increase the PBL SO2 AMF. However, high AOD dominates the surface reflectance contribution to PBL SO2 AMF. Under high SZA conditions, Rayleigh scattering contributes to a reduction in the light path length and PBL SO2 AMF. For volcanic SO2 AMF, high SZA enhances the light path length within the volcanic SO2 layer, as well as the volcanic SO2 AMF, because of the negligible photon loss by Rayleigh scattering at high altitudes. High aerosol loading and an APH that is greater than the SO2 peak height lead to aerosol shielding effects, which reduce the volcanic SO2 AMF. The SO2 AMF errors are also quantified as a function of uncertainty in the input data of AOD, APH, and surface reflectance. The SO2 AMF sensitivities and error analysis provided here can be used to develop effective error reduction strategies for satellite-based SO2 retrievals.

Rapid calcification propensity testing in blood using a temperature controlled microfluidic polymer chip.

Phosphate toxicity is a major threat to cardiovascular health in chronic kidney disease. It is associated with oxidative stress, inflammation and the accumulation of calcium phosphate commonly known as calcification in soft tissues leading to functional disorders of blood vessels. An improved calcification propensity test for the assessment of phosphate toxicity was developed, which measures the velocity of calcium phosphate mineralization from colloidal precursors in vitro. This so called T50 test measures the transformation from a primary into a secondary form of nanosized colloidal plasma protein-calcium phosphate particles known as calciprotein particles. The T50 test in its previous form required a temperature controlled nephelometer and several hours of continuous measurement, which precluded rapid bed side testing. We miniaturized the test using microfluidic polymer chips produced by ultrasonic hot embossing. A cartridge holder contained a laser diode for illumination, light dependent resistor for detection and a Peltier element for thermo control. Increasing the assay temperature from 37°C to 75°C reduced the T50 test time 36-fold from 381 ± 10 min at 37°C to 10.5 ± 0.3 min at 75°C. Incorporating sputtered micro mirrors into the chip design increased the effective light path length, and improved signal-to-noise ratio 9-fold. The speed and reproducibility of the T50 chip-based assay run at 75°C suggest that it may be suitable for rapid measurements, preferably in-line in a dialyser or in a portable microfluidic analytic device with the chip inserted as a disposable cartridge.