Calculation Of Quantum Efficiency Research Articles

Enhanced Photocatalytic H2 Evolution Performance of the Type-II FeTPPCl/Porous g-C3N4 Heterojunction: Experimental and Density Functional Theory Studies.

It is of great significance to improve the photocatalytic performance of g-C3N4 by promoting its surface-active sites and engineering more suitable and stable redox couples. Herein, first of all, we fabricated porous g-C3N4 (PCN) via the sulfuric acid-assisted chemical exfoliation method. Then, we modified the porous g-C3N4 with iron(III) meso-tetraphenylporphine chloride (FeTPPCl) porphyrin via the wet-chemical method. The as-fabricated FeTPPCl-PCN composite revealed exceptional performance for photocatalytic water reduction by evolving 253.36 and 8301 μmol g-1 of H2 after visible and UV-visible irradiation for 4 h, respectively. The performance of the FeTPPCl-PCN composite is ∼2.45 and 4.75-fold improved compared to that of the pristine PCN photocatalyst under the same experimental conditions. The calculated quantum efficiencies of the FeTPPCl-PCN composite for H2 evolution at 365 and 420 nm wavelengths are 4.81 and 2.68%, respectively. This exceptional H2 evolution performance is because of improved surface-active sites due to porous architecture and remarkably improved charge carrier separation via the well-aligned type-II band heterostructure. Besides, we also reported the correct theoretical model of our catalyst through density functional theory (DFT) simulations. It is found that the hydrogen evolution reaction (HER) activity of FeTPPCl-PCN arises from the electron transfer from PCN via Cl atom(s) to Fe of the FeTPPCl, which forms a strong electrostatic interaction, leading to a decreased local work function on the surface of the catalyst. We suggest that the resultant composite would be a perfect model for the design and fabrication of high-efficiency heterostructure photocatalysts for energy applications.

Photoemission from GaAs-based photocathodes with multilayer complex structures

To enhance the near-infrared response of photocathodes in the application of image detection, two kinds of multilayer complex structures of GaAs-based photocathodes are developed by changing the structure of the buffer layer underneath the emission layer, wherein one is the graded bandgap structure, and the other is the distributed Bragg reflector (DBR) structure. The theoretical quantum efficiency suitable for the reflection-mode (r-mode) GaAs-based photocathode with these two kinds of buffer structures are deduced based on one-dimensional continuity equations, among which the reflectivity changing with the wavelength of incident light is considered in particular. By comparison of spectral characteristics of photocathodes with the two different structures, and analysis of cathode structure parameters, it is found that the photoelectric performance of the photocathodes with the two structures are quite different, and the structure parameters especially the thickness of GaAs emission layer have a great impact on the spectral characteristic. The quantum efficiency of photocathode with graded bandgap structure is improved due to the introduction of the built-in electric field and the decrement of interface recombination, while for cathode with DBR structure, the quantum efficiency is improved by the multiple reflection of light between two parallel mirrors in the stack of alternating quarter-wave layers of high and low refractive. The theoretical quantum efficiency calculation and analysis would provide theoretical guidance for the better design of GaAs-based photocathodes.

Photo-induced Electron Emission of Nanostructured Carbon Thin Film Based Transmission Photocathodes at Different Electric Field

Very thin nanostructured carbon films were deposited on quartz substrate by reactive magnetron sputtering using graphite target and gas mixture of Ar and reactive gas N_2 or N_2+H_2. Film thicknesses were in the range of 20-25 nm. Rutherford backscattering spectrometry and Elastic recoil detection analytical method determined the concentration of elements in the films. Scanning electron microscopy scanned the surface morphology of carbon films. Raman spectroscopy was used for chemical structural properties determination of very thin carbon films. Raman spectra intensities were fitted with Gaussian peaks. The photo-induced (pulsed laser - 266 nm) electron emission properties of very thin nanostructured carbon films were investigated by the measurement of cathode bunch charge at different electric field and calculate quantum efficiency. The influence of different electric field on the photo-induced electron emission characteristics of prepared transmission photocathodes are discussed.

Au surface plasmon resonance promoted charge transfer in Z-scheme system enables exceptional photocatalytic hydrogen evolution

Highly efficient photocatalytic water reduction to evolve hydrogen can be achieved by the construction of Z-scheme systems that mimics natural photosynthesis. However, coupling appropriate semiconductors with suitable water reduction potential still remains challenging. Herein, we report a novel Z-scheme system, based on the Au decorated 5,10,15,20-tetrakis(4-trimethylammoniophenyl) porphyrin tetra(p-toluene sulfonate) functionalized iron-doped carbon nitride. We prepared carbon nitride by varying the amount of iron dopant and then functionalized with porphyrin to obtain heterostructure photocatalyst. Owing to the strong interfacial contact and proper band alignment, a Z-scheme system is fabricated. Finally, we deposited Au nanoparticles over the surface of the as-fabricated Z-scheme system to promote the surface redox properties via efficient charge carrier’s separation and transfer. The 3Au-3 P/30Fe-CN photocatalyst achieved excellent H2 evolution activity by producing 3172.20 µmol h−1 g−1 under UV–visible irradiation. The calculated quantum efficiencies for 3Au-3 P/30Fe-CN photocatalyst at 365 and 420 nm irradiation wavelengths are 7.2% and 3.26%, respectively. The experimentally observed efficiency of our photocatalyst is supported by the density functional theory simulations in terms of the lowest work function and strong electrostatic interaction among the constituents of Z-scheme system.

Influence of ion beam surface treatment on the emission performance of photocathodes.

Photocathodes are mainly used in such hi-tech fields as photoelectric conversion devices, radiation detection, and accelerators. Laser-driven photocathodes are characterized by low emission, high brightness, easy control, rapid response, etc., and are hopeful to become satisfactory electron sources for next-generation high-frequency miniaturized electric vacuum microwave devices, to effectively improve the performance and rapid response capability of the devices. For this reason, based on previous research efforts on photocathodes, we proposed an idea that ion beam surface treatment technology was used to modify the substrate surface of photocathodes and make the surface textured, enhancing the light absorptivity and alkali metal adsorption performance of photocathodes, so as to improve their emission performance. The surface appearance of photocathodes was analyzed using the scanning electron microscope (SEM) method, and it was found that the surface of oxygen-free copper treated by ion bombardment had a nanocone structure. The photoemission characteristics of photocathodes before and after the treatment of the surface of oxygen-free copper were studied. Before and after the treatment, the maximum photoemission current densities under stable emission performance of the photocathode were 60.5 mA cm−2 and 146.0 mA cm−2, respectively, and the calculated quantum efficiencies were 2.67 × 10−3 and 1.71 × 10−2, respectively. The quantum efficiency of the photocathode was increased by 5.41 times after the ion surface treatment. The results show that the photoemission quantum efficiency of the oxygen-free copper surface was increased greatly after modification. It was believed through analysis that the main cause for the increase in quantum efficiency was the enhancement of light absorptivity and the increase in the emission surface area.

Assessing quantitatively charge carrier fate in 4-chlorophenol photocatalytic degradation using globular titania catalysts: Implications in quantum efficiency calculation

The complex interplay between photons and catalytic powders in liquid-phase photocatalytic degradation reactions requires combined computational and experimental approaches to render a quantitative assessment of the light harvesting and handling properties the system. The full assessment of the light-to-chemical efficiency is here presented for the first of time for the complex 4-chlorophenol degradation. The reaction is carried out under different illumination conditions (UV, visible) with advanced, globular titania catalysts displaying high activity with respect to P25 and other reference materials. A critical issue, up to know not accounted for in the literature, is the effect that the different reaction products exerts in the use of charge carrier species by the catalytic system. Quantifying light effects in chemical conversion with explicit analysis of kinetically-relevant charge carrier species fate drives to correction(s) of the quantum efficiency observable, with a magnitude up to ca. 100%. The work outlines a novel and general procedure for the quantitative assessment of the real number of photons used in transforming pollutants through any liquid-phase photocatalytic process.

Synthesis, characterization and optical spectroscopy of GdPO4 :Er3.

A series of Er3+ -doped GdPO4 phosphors was synthesized using a conventional solid-state reaction. The monazite structure (space group P121 /n1 ) of the obtained materials was confirmed using X-ray diffraction and Fourier transform infrared spectroscopy. Their optical spectra (excitation, emission, absorption, decay curves) were measured at room temperature in the visible and near-infrared (NIR) regions. The UV-visible-NIR optical absorption spectrum of GdPO4 :7% Er3+ was analyzed based on Judd-Ofelt (J-O) theory and the J-O intensity parameter (Ω2 , Ω4 , Ω6 ) was calculated. J-O intensity parameters were used to evaluate spontaneous emission properties such as branching ratios, transition probabilities, and radiative lifetime. The calculated quantum efficiency of the 1.5 μm emission (4 I13/2 -4 I15/2 ) was calculated to be 89%. This result proved that GdPO4 :Er3+ is suitable for use in optical amplifiers and is a potential host for laser applications. The most interesting transitions, located at about 540 nm, and 1.0 and 1.5 μm were investigated as a function of doping level and of temperature, to assess the conditions needed for the highest emission performance and to explore the range of application, in particular in the fields of lighting, thermal sensing, and of phosphors for bio-imaging.

A new blue-light pumped red-emitting NaYSnMoO7: Eu3+ pyrochlore phosphor for solid-state lighting

A new type of NaYSnMoO7: Eu3+ phosphor was prepared by the solid-state reaction. Using the Eu3+ ion as a probe, the structural, the micro-structure and the photoluminescence properties of NaYSnMoO7: Eu3+ were studied. The NaYSnMoO7: xEu3+ phosphor exhibited intense red emission at 617 nm under 395 or 466 nm excitation corresponding to the electric dipole (5D0→7F2) transition, which indicated that Eu3+ ions occupied the asymmetric position in the NaYSnMoO7 matrix. The optimal Eu3+-doping concentration was 30 mol% and the concentration quenching mechanism was electrostatic multipole interaction. The Judd-Ofelt (J-O) parameters, the quantum efficiency and gain bandwidth of NaYSnMoO7: 0.30Eu3+ phosphor were calculated. The J-O parameters Ω2＞Ω4 confirmed that the Eu3+ ions occupied asymmetric position in the matrix. The calculated quantum efficiency, the color purity and gain bandwidth were as high as 84%, 92% and 4.90 × 10−27 cm3, respectively. The CIE color coordinates of NaYSnMoO7: 0.30Eu3+ phosphor are closer to the standard red coordinates (0.67, 0.33) than commercial Y2O2S: Eu3+ phosphor (0.622, 0.351). These results suggest that the NaYSnMoO7: Eu3+ phosphors are promising red-emitters for white light-emitting diodes.

Synthesis, structure and optical properties of erbium-doped lithium barium phosphate

Li2BaP2O7 activated with Er3+ ions was prepared by the classic ceramic method and characterized by X-ray diffraction technique, IR, Raman and photoluminescence (PL) spectroscopies. The Li2BaP2O7: Er phosphors exhibited a monoclinic single phase structure with C2/c space group. A green and red emission lines dominate the spectrum upon excitation at 400 nm. The CIE-coordinate (x = 0.308, y = 0.512) were found in green light. Free ion parameters of the Er3+ ions in Li2BaP2O7 and the Judd–Ofelt parameters were calculated and they were used to explore the radiative parameters such as transition probability (AT), and branching ratios (β) related to the Er3+ emission transitions. The calculated 4S3/2 radiative life time around 0.198 ms is compared with the experimental value. The calculated quantum efficiency is about 42%. Li2BaP2O7: Er can be considered as a novel green phosphor.

Structural, absorption and photoluminescence studies of Sm3+ ions doped barium lead alumino fluoro borate glasses for optoelectronic device applications

Samarium ions doped barium lead alumino fluoro borate glasses were prepared by conventional melt quenching technique and characterized by using various spectroscopic techniques. The amorphous nature and functional groups present host glass were confirmed by XRD and FT-IR spectra respectively. From the measured oscillator strengths the Judd-Ofelt (J–O) parameters were evaluated and subsequently used to estimate various radiative properties for the prominent fluorescent levels. The PL spectra show three transitions 4G5/2→6H5/2, 6H7/2, and 6H9/2 at 565 nm, 602 nm and 650 nm in greenish yellow, reddish orange and red regions respectively. The experimental lifetimes correlated with radiative lifetimes to calculate quantum efficiency of the as prepared glasses. The CIE chromaticity coordinates measured establishes reddish orange emission from the as prepared glasses. Based on the emission cross-sections, branching ratios, quantum efficiency and CIE coordinates, it is concluded that the Sm3+ ions doped as prepared glasses are aptly suitable for reddish orange optoelectronics device applications.

Improved visible-light catalytic activities of novel Au/P-doped g-C3N4 photocatalyst for solar fuel production and mechanism

The noble metal decorated photocatalytic materials have received marvelous attention in recent decade owing to their exceptional applications in energy conversion and environmental remediation. Herein, we have successfully fabricated Au decorated phosphorus doped graphitic carbon nitride (Au/P-CN) photocatalyst for the first time via ionic liquid and in situ photo-reduction methods. The resultant photocatalyst exhibits significant visible-light activities for water splitting to evolve H2 and CO2 conversion to CH4. The amount of H2 evolved over Au/P-CN photocatalyst is 97 μmol, ∼12-fold enhanced compared to that of the bare CN (8 μmol). Similarly, the amount of CH4 produced over Au/P-CN photocatalyst is 24 μmol, about 6-fold enhanced compared to that of the bare CN (4 μmol). The calculated quantum efficiencies for H2 evolution and CH4 production are ∼3.60% and ∼2.83%, respectively at λ = 420 nm. The exceptional photocatalytic activities are attributed to the extended visible-light absorption and improved charge carriers separation via the dopant induced surface states and the well decorated Au nanoparticles. This work demonstrate that the Au decorated CN-based photocatalysts show promising applications in photocatalysis for water splitting to evolve H2 and CO2 conversion to CH4 under visible-light irradiation.

Exceptional co-catalyst free photocatalytic activities of B and Fe co-doped SrTiO3 for CO2 conversion and H2 evolution

CO2 should be converted into chemical-fuels, and to reduce H2O to H2 over SrTiO3 (STO) owing to its negative conduction band position vs. NHE. Herein a novel B and Fe co-doped SrTiO3 (B, F-STO) photocatalyst was successfully fabricated via a single-step sol-hydrothermal process. Various experiments confirmed that B and Fe are effectively doped into the STO matrix. Boron substituted oxygen anions, while Fe substituted Ti cations. UV–visible diffuse reflectance spectra (UV–vis DRS) and valence-band X-ray photoelectron spectroscopy (XPS) spectra confirmed that the band gap of STO significantly reduced from 3.4 to 1.9 eV upon co-doping with B and Fe. Hence, the B, F-STO photocatalyst exhibits more absorption (λ ≤ 650 nm) compared to pure STO (λ ≤ 360 nm). Further, from photoluminescence spectra, fluorescence spectra, and photoelectrochemical measurements, charge separation in STO is considerably enhanced by co-doping B and Fe. This resulted in the improved UV–vis light catalytic activities for CO2 conversion to CH4 and CO and H2O splitting to evolve H2. The amounts of CH4 and CO produced over B, F-STO are ∼ 17.2 and 21 μmol, respectively, about 5-fold enhanced compared to that of STO (∼ 3.4 μmol CH4 and 5.2 μmol CO), and the calculated quantum efficiency at λ = 420 nm is ∼ 2.16%. Similarly, the amount of H2 produced over B, F-STO is ∼ 61 μmol, about 6.7-fold enhanced compared to that over STO (9 μmol), and the calculated quantum efficiency at λ = 420 nm is ∼ 2.12%. This work provides feasible routes to fabricate highly efficient SrTiO3-based nanophotocatalysts for solar-fuel production.

Synthesis of S-Doped porous g-C3N4 by using ionic liquids and subsequently coupled with Au-TiO2 for exceptional cocatalyst-free visible-light catalytic activities

The development of new technologies for carbon dioxide reduction, water splitting, and pollutant degradation has been a demanding challenge in the globe due to critical energy and environmental issues. Herein, we have successfully synthesized sulfur doped porous g-C3N4 (S-PCN) using ionic liquid, and then coupled nanocrystalline anatase TiO2 and Au-modified TiO2 to obtain nanocomposites. The amount-optimized 1 Au-6 T/6S-PCN nanocomposite exhibits exceptional visible-light activities for CO2 conversion to CH4, H2 evolution, and 2,4-dichlorophenol degradation, respectively by ∼32-time (365 μmol g−1h−1), ∼41-time (330 μmol g−1h−1) and ∼24-time (95% 10 mg h−1L−1) enhancement compared to the porous g-C3N4 (PCN). The calculated quantum efficiencies for CH4 production and H2 evolution are ∼4.67% and ∼3.34% at 420 nm wavelength. Based on these results, it is suggested that the exceptional photoactivities are attributed to the large surface area (100.5 m2g−1), extended visible-light response and enhanced charge separation via dopant induced surface-states and subsequently coupled Au-TiO2. Furthermore, the CO2 and H as active radicals would be dominant to respectively initiate CO2 and H2O reduction, and the produced OH plays a vital role in 2,4-dichlorophenol degradation. This work demonstrates that the designed PCN-based nanocomposites show promising applications in CO2 photo-reduction, water splitting, and pollutant degradation.

Effect of SU-8 Passivation Layer Induced Stress on the Performance of GaSb Diode

SU-8 was found to be a good candidate for passivation of GaSb diodes, because of its stable chemical properties and high resistivity. However, stresses might be induced during the SU-8 solidification process, which could affect the performance of GaSb diode. Here, we measured the dark currents of devices with different sizes of mesa area and thicknesses of passivation layer, found that the thickness of passivation layer is a key factor for the performance of GaSb based devices. The dark current density of the optimum passivated diode is $9.80\,\,\times \,\, 10^{-6}$ A/cm2 (at −0.3 V bias) and the calculated surface resistivity based on dynamic resistance-area product (R0A) of the passivated diode is $854~\Omega \cdot \text {cm}$ , which are about twentyfold decrease and sixfold increase than that for unpassivated diodes at 77 K, respectively. The calculated quantum efficiency is 36.3% for the passivated device, whereas the value for the unpassivated device is 19.2%.

Sunlight‐Driven Hydrogen Production Using an Annular Flow Photoreactor and g‐C3N4‐Based Catalysts

AbstractSimple modifications of g‐C3N4 (CN) have been studied to maximize hydrogen production under sunlight irradiation conditions. The relatively low surface area CN obtained was subjected to an exfoliation process which 1) increases available catalytic area and 2) modulates the semiconductor charge photohandling. MnOx and metallic Pt, which can act as co‐catalysts, were subsequently added on the surface of exfoliated or bulk counterparts, producing an active material suitable for sunlight applications. The resulting catalysts were fully characterized using a multi‐technique approach. The combination of results indicates that optical properties are strongly defined by the delaminated process whereas the minority phases do not cause physico‐chemical variation of the CN structure. Materials without Pt did not show activity under the investigated reaction conditions. In addition, the collaborative effect of the minority phases on the exfoliated CN was confirmed through a strict quantum efficiency calculation. Stability of the most active sample was similarly examined.

Hollow microspheres consisting of uniform ZnxCd1-xS nanoparticles with noble-metal-free co-catalysts for hydrogen evolution with high quantum efficiency under visible light

Utilizing solar energy in order to produce hydrogen from water is one of the key technologies to deal with energy and environment issues. A photocatalyst with a small band gap, good charge separation, and high stability plays an important role in this process. Recently, zinc cadmium sulfide (ZnxCd1-xS) has caught researchers’ attention due to its unique photocatalytic properties such as the wide range of visible light energy absorption and strong stability during water splitting. Moreover, a unique feature of this semiconductor is the capability of modifying its band gap structure by changing the Zn/Cd ratio. Herein, a series of ZnxCd1-xS solid solutions was synthesized by utilizing metal-glycerate followed by calcination in air and sulfuration under flowing H2S. As a result, a homogeneous hexagonal wurtzite ZnxCd1-xS solid solution could produce hydrogen in a wide range of visible light region. Moreover, using MoS2 as a cocatalyst resulted in the same amount of hydrogen as Pt. The best result was obtained for the Zn30Cd70S solid solution that showed a hydrogen evolution of 12 mmol h−1 g−1 under solar simulator. The calculated quantum efficiencies (QE) in visible light region are: 46.6% at 400 nm to 23.4% at 500 nm as well as 11.3% at 550 nm. There are among the highest QE that have been ever reported for this kind of material under visible light region.

Calculation of Quantum Efficiency of Photodetectors Based on A3B5 Metal-Solid Solutions Contacts

In our investigation, we have modelled the quantum efficiency of the photodetecting structures based on the p-n junction and metal-semiconductor contacts. The calculation has been performed based on the solution of the continuity equation, taking into account the impact of the surface recombination. In most cases, this process has an adverse effect on the parameters of instruments; in particular, in photodetectors, this effect should reduce sensitivity. However, in our investigation it is shown that the effect of the surface recombination may be used as a useful factor for developing selective photodetectors. The effect of the surface recombination process will significantly increase with an increase of the absorption coefficient, since in this case more photons will be absorbed at the surface. Since there is a significant dependence of the absorption coefficient on the incident photon energy in semiconductors, the effect of the surface recombination on the photodetector sensitivity in the long-wave and short-wave regions of the spectral range will be significantly different.

Synthesis of Large Surface‐Area g‐C3N4 Comodified with MnOx and Au‐TiO2 as Efficient Visible‐Light Photocatalysts for Fuel Production

AbstractHerein, this study successfully fabricates porous g‐C3N4‐based nanocomposites by decorating sheet‐like nanostructured MnOx and subsequently coupling Au‐modified nanocrystalline TiO2. It is clearly demonstrated that the as‐prepared amount‐optimized nanocomposite exhibits exceptional visible‐light photocatalytic activities for CO2 conversion to CH4 and for H2 evolution, respectively by ≈28‐time (140 µmol g−1 h−1) and ≈31‐time (313 µmol g−1 h−1) enhancement compared to the widely accepted outstanding g‐C3N4 prepared with urea as the raw material, along with the calculated quantum efficiencies of ≈4.92% and 2.78% at 420 nm wavelength. It is confirmed mainly based on the steady‐state surface photovoltage spectra, transient‐state surface photovoltage responses, fluorescence spectra related to the produced •OH amount, and electrochemical reduction curves that the exceptional photoactivities are comprehensively attributed to the large surface area (85.5 m2 g−1) due to the porous structure, to the greatly enhanced charge separation and to the introduced catalytic functions to the carrier‐related redox reactions by decorating MnOx and coupling Au‐TiO2, respectively, to modulate holes and electrons. Moreover, it is suggested mainly based on the photocatalytic experiments of CO2 reduction with isotope 13CO2 and D2O that the produced •CO2 and •H as active radicals would be dominant to initiate the conversion of CO2 to CH4.

First‐Principles Calculations of Quantum Efficiency for Point Defects in Semiconductors: The Example of Yellow Luminance by GaN: CN+ON and GaN:CN

AbstractPoint defects play an important role in the photoelectrical properties of semiconductor materials, and they can be luminescence centers. However, the relationships among the observed luminescence wavelengths, intensities, and the microscopic processes are in most cases unknown, or depend heavily on parameter fitting. In this work, the light‐emitting quantum efficiencies for point defects using ab initio density functional theory are calculated. The study of radiation recombination for electrons and nonradiation recombination for holes is reported here. The results show that the defect CN transition between “−” and “0” charged levels and the defect CN+ON transition between “0” and “+” charged levels both may be responsible for the yellow luminescence (YL) which is observed in experiment. Moreover, the calculation shows significant thermal quenching of the YL starting at 480 K due to re‐excitation of hole into the valence band from the point defects, which is in relatively good agreement with the experimentally observed value. This work shows that it is possible to use ab initio calculations to understand the microscopic mechanisms and the competitions among different channels for the light emissions caused by defects.

Visible quantum cutting in green-emitting BaF2: Gd3+, Tb3+ phosphor: An approach toward mercury-free lamps

Visible quantum cutting (QC) has been observed in green emitting BaF2 co-doped with Gd3+, Tb3+ phosphor via down-conversion (DC) synthesized by wet chemical method. Powder X-ray diffraction (XRD) analysis shows structural purity of synthesized phosphors. The excitation (PLE) and PL spectra in the vacuum ultraviolet (VUV) or UV region were measured with the help of 4B8-VUV spectroscopy experimental station of the Beijing Synchrotron Radiation Facility (BSRF). In the QC process, one VUV–UV photon absorbed is cut into more than one visible photons emitted by Tb3+ through cross relaxation (CR) and direct energy transfer (DET) between Tb3+ and Tb3+ or Tb3+ and Gd3+, depending on the excitation wavelength. From the emission spectra monitored at different wavelength excitation, the two-step energy transfer process is investigated and theoretically calculated quantum efficiency observed 148% and 177% at the excitation wavelength of 174 nm and 219 nm respectively.