Energy transfer rate and electron–phonon coupling properties in Eu3+‐doped nanophosphors

A series of controllable emissions SrWO₄:Eu³⁺ and charge‐compensated SrWO₄: (m = 0.01 or 0.20) phosphors was successfully prepared via a simple co‐precipitation method. The energy transfer mechanism was studied based on the Huang's theory. A low magnitude of Huang‐Rhys factor (10^?2) was calculated using phonon sideband spectra. The Judd–Ofelt parameters Ω_λ (λ = 2, 4 and 6) of Eu³⁺‐activated SrWO₄ doped with charge compensation were obtained. The calculated Commission Internationale de l'Eclairage chromaticity coordinates were found to be about (0.67, 0.33) for SrWO₄: and charge‐compensated SrWO₄: phosphors, which coincided with the National Television Standard Committee system standard values for red. A white light emission was obtained under 362 nm excitation. The correlated color temperature was computed by a simple equation to characterize light sources. Thus, warm white light‐emitting diodes with higher Ra can be constructed by combining as‐prepared high efficiency, low correlated color temperature and high color purity phosphor.     

Emission analysis of RE3+ (RE = Sm,Dy):B2O3‐TeO2‐Li2O‐AlF3 glasses

This article reports on the optical properties of 0.5% mol of Sm³⁺, Dy³⁺ ion‐doped B₂O₃‐TeO₂‐Li₂O‐AlF₃ (LiAlFBT) glasses. The glass samples were characterized by optical absorption and emission spectra. Judd‐Ofelt theory was applied to analyze the optical absorption spectra and calculate the intensity parameters and radiative properties of the emission transitions. The emission spectra of Sm³⁺ and Dy³⁺:LiAlFBT glasses showed a bright reddish‐orange emission at 598 nm (⁴G_5/2 → ⁶H_7/2) and an intense yellow emission at 574 nm (⁴F_9/2 → ⁶H_13/2), respectively. Full width at half maximum (FWHM), stimulated emission cross section, gain bandwidth and optical gain values were also calculated to extend the applications of the Sm³⁺ and Dy³⁺:LiAlFBT glasses. Copyright © 2012 John Wiley & Sons, Ltd.     

Spectral‐converting study of Ba9–3(m+n)/2ErmYbnY2Si6O24 (m = 0.005 – 0.2, n = 0 – 0.3) orthosilicate phosphors

Optical materials composed of Ba_9–3(m+n)/2Er_mYb_nY₂Si₆O₂₄ (m = 0.005–0.2, n = 0–0.3) were prepared using a solid‐state reaction. The X‐ray diffraction patterns of the obtained phosphors were examined to index the peak positions. The photoluminescence (PL) excitation and emission spectra of the Er³⁺‐activated phosphors and the critical emission quenching as a function of Er³⁺ content in the Ba_9–3m/2Er_mY₂Si₆O₂₄ structure were monitored. The spectral conversion properties of Er³⁺ and Er³⁺–Yb³⁺ ions doped in Ba₉Y₂Si₆O₂₄ phosphors were elucidated under diode‐laser irradiation at 980 nm. Up‐conversion emission spectra and the dependence of the emission intensity on pump power for the Ba_8.55Er_0.1Yb_0.2Y₂Si₆O₂₄ phosphor were investigated. The desired up‐conversion of the emitted light, which passed through the green, yellow, orange and red regions of the spectrum, was achieved through the use of appropriate Er³⁺ and/or Yb³⁺ concentrations in the host structure and 980 nm excitation light. The up‐conversion mechanism in the phosphors is described by an energy‐level schematic. Copyright © 2015 John Wiley & Sons, Ltd.     

Fluorimetric determination of febuxostat in dosage forms and in real human plasma via Förster resonance energy transfer

A rapid, simple, selective and precise fluorimetric method was developed and validated for determination of a selective xanthine oxidase inhibitor; febuxostat (FBX) in pharmaceutical formulations and in human plasma. The proposed method is based on quenching effect of FBX on the fluorescence intensity of terbium (Tb³⁺) through fluorescence resonance energy transfer (FRET) from Tb³⁺ to FBX. The formed complex was measured at λ_ex. 320 nm/λ_em. 490 nm against a reagent blank. Fluorescence intensity of Tb³⁺ was diminished when FBX was added. A linear relationship between the fluorescence quenching value of the formed complex and the concentration of FBX was investigated. The reaction conditions and the fluorescence spectral properties of the complex have been studied. The linearity range of the developed method was 1.0–16.0 μg/ml. The suggested method was applied successfully for the estimation of FBX in bulk powder, dosage forms and spiked plasma samples with excellent recoveries (96.79–98.89%). In addition, the developed method has been successfully applied for determination of FBX in real plasma samples collected from healthy volunteers with good recoveries (82.06–85.65%). All obtained results of the developed method were statistically analyzed and validated according to ICH (International Conference on Harmonization) guidelines.     

Low temperature-synthesized MgAl2O4:Eu3+ nanophosphors and their structural validations using density functional theory: photoluminescence,photocatalytic, and electrochemical properties for multifunctional applications

A low temperature-assisted and oxalyl dihydrazide fuel-induced combustion synthesized series of uncalcined MgAl₂O₄:Eu³⁺ nanophosphors showed an average crystallite size of ~20 nm, and bandgap energy (E_g) of 4.50–5.15 eV, and were validated using density functional theory and found to match closely with the experimental values. The photoluminescence characteristic emission peaks of Eu³⁺ ions were recorded between 480 and 680 nm. The nanophosphors excited at 392 nm showed f–f transitions assigned as ⁵D₀→⁷F_J (J = 0, 1, 2, and 3). The optimized MgAl₂O₄ phosphors had Commission Internationale de l'Eclairage coordinates in the red region, a correlated colour temperature of 2060 K, and a colour purity of 98.83%. The estimated luminescence quantum efficiency ( $\eta$) was observed to be ~63% using Judd–Ofelt analysis. Electrochemical and photocatalytic performance were explored and indicated its multifunctional applications. Therefore, MgAl₂O₄:Eu³⁺ nanophosphors could be used for the fabrication of light-emitting diodes, industrial dye degradation, and as electrodes for supercapacitor applications.     

Emission analysis of Tb3+‐and Sm3+‐ion‐doped (Li2O/Na2O/K2O) and (Li2O + Na2O/Li2O + K2O/K2O + Na2O)‐modified borosilicate glasses

Four series of borosilicate glasses modified by alkali oxides and doped with Tb³⁺ and Sm³⁺ ions were prepared using the conventional melt quenching technique, with the chemical composition 74.5B₂O₃ + 10SiO₂ + 5MgO + R + 0.5(Tb₂O₃/Sm₂O₃) [where R = 10(Li₂O /Na₂O/K₂O) for series A and C, and R = 5(Li₂O + Na₂O/Li₂O + K₂O/K₂O + Na₂O) for series B and D]. The X‐ray diffraction (XRD) patterns of all the prepared glasses indicate their amorphous nature. The spectroscopic properties of the prepared glasses were studied by optical absorption analysis, photoluminescence excitation (PLE) and photoluminescence (PL) analysis. A green emission corresponding to the ⁵D₄ → ⁷F₅ (543 nm) transition of the Tb³⁺ ions was registered under excitation at 379 nm for series A and B glasses. The emission spectra of the Sm³⁺ ions with the series C and D glasses showed strong reddish‐orange emission at 600 nm (⁴G_5/2 →⁶H_7/2) with an excitation wavelength λ_exci = 404 nm (⁶H_5/2→⁴F_7/2). Furthermore, the change in the luminescence intensity with the addition of an alkali oxide and combinations of these alkali oxides to borosilicate glasses doped with Tb³⁺ and Sm³⁺ ions was studied to optimize the potential alkali‐oxide‐modified borosilicate glass.     

Free radical scavenging activity of novel thiazolidine‐2,4‐dione derivatives

Free radical activity towards superoxide anion radical (), hydroxyl radical (HO^?) and 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH^?) of a series of novel thiazolidine‐2,4‐dione derivatives (TSs) was examined using chemiluminescence, electron paramagnetic resonance (EPR) and EPR spin trapping techniques. 5,5‐Dimethyl‐1‐pyrroline‐N‐oxide (DMPO) was applied as the spin trap. Superoxide radical was produced in the potassium superoxide/18‐crown‐6 ether dissolved in dimethyl sulfoxide. Hydroxyl radical was generated in the Fenton reaction (Fe(II) + H₂O₂. It was found that TSs showed a slight scavenging effect (15–38% reduction at 2.5 mmol/L concentration) of the DPPH radical and a high scavenging effect of (41–88%). The tested compounds showed inhibition of HO^? ‐dependent DMPO‐OH spin adduct formation (the amplitude of EPR signal decrease ranged from 20 to 76% at 2.5 mmol/L concentration. Our findings present new group compounds of relatively high reactivity towards free radicals. Copyright © 2012 John Wiley & Sons, Ltd.     

The structure and luminescence properties of Mn2+/Eu2+/Er3+‐doped MgO‐Ga2O3‐SiO2 glasses and glass‐ceramics

The MgO–Ga₂O₃–SiO₂ glasses and glass‐ceramics samples doped with Eu²⁺/Mn²⁺/Er³⁺ and heated in reductive atmosphere were prepared by the sol–gel method. The structure, morphology and the luminescence properties were studied using X‐ray diffraction, high‐resolution transmission electron microscope, fluorescence spectra, and up‐conversion emission. The luminescence characteristics of doped ions could be influenced by temperature and matrix component. The characteristic emission of Mn²⁺, Eu²⁺ and Er³⁺ were seen and the energy transfer efficiency from Eu²⁺ to Mn²⁺ was enhanced as Mn²⁺ concentration was increased. In addition, the two‐photon process was determined for the Er³⁺‐doped samples.     

Effect of erbium ion concentration on structural and luminescence properties of lead borosilicate glasses for fiber amplifiers

This investigation reports, the effect of the concentration of erbium and lead ions on the physical, structural and optical properties of lead borosilicate glasses. These glasses were synthesized by the melt quench method. In the synthesis, the concentration of the erbium (Er³⁺) ion was varied in the order of 0.0, 0.1, 0.5, 1.0 and 2.0 mol% and lead (Pb²⁺) ion was varied in the order of 30, 29.9, 29.5, 29 and 28 mol%. The glasses were analyzed using X‐ray diffraction (XRD), Fourier transform infrared (FT‐IR) and UV–vis–NIR spectroscopy. From XRD, the amorphous nature of lead borosilicate glasses was confirmed. The functional groups which were present in the glasses have been identified by analyzing the FT‐IR spectrum. From the absorption spectra, the oscillator strengths as well as the Judd–Ofelt (JO) intensity parameters were determined and compared with other hosts. The JO intensity parameters were further used to calculate certain radiative properties for the excited luminescent levels of Er³⁺ ion. From emission spectra, full width at half maxima (FWHM), stimulated emission cross‐sections (σ_e) and certain lasing parameters were evaluated and compared with reference host glasses. The lifetimes of ⁴I_13/2 excited level of Er³⁺ ion have also been recorded and analyzed. The calculated and experimental lifetimes were compared in terms of quantum efficiencies. From the photoluminescence analysis, the erbium doped lead borosilicate glasses well suited for optical fiber amplifiers are discussed.     

Studies on the antioxidant activities of some new chromone compounds

Recent reviews evidence that the naturally occurring compounds containing the chromone skeleton exhibit antiradical activities, providing protection against oxidative stress. The antioxidant activities of 13 new synthesized chromonyl‐2,4‐thiazolidinediones, chromonyl‐2,4‐imidazolidinediones and chromonyl‐2‐thioxoimidzolidine‐4‐ones were evaluated using in vitro antioxidant assays, including superoxide anion radical (), hydroxyl radical (), 2,2‐diphenyl‐1‐picryl‐hydrazyl free radical (DPPH^?) scavenging capacity and total antioxidant capacity ferric ion reducing activity. Superoxide anion radical was produced using potassium superoxide/18‐crown‐6‐ether dissolved in dimethylsulfoxide, and the Fenton‐like reaction (Fe(II) + H₂O₂) was a generator of hydroxyl radicals. Chemiluminescence, spectrophotometry, electron paramagnetic resonance (EPR) and 5,5‐dimethyl‐1‐pyrroline‐N‐oxide (DMPO) as the spin trap were the measurement techniques. The results showed that the majority of the chromone derivatives tested showed a strong scavenging effect towards free radicals, similar to the chemiluminescence reaction with superoxide anion radical with a high activity, inhibition of the DMPO‐OOH radical EPR signal (24–58%), the DMPO‐OH radical EPR signal (4–75%) and DPPH radical EPR signal (6–100%) at 1 mmol/L. Several of the examined compounds exhibited the high reduction potentials. The results obtained show that the new synthesized chromone derivatives may directly scavenger reactive oxygen species and thus may play a protective role against oxidative damage. Copyright © 2014 John Wiley & Sons, Ltd.     

Optical analysis of RE3+ (RE = Pr3+, Er3+ and Nd3+):cadmium lead boro tellurite glasses

This article reports on the optical characterization of Pr³⁺‐, Er³⁺‐ and Nd³⁺‐doped cadmium lead boro tellurite (CLBT) glasses prepared using the melt quenching method. The visible–near infrared (Vis–NIR) absorption spectra of these glasses were analyzed systematically. On measuring the NIR emission spectra of Er³⁺:CLBT glasses, a broad emission band centered at 1536 nm (⁴I_13/2 → ⁴I_15/2) was observed, as were three NIR emission bands at 900 nm (⁴F_3/2 → ⁴I_9/2), 1069 nm (⁴F_3/2 → ⁴I_11/2) and 1338 nm (⁴F_3/2 → ⁴I_13/2) from Nd³⁺:CLBT glasses and an NIR emission band at 1334 nm (¹G₄ → ³H₅) from Pr³⁺:CLBT glasses at an excitation wavelength (λ_ex) of 514.5 nm (Ar⁺ laser). Copyright © 2016 John Wiley & Sons, Ltd.     

Impact of Hydroxylation and Hydration on the Reactivity of α‐Fe2O3 (0001) and (102) Surfaces under Environmental and Electrochemical Conditions

Hematite (α‐Fe₂O₃) is widely used as a catalytic electrode material in photo‐electrochemical water oxidation, where its surface compositions and stabilities can strongly impact the redox reaction process. Here, its surface configurations in environmental or electrochemical conditions are assessed via density functional theory (DFT) calculations conducted at the Perdew, Burke, and Ernzerhof (PBE)+U level. The most energetically favorable surface domains of α‐Fe₂O₃ (0001) and (102) are predicted by constructing the surface phase diagrams in the framework of first‐principle thermodynamics. The relative surface stabilities are investigated as a function of partial pressures of oxygen and water, temperature, solution pH, and electrode potential not only for perfect bulk terminations but also for defect‐containing surfaces having various degrees of hydroxylation and hydration. In order to assess the impact on the redox reactions of the surface planes as well as of the extent of surface hydration/hydroxylation, the thermodynamics of the four‐step oxygen evolution reaction (OER) mechanism are examined in detail for different models of the α‐Fe₂O₃ (0001) and (102) surfaces. Importantly, the results underline that the nature of the surface termination and the degree of near‐surface hydroxylation give rise to significant variations in the OER overpotentials.     

Optical analysis of RE3+ (RE = Nd or Er):B2O3–P2O5–CaF2–ZnO–(Li2O/Na2O/K2O) glasses

Calcium boro fluoro zinc phosphate glasses modified using alkali oxide and doped with Nd³⁺ and Er³⁺ ions with the chemical composition of 69.5 (B₂O₃) + 10 (P₂O₅) + 10 (CaF₂) + 5 (ZnO) + 5 (Na₂O/Li₂O/K₂O) + 0.5 (Er₂O₃/Nd₂O₃) were prepared using a conventional melt quenching technique. The results of X-ray diffraction patterns indicated the amorphous nature of all the prepared glasses. The visible–near-infrared red (NIR) absorption spectra of these glasses were analyzed systematically. The NIR emission spectra of Er³⁺ and Nd³⁺:calcium boro fluoro zinc phosphate glasses showed prominent emission bands at 1536 nm (⁴I_13/2→⁴I_15/2) and 1069 nm (⁴F_3/2→⁴I_11/2) respectively with λ_exci = 514.5 nm (Ar⁺ laser) as the excitation source.     

Influence of Er3+ concentration on the photoluminescence characteristics and excitation mechanism of Gd2O3:Er3+ phosphor synthesized via a solid‐state reaction method

An Er³⁺‐doped phosphor of Gd₂O₃ (Gd₂O₃:Er³⁺) was prepared using a conventional solid‐state reaction method. The structure and particle size were determined from X‐ray powder diffraction measurements. The average particle size of the phosphor was in between 20 and 50 nm. The particle size and structure of the phosphor were further confirmed by transmission electron microscopy (TEM) analysis. Luminescence spectra were recorded under excitation wavelengths of 275, 380, 515 and 980 nm. The visible upconversion and downconversion luminescence spectra of the Gd₂O₃:Er³⁺ phosphor were investigated as a function of Er³⁺ ion concentration. The upconverted emission at 980 nm excitation shows enhanced red emission with respect to green emission as the dopant concentration increased. Similar results were observed for downconversion emission under 275 and 380 nm excitation wavelengths. The mechanisms responsible for populating the ⁴S_3/2 and ⁴ F_9/2 levels, for green and red emissions, respectively, are different for different excitations and for different concentrations of Er³⁺. Copyright © 2014 John Wiley & Sons, Ltd.     

The effect of O2 and pressure on thiosulfate oxidation by Thiomicrospira thermophila

Microbial sulfur cycling in marine sediments often occurs in environments characterized by transient chemical gradients that affect both the availability of nutrients and the activity of microbes. High turnover rates of intermediate valence sulfur compounds and the intermittent availability of oxygen in these systems greatly impact the activity of sulfur‐oxidizing micro‐organisms in particular. In this study, the thiosulfate‐oxidizing hydrothermal vent bacterium Thiomicrospira thermophila strain EPR85 was grown in continuous culture at a range of dissolved oxygen concentrations (0.04–1.9 mM) and high pressure (5–10 MPa) in medium buffered at pH 8. Thiosulfate oxidation under these conditions produced tetrathionate, sulfate, and elemental sulfur, in contrast to previous closed‐system experiments at ambient pressure during which thiosulfate was quantitatively oxidized to sulfate. The maximum observed specific growth rate at 5 MPa pressure under unlimited O₂ was 0.25 hr^?1. This is comparable to the μ_max (0.28 hr^?1) observed at low pH (<6) at ambient pressure when T. thermophila produces the same mix of sulfur species. The half‐saturation constant for O₂ () estimated from this study was 0.2 mM (at a cell density of 10⁵ cells/ml) and was robust at all pressures tested (0.4–10 MPa), consistent with piezotolerant behavior of this strain. The cell‐specific was determined to be 1.5 pmol O₂/cell. The concentrations of products formed were correlated with oxygen availability, with tetrathionate production in excess of sulfate production at all pressure conditions tested. This study provides evidence for transient sulfur storage during times when substrate concentration exceeds cell‐specific and subsequent consumption when oxygen dropped below that threshold. These results may be common among sulfur oxidizers in a variety of environments (e.g., deep marine sediments to photosynthetic microbial mats).     

Photoluminescence properties of rare‐earth‐doped (Er3+,Yb3+) Y2O3 nanophosphors by a combustion synthesis method

In this work, we report the synthesis of Y₂O₃:Er³⁺, Y₂O₃:Yb³⁺ and Y₂O₃:Er³⁺,Yb³⁺ nanophosphors by the combustion synthesis method using urea as fuel. The doping agents were incorporated in the form of erbium nitrate and ytterbium nitrate. X‐Ray diffraction (XRD) patterns revealed that the synthesized particles have a body‐centered cubic structure with space group Ia‐3. The photoluminescence (PL) properties were investigated after UV and infrared irradiation at room temperature. A strong characteristic emission of Er³⁺ and Yb³⁺ ions was identified, and the influence of doping concentration on the PL properties was systematically studied. Energy transfer from Yb³⁺ to Er³⁺ ions was observed in Y₂O₃ nanophosphors. The obtained result may be useful in potential applications such as bioimaging. Copyright © 2015 John Wiley & Sons, Ltd.     

Erbium(III) ion-doped borate-based glasses for 1.53 μm broad band applications

Novel erbium(III) ion-doped borate-based glasses (Er³⁺:BCNF) by conventional melt-quenching technique were designed and synthesized. The glasses were characterized for their structural, vibrational and spectroscopic properties. The nephelauxetic ratio, bonding parameters, and Judd–Ofelt (JO) intensity parameters (Ω_λ λ = 2, 4 and 6) were determined by using absorption spectrum of 1 mol% Er₂O₃ doped glass. These JO parameters were utilized to derive radiative properties for various excited states of erbium(III) ions. Emission cross-section for ⁴I_13/2 → ⁴I_15/2 transition of erbium(III) ions was computed through McCumber theory. The decay curves for (²H_11/2, ⁴S_3/2) and ⁴I_13/2 levels were recorded and analysed. All the results of Er³⁺:BCNF glasses revealed that the studied glasses are efficient and thermally stable and could be suitable for display devices, optical amplification and green laser applications.     

Amplification of blue emission of Tm3+ ions in Li2O-HfO2-SiO2 glass system by means of Au0 metallic particles

Li₂O-HfO₂-SiO₂-Tm₂O₃:Au₂O₃ glass samples (containing fixed content of Tm₂O₃ and different concentration of Au₂O₃) were prepared and characterized. Bearing of Au⁰ metallic particles (MPs) on improving blue emission of thulium ions (Tm³⁺) ions was explored. Optical absorption (OA) spectra exhibited multiple bands excited from ³H₆ of Tm³⁺. Additionally, a broad peak in the wavelength range 500–600 nm due to surface plasmon resonance (SPR) of Au⁰ MPs was noticed in the spectra. Photoluminescence (PL) spectra (of thulium free glasses) indicated a peak in the visible range due to sp → d electronic transition of Au⁰ MPs. Luminescence spectra of Tm³⁺ and Au₂O₃ co-doped glasses exhibited intense blue emission with substantial increase of intensity with increase of Au₂O₃ content. Bearing of Au⁰ MPs on the reinforcement of blue emission of Tm³⁺ was discussed in detail with kinetic rate equations.     

Structural,optical, and luminescence properties of Dy3+-activated potassium calcium silicate phosphor for white light-emitting diodes

A dysprosium (Dy³⁺)-activated potassium calcium silicate (K₄CaSi₃O₉) phosphor was prepared using a solid-state synthesis route. The phosphor had a cubic structure with the space group Pa $\overline{3}$ as confirmed using X-ray diffraction (XRD) measurements. Details of surface morphology and elemental composition of the as-synthesized undoped KCS phosphor was obtained using scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) spectroscopy. The chemical structure as well as the vibrational modes present in the as-prepared KCS phosphor was analyzed using Fourier transform infrared (FT-IR) spectroscopy. Diffuse reflectance spectra (DRS) were used to determine the optical bandgap of the phosphors and were found to be in the optical range 3.52–3.71 eV. Photoluminescence (PL) spectra showed intense yellow emission corresponding to the ⁴F_9/2→⁶H_13/2 transition under 350 nm excitation. Commission International de l′Eclairage colour chromaticity coordinates were evaluated using the PL spectral data lie within the white region. Dexter theory and the Inokuti–Hirayama (I–H) model were applied to study the nature of the energy transfer mechanism in the as-prepared phosphors. The relatively high activation energy of the phosphors was evaluated using temperature-dependent PL (TDPL) data and confirmed the high thermal stability of the titled phosphor. The abovementioned results indicated that the as-prepared KCS:Dy³⁺ phosphor was a promising candidate for n-UV-based white light-emitting diodes.     

Synthesis,characterization and thermoluminescence studies of (ZnS)1‐x(MnTe)x nanophosphors

The present paper reports the thermoluminescence (TL) of (ZnS)_1‐x(MnTe)_x nanophosphors that were prepared by a wet chemical synthesis method. The structure investigated by X‐ray diffraction patterns confirms the formation of a sphalerite phase whose space group was found to be F 3m. From XRD, TEM and SEM analyses the average sizes of the particles were found to be 12 nm, 11 nm and 15 nm, respectively. Initially the TL intensity increased with increasing values of x because the number of luminescence centres increased; however, for higher values of x the TL intensity decreased because of the concentration quenching. Thus the TL, mechanoluminescence and photoluminescence intensities are optimum for a particular value of x, that is for x = 0.05. Thermoluminescence of the (ZnS)_1‐x (MnTe)_x nanophosphor has not been reported previously. There were two peaks seen in the thermoluminescence glow curves in which the first peak lay at 105–100 °C and the second peak lay at 183.5–178.5 °C. The activation energies for the first and second peaks were found to be 0.45 eV and 0.75 eV, respectively.