Calculation Of Absorption Cross Sections Research Articles

Crystal growth and spectral properties of a mixed crystal Nd3+:LuYPO4

A new mixed orthophosphate crystal of Nd3+:LuYPO4 was grown by high temperature solution method successfully. The optical properties including polarized absorption and emission spectra as well as the fluorescence decay curve have been investigated in detail. The calculated absorption cross-sections were 18.6 × 10−20 cm2 at 803 nm with a FWHM of 6.10 nm for π-polarization and 8.96 × 10−20 cm2 at 804 nm with a FWHM of 6.07 nm for σ-polarization, respectively. The broad absorption bands wider than those of Nd:YPO4 and Nd:LuPO4 crystals confirm that the incorporation of Lu3+ ions results in a effectively inhomogeneous broadening of the spectra. Based on J-O theory, some typical parameters such as J-O intensity, fluorescence branching rate and radiation lifetime of Nd3+ ions in Nd:LuYPO4 crystal were systematically calculated. Besides, five strong emission peaks located at 1054, 1061, 1066, 1076 and 1081 nm can be observed obviously from fluorescence spectra. All the results show that Nd:LuYPO4 crystal is a promising laser material applied to 1.0 μm with multi-wavelength emission characteristics.

Structure and spectroscopic properties of a disordered Nd:CaGdAl3O7 crystal

A disordered Nd3+-doped CaGdAl3O7 crystal was grown by the optical floating zone method. The absorption and fluorescence spectra of Nd:CaGdAl3O7 crystal were measured, and the spectroscopic properties were studied intensively with the Judd–Ofelt theory. The calculated absorption cross-section was 3.78 × 10-20 cm−2 at 808.5 nm with a full width at half maximum (FWHM) of 19.3 nm. The emission cross-section centered at 1061.6 nm was estimated to be 4.94 × 10-20 cm2 with a FWHM of 12.6 nm, and the fluorescence lifetime of 4F3/2 energy level was measured as 260.7 μs. The experimental results revealed the potential of Nd:CaGdAl3O7 crystal applied in 1.06 μm laser system.

The effect of Y3+ doping upon Nd: S-FAP transparent ceramics for effective spectral performance improvement

In recent years, neodymium (Nd) doped transparent ceramics have played a great role as laser gain media. The ceramics with anisotropic structures have more advantages in luminescence. The Nd, Y co-doped Sr 5 (PO 4 ) 3 F (Nd, Y: S-FAP) nanoparticles were synthesized by a conventional chemical co-precipitation method. The transparent Nd, Y: S-FAP ceramics with high quality were fabricated by the hot-pressed sintering method. Moreover, the Judd-Ofelt (J-O) theory was adopted to further evaluate the spectral properties. The as-synthesized nanoparticles, whose grain size was about 25 nm, were nearly ellipsoidal. The highest transmittance of the ceramic was 2% Nd: S-FAP, reaching 85% at 1000 nm. The calculated absorption cross-section of the 4 I 9/2 → 4 F 5/2 + 2 H 9/2 transition from the measured absorption spectra was 4.58 × 10 −20 cm 2 . With the increase of the concentration of doped Y 3+ ions, the intensity of the emission peak at 1057 nm increased gradually. Moreover, the calculated stimulated emission cross-section of 4 F 3/2 → 4 I 11/2 transitions was 7.61 × 10 −20 cm 2 , which was greatly improved compared to the current matrix. The research, therefore, showed the great promise of Nd, Y: S-FAP as a solid-state laser.

The yellow spectral performances of Dy3+: BaF2 and Dy3+/RE3+(RE3+ = Gd3+, Y3+, Lu3+): BaF2 crystals

2 at.% Dy3+: BaF2 and 2 at.% Dy3+/2 at.% RE3+(RE3+ = Gd3+, Y3+, Lu3+): BaF2 single crystals were grown by the Bridgman-Stockbarger method, and characterized by absorption, visible emission, and fluorescence decay curves. Also, relying on the excitation and emission spectra, decay curves at low temperature (77 K) for Dy3+: BaF2 and Dy3+/RE3+(RE3+ = Gd3+, Y3+, Lu3+): BaF2 crystals have been measured. We found that Dy ions have at least three lattice sites in BaF2 crystal, and the lattice sites of Dy3+ ions can be reduced by co-doping with Gd3+, Y3+ or Lu3+ ions, where Dy3+: BaF2 and Dy3+/RE3+(RE3+ = Gd3+, Y3+, Lu3+): BaF2 single crystals can be considered as quasi-single lattice crystals. From visible fluorescence spectra, it was found that co-doping Gd3+ will increase the emission intensity of yellow light by 20 times, co-doping Y3+ will increase the emission intensity of yellow light by 30 times, and co-doping Lu3+ will increase the emission intensity of yellow light by 25 times. The calculated absorption cross-section, emission cross-section, and fluorescence lifetimes indicate that Dy3+: BaF2 and Dy3+/RE3+(RE3+ = Gd3+, Y3+, Lu3+): BaF2 crystals especially, Dy3+/Y3+: BaF2 crystals are suitable to achieve yellow laser output.

Effect of Material and Shape of Nanoparticles on Hot Carrier Generation

Nonradiative decay of photoexcited plasmons generates energetic nonthermal charge carriers. These hot charge carriers play a major role in plasmonic photocatalysis and photovoltaics. Therefore, establishing the relationship between the hot carrier generation efficiency and the structural and chemical parameters of nanoparticles is crucial for developing highly efficient plasmonic catalysts and photovoltaic materials. In this study, we compare the quantum efficiency of hot carrier generation between gold (AuNPs) and silver nanoparticles (AgNPs), and spherical (AuNSs) and cubic gold nanoparticles (AuNCs). We construct nanoparticle-on-mirror (NPoM) systems where reactant molecules are positioned in the nanogaps between the nanoparticles and gold films. Excitation of the NPoM at 785 nm, followed by the detection of products using surface-enhanced Raman spectroscopy allows us to measure the plasmon-driven reaction yields. Dividing the reaction yield by the calculated absorption cross section at the excitation laser wavelength provides the efficiency of hot carrier generation per absorbed photon. We reveal that AgNPs are more effective at generating hot carriers than AuNPs, which is consistent with the higher electron-surface scattering rate of AgNPs. The hot carrier generation of AuNCs is marginally better than that of AuNSs, which can be attributed to the enhanced electric fields inside the AuNCs in the nanogap region. This study contributes to a rational design of plasmonic catalysts or photovoltaic materials of higher efficiencies.

Erratum to “InGaN Quantum Dot Superlattices as Ratchet Band Solar Cells” [Mar 22 474-482

After publication of the original article [4], we found a unit-conversion error in the calculations of absorption cross sections. None of the equations in the original article are incorrect, but our numerical implementation of the dipole matrix elements of (2) made their calculated values too large by a factor of 25.6. The absorption cross sections $\sigma$ depend on the matrix element squared, so they are all overstated by a factor of 656. The corrected Fig. 4 is changed only in the vertical-axis labels.

Determination of absorption cross-section of RE3+ in upconversion powder materials: Application to β-NaYF4: Er3+

The absorption cross-section of lanthanide ions is essential for the analysis of the lanthanide upconversion system. However, it is difficult to accurately obtain the ion absorption cross-section of luminescence powders. There are some factors that cannot be ignored, such as interface reflection, matrix scattering, and stimulated/spontaneous emission. Therefore, a modified two-flux radiative transfer model is established in our study under the consideration of the absorption, scattering, interface reflection, and stimulated/spontaneous emission effects for lanthanide-doped powder materials. Furthermore, the method to determine the ion absorption cross-section is proposed by measuring the directional-hemispherical reflectance, transmittance, and luminescence lifetime of a specified energy level. The single-doped powders of β-NaYF4: 20% Er3+ and β-NaYF4: 0.05% Er3+ synthesized through a high-temperature solid-state reaction method were selected as the experimental samples and characterized by XRD and SEM. The reflectance, transmittance, and emission spectra of slice samples in the wavelengths of 460 nm–1700 nm were measured. Moreover, the effects of different sample sintering degree, irradiation source powers, and interface conditions on the measured reflectance and the calculated absorption cross-section were investigated. The redshift of the spontaneous emission peaks (4I13/2 and 4I11/2 energy levels) of Er3+ ions in the measurements of reflectance spectra was observed and analyzed. The absorption cross-section of Er3+ ion, the scattering coefficient and interface reflectivities of NaYF4 matrix were determined according to the established model and method. The applicability of the method was experimentally verified. This work provides references for accurate measurements of ion absorption cross-section of lanthanide upconversion luminescence system.

Effect of Nanoparticle Size on Plasmon-Driven Reaction Efficiency.

Hot electron chemistry is of paramount significance because of its applicability to photocatalytic reactions, solar energy conversion, and waste decomposition. The nonradiative decay of excited plasmons in gold nanoparticles (AuNPs) generates highly energetic nonthermal electrons and holes that can induce chemical reactions when transferred to nearby molecules. In this study, we explore the relationship between AuNP size (26-133 nm) and the plasmon-induced reaction yield. To isolate the size from other structural parameters, we prepare perfectly round gold nanospheres (AuNSs) with narrow size distributions. The use of a nanoparticle-on-mirror configuration, in which the reactant molecules (4-mercaptobenzoic acid) are positioned in nanogaps between the AuNSs and a Au film, promotes the generation of hot carriers and allows the highly sensitive detection of the reaction products (benzenethiol) using surface-enhanced Raman spectroscopy. We show that the reaction yield increases as the AuNS size increases up to 94 nm and then decreases for larger AuNSs. This peculiar Λ-shaped size-dependent reactivity can be explained by considering both the plasmonic absorption efficiency of AuNSs and the decay rate of plasmons via electron-surface scattering. The product of the calculated absorption cross section and the inverse of the AuNS size reproduces our experimental results remarkably well. These findings will contribute to the design of highly efficient plasmonic photocatalysts and photovoltaic devices.

Near‐Field Optical Excitations in Silicon Subwavelength Light Funnel Arrays for Broadband Absorption of the Solar Radiation

Broadband absorption is pivotal for the realization of green energy based on solar energy. Decoration of photovoltaic cells with arrays of subwavelength formations provides an efficient means for broadband absorption in thin films. Surface arrays of silicon light funnels (LFs) have been suggested as a promising platform to produce broadband absorption that is considerably superior to other subwavelength arrays such as the well‐known nanopillar (NP) arrays. The current study explores the underlying mechanism of broadband absorption in LF arrays. To this end, the optical near‐field of LF and NP arrays is experimentally probed using a near‐field scanning optical microscopy. It is shown that in LF arrays the near‐field increases as the array period decreases in contrast with NP arrays in which the near‐field decreases with decreasing array period. Also, the experimental near‐field of the arrays follows the numerically calculated absorption cross section of the array‐nested NPs/LFs. Therefore, the origin to the broadband absorption in compact LF arrays is due to field overlap of adjacent LFs which increases the absorption cross section of the individual LFs composing the array. This absorption cross‐sectional enhancement coupled with a higher filling ratio in compact arrays produces broadband absorption that is significantly greater than that of NP arrays.

Spectroscopic investigations on 1.53 μm NIR emission of Er3+ doped multicomponent borosilicate glasses for telecommunication and lasing applications

The multicomponent borosilicate (MBSER) glasses activated with different concentrations of Er3+ ions (varies from 0.1 to 2 mol%) were prepared via conventional melting and rapid quench technique and studied their thermal, structural and spectroscopic characteristics by using DSC, XRD, FTIR, optical absorption, excitation and emission measurements. Judd- Ofelt analysis in correlation with the absorption and emission spectral profiles was performed for the evaluation of several radiative parameters of the as-prepared glasses. Visible and NIR luminescence were recorded at 379 nm excitation and a special consideration is given to 1536 nm emission corresponding to the 4I13/2 → 4I15/2 transition. McCumber theory (MC) is used to determine the stimulated emission cross-section from the calculated absorption cross-section and is found well matched with the emission cross-section obtained from Fuchtbauer-Ladenburg (FL) equation. Better radiative parameters (stimulated emission cross-section (σemi) = 15.78 × 10−21cm2, effective bandwidth (Δλeff) = 67 nm), laser (gain bandwidth (σ(λp) x Δλeff = 1.05 × 10−25 cm3), optical gain (σ(λp) x τR) = 42.5 × 10−25 cm2s)) and gain spectra characteristics suggests the MBSER glasses for optical amplifier and laser applications since they offer a broadened emission spectra in the NIR region.

Radial distribution and absorption cross section of active centers in bismuth-doped phosphosilicate fibers.

Determination of the active centers distribution across the fiber core as well as calculation of absorption cross sections is a challenging task for all types of bismuth-doped fibers. This is due to the low concentration of active centers and the ability of the bismuth ions to form various centers in silica-based glasses. In this work, we demonstrate the results of experimental measurement of radial distribution of bismuth active centers associated with phosphorus in fiber core using the luminescence spectroscopy. The shape of the distribution turned out to have prominent reduction of the active centers in the middle of the core. With these data, absorption cross section spectra were calculated by two methods. Both approaches demonstrated close values of absorption cross sections regardless the bismuth concentration and fiber geometry. The maximum of the absorption cross section was found to be 2.1 ± 0.3 pm2.

Spin polarization of 87Rb atoms with Xe gas and high-pressure buffer gas in a cubic cell

We simulated the optical pumping rate of 87Rb atoms with Xe and high-pressure buffer gas in a cubic cell. We calculated absorption cross-section as a function of pumping laser frequency by considering a pressure and Doppler broadening as gas temperature varies from 364 K to 414 K. In a steady state the spin polarization and the atomic population of 87Rb atoms were obtained by optical pumping in each ground state. We calculated the optimum beam waist, linewidth and detuning of pumping beam to achieve higher population of polarized atoms at cell parameters such as temperature, size. We simulated that the optimum beam waist is 0.3 times of cubic cell length at 250 Torr of di-nitrogen and 50 Torr of Xe gas pressure. The optimum laser beam linewidth parabolically increases with increasing the temperature in range of few ten kelvin and it exponentially decrease with increasing the cubic cell length. We also observed that few ten GHz detuned laser frequency increases the optical pumping rate. These numerical results show appropriate experimental parameter as a function of cell temperature and size to get maximum population of spin polarized atoms in given temperature range.

Physical properties, ligand field and Judd-Ofelt intensity parameters of bio-silicate borotellurite glass system doped with erbium oxide

A glass series containing bio-silicate borotellurite (BSBT) doped with erbium oxide with composition of {[(TeO2)0.8 (B2O3)0.2]0.8 (SiO2)0.2}1-y (Er2O3)y, y = 0.01, 0.02, 0.03, 0.04, 0.05 mol fraction were fabricated using the melt quenching technique. In this glass composition, the bio-silicate was extracted from the rice husk. The X-ray fluorescence (XRF), X-ray diffraction (XRD), molar volume, density, optical absorption and luminescence properties and excitation of the glass sample were investigated. Result of x-ray diffraction (XRD) confirmed the amorphous nature of the glass. The X-ray fluorescence (XRF) verified the achievement of 98.6% of silicate from rice husk. The density is found to be increasing from 3.845 g/cm3 to 4.142 g/cm3 with the increase in the concentration of Er3+. The molar volume is also found to be increasing with concentration of Er3+, but later decreases at 0.04 and 0.05 mol fraction of erbium. The decrease may be due to the tightly packed atom giving rise to a denser glass. The obtained values of the Racah parameters are derived from the absorption spectra region with higher energy. The bonding parameters are found to increase with the increase in the concentration of Er3+ from 0.002789 to 0.002835 while the Racah parameters and nephelauxetic ratio decreased. The increase in crystal field strength also shows a strong field sites. The Judd-Ofelt (J-O) intensity parameters are derived from the UV–Vis spectra and the results showed Ω2 > Ω4 > Ω6 trend with the exception of Erbium at 0.04 mol fraction which showed Ω2 > Ω6 > Ω4 trend. The appearance of higher values of Ω2 and Ω6 indicate the presence of a stronger covalency and lower symmetry around Er3+ ions. MacCumber theory was used to determine the stimulated emission cross section from the calculated absorption cross section for 4I13/2 to 4I15/2 transition. The glass displayed intense green and a week red emission under 380 nm excitation. The width of the gain is found to shift towards the shorter wavelength which proves that this glass system is a good material for photonics and laser applications.

Spectral lines of extreme compact objects

We study the absorption of scalar fields by extreme/exotic compact objects (ECOs) -- horizonless alternatives to black holes -- via a simple model in which dissipative mechanisms are encapsulated in a single parameter. Trapped modes, localized between the ECO core and the potential barrier at the photosphere, generate Breit-Wigner-type spectral lines in the absorption cross section. Absorption is enhanced whenever the wave frequency resonates with a trapped mode, leading to a spectral profile which differs qualitatively from that of a black hole. We introduce a model based on Nariai spacetime, in which properties of the spectral lines are calculated in closed form. We present numerically calculated absorption cross sections and transmission factors for example scenarios, and show how the Nariai model captures the essential features. We argue that, in principle, ECOs can be distinguished from black holes through their absorption spectra.

Qualitative and quantitative analysis of atmospheric methanol using a continuous-wave terahertz spectrometer

We present a specific-window method to subtract the interference of water vapor on terahertz frequency-domain spectroscopy (THz-FDS) at ambient temperature and pressure. A continuous-wave spectrometer based on photomixing was utilized to obtain THz-FDS of methanol vapor in the range of 50–1200 GHz. The distinctly spaced absorption features in the neighborhood of atmospheric windows of transparency were selected to perform linear fitting versus the calculated absorption cross section and obtain the concentration of methanol. Furthermore, the gradually decreased methanol vapor was quantified to demonstrate the reliability of the method.

Photoabsorption cross‐section measurements of 32S, 33S, 34S, and 36S sulfur dioxide from 190 to 220 nm

AbstractThe ultraviolet absorption cross sections of the SO2 isotopologues are essential to understanding the photochemical fractionation of sulfur isotopes in planetary atmospheres. We present measurements of the absorption cross sections of 32SO2, 33SO2, 34SO2, and 36SO2, recorded from 190 to 220 nm at room temperature with a resolution of 0.1 nm (~25 cm−1) made using a dual‐beam photospectrometer. The measured absorption cross sections show an apparent pressure dependence and a newly developed analytical model shows that this is caused by underresolved fine structure. The model made possible the calculation of absorption cross sections at the zero‐pressure limit that can be used to calculate photolysis rates for atmospheric scenarios. The 32SO2, 33SO2, and 34SO2 cross sections improve upon previously published spectra including fine structure and peak widths. This is the first report of absolute absorption cross sections of the 36SO2 isotopologue for the C1B2‐X1A2 band where the amplitude of the vibrational structure is smaller than the other isotopologues throughout the spectrum. Based on the new results, solar UV photodissociation of SO2 produces 34ε, 33Ε, and 36Ε isotopic fractionations of +4.6 ± 11.6‰, +8.8 ± 9.0‰, and −8.8 ± 19.6‰, respectively. From these spectra isotopic effects during photolysis in the Archean atmosphere can be calculated and compared to the Archean sedimentary record. Our results suggest that broadband solar UV photolysis is capable of producing the mass‐independent fractionation observed in the Archean sedimentary record without involving shielding by specific gaseous compounds in the atmosphere including SO2 itself. The estimated magnitude of 33Ε, for example, is close to the maximum Δ33S observed in the geological record.

Strong dipole-quadrupole coupling and Fano resonance in H-like metallic nanostructures.

Under certain conditions of the incident light polarization direction a Fano resonance arises in small gold nanorods arranged in a H-like configuration. This stems from the coupling between a bright dipole plasmon mode excited in the horizontal rod and dark quadrupole plasmon modes in both vertical rods. We investigate these surface plasmon modes, and analyze the dependence of the Fano resonance on the geometry parameters such as rod size and interparticle separation, and refractive index of embedding medium. To describe the degree of this energy transfer, we introduce a new parameter: the Fano resonance efficiency. We calculate absorption cross-sections for visible and NIR spectrum in each element of the structure, and near-field distributions at different wavelengths. We show that Fano resonance in small H-like structures exhibits high sensitivity with respect to the refractive index of the host medium, outperforming the values for larger plasmonic structures based on nanorods already investigated.

Kinetics and mechanism of CH3Br, CHF2Br, and C2HF4Br photolysis in the presence of dioxygen under the action of λ = 253.7 nm light

The photolysis of CH3Br, CHF2Br, and C2HF4Br mixed with oxygen under radiation emitted by a bactericidal mercury lamp (radiation intensity maximum at λ = 253.7 nm) has been investigated. Oxygen was added in order to simulate natural conditions. A photolysis mechanism has been suggested, the corresponding model calculations have been carried out, and the calculated data have been compared with experimental data. The calculated absorption cross sections are in agreement with the literature, thus proving the validity of the mechanism suggested. The ratios between the rate constants of the reactions of the photolytically generated CH3, CHF2, and C2HF4 radicals with molecular bromine and oxygen have been determined.

Nonadiabatic calculations of ultraviolet absorption cross section of sulfur monoxide: isotopic effects on the photodissociation reaction.

Ultraviolet absorption cross sections of the main and substituted sulfur monoxide (SO) isotopologues were calculated using R-Matrix expansion technique. Energies, transition dipole moments, and nonadiabatic coupling matrix elements were calculated at MRCI/AV6Z level. The calculated absorption cross section of (32)S(16)O was compared with experimental spectrum; the spectral feature and the absolute value of photoabsorption cross sections are in good agreement. Our calculation predicts a long lived photoexcited SO* species which causes large non-mass dependent isotopic effects depending on the excitation energy in the ultraviolet region.

Ag nanoparticles enhanced 2 um luminescences of Ho3+/Tm3+ codoped bismuth germanate glasses

The Ho3+/Tm3+ codoped bismuth germanate glasses containing Ag nanoparticles (NPs) are synthesized by a chemical reduction method based on the conventional melting-quenching technique. The effect of concentration of Ag NPs on the 2 um emission is studied. The absorption band related to the surface plasmon resonance (SPR) of the Ag NPs is located in a range from 500 to 900 nm. Transmission electron microscopic image clearly reveals homogeneously dispersed Ag NPs with the sizes ranging from 5 to 10 nm. The luminescence spectra in a range of 1.7-2.3 um are collected. With the addition mass fraction of the AgCl up to 0.3%, the intensity of emission band of Ho3+ ions, centered at 2.03 um, is increased by 10 folds. The enhancement of 2 um luminescence is attributed to the enhanced local field induced by SPR of Ag NPs. The calculated absorption cross section and emission cross section are 0.491 10-20 cm-2 and 1.0310-20 cm-2, respectively. When the gain coefficient p=0.2, the positive gain would be realised.