Spontaneous Emission Coefficients Research Articles

Theoretical study of the spectroscopy and radiative transition probabilities of Si2 from visible to infrared.

High level ab initio calculations on the electronic states of a silicon dimer (Si2) have been carried out by employing a multi-reference configuration interaction plus Davidson correction (MRCI + Q) approach with the aug-cc-pVQZ basis set. The scalar relativistic correction is taken into consideration by the second-order Douglas-Kroll-Hess approximation. In the present work, the transition properties (oscillator strength, Einstein spontaneous emission coefficient and radiative lifetime) of the singlet-singlet, triplet-triplet, and quintet-quintet transitions of Si2 are discussed. We emphasize the triplet-triplet emission bands H3Σ-u-X3Σ-g, K3Σ-u-X3Σ-g and D3Πu-L3Πg which are dominant for 0-11 (18 822 cm-1), 0-0 (30 672 cm-1), and 0-0 (28 881 cm-1) transitions, respectively. In addition, the strong experimentally observed b1Πu-d1Σ+g band around 4184 cm-1 corresponds to the second 1Σ+g-b1Πu combination in the infrared region. The calculated oscillator strengths of the singlet-singlet transitions (f1Πg-e1Σ-u, 21Πg-b1Πu, b1Πu-d1Σ+g and g1Δu-a1Δg) are in the order of 10-3. From a theoretical point of view, the 0-0 sub-band for the f1Πg-e1Σ-u transition, 0-7 for 21Πg-b1Πu, 0-0 for b1Πu-d1Σ+g and the 0-7 vibronic bands for the g1Δu-a1Δg transition may be observed experimentally. It is expected that the present results could provide theoretical support for a deeper understanding of the experimental Si2 spectra providing further applications in astrophysics.

Learning to measure infrared properties of street views from visible images

With the rapid development of infrared cameras, infrared images which have the unique advantage of all-weather detection ability are more and more incorporated into practical applications. However, it is hard to develop infrared-domain artificial intelligence with the shortage of labeled infrared data. Traditional infrared image simulation techniques face the problem of strict parameters, slow solution speed, and limited scenarios. In this paper, we tackle the problem of simulating infrared image proprieties with generative networks via reference to visible images. We propose a novel infrared image generation model that complied with the infrared imaging principle, the V2IR-GAN, consisting of spontaneous emission, reflected radiation and transmission coefficient modules. Extensive experiments and analyses are conducted to demonstrate the high stimulative performance of the V2IR-GAN, showing that it achieves the best SSIM of 88.2% against the state-of-the-art generative models. We also provide a specific application to validate the practicability of the V2IR-GAN.

Microscopic morphology independence in linear absorption cross-section of CsPbBr3 nanocrystals

Multiple morphologies of colloidal perovskite nanocrystals (NCs) diversify their optical and electronic properties. Among them, the linear absorption cross-section (σ) is a primary parameter to determine their intrinsic photophysical features, and consequently, application potential. Herein, three morphologies of all-inorganic hybrid colloidal perovskite CsPbBr3 NCs, nanocubes (NBs), nanoplatelets (NLs), and nanowires (NWs), were targeted, and their linear σ values were obtained through femtosecond transient absorption (TA) spectroscopy analysis. At high excitation energy well above the bandgap, the σ per particle of all CsPbBr3 NCs linearly increased with the particle volume (VNC) regardless of the morphology with the value of σ400 = 9.45 × 104 cm−1 × VNC (cm2). Density functional theory (DFT) calculation confirmed the negligible influence of shapes on the optical selection rules. The Einstein spontaneous emission coefficients calculated from the σ values define the intrinsic radiative recombination rate. However, reduced size dependence is observed when the excitation energy is close to the bandgap (i.e., at 460 nm) with the value of σ460 = 2.82 × 108 cm0.65 × (VNC)0.45 (cm2). This should be ascribed to the discrete energy levels as well as lower density of states close to the band edge for perovskite NCs. These results provide in-depth insight into the optical characteristics for perovskite NCs.

The Spectroscopic Atomic and Molecular Databases at the Paris Observatory

This paper is intended to give a comprehensive overview of the current status and developments of the Paris Observatory STARK-B, MOLAT and SESAM databases which can be interrogated thanks to interoperability tools. The STARK-B database provides shifting and broadening parameters of different atomic and ionic transitions due to impacts with charged particles (the so-called Stark broadening) for different temperatures and densities. The spectroscopic MOLAT and SESAM databases provide the wavelengths, the oscillator strengths or Einstein spontaneous emission coefficients of H 2 , CO and isotopologues molecules.

Thermodynamic stability and spectroscopic properties of alkaline earth monobromides: The cases of MgBr2+ and BaBr2+

The low-lying electronic states of the dications MgBr2+ and BaBr2+ are investigated at a high level of theory. Potential energy curves are constructed, and the associated spectroscopic parameters determined. BaBr2+ is thermodynamic stable and MgBr2+ metastable. The state X 2Π of BaBr2+ is bound (De) by 22.60 kcal mol−1, with (Re, ωe) equal to (6.146 a0, 123.9 cm−1). The state A 2Σ+ lies higher by 5049 cm−1 with De = 8.43 kcal mol−1, ωe = 86.9 cm−1. For the dication MgBr2+, the state X 2Π has a deep well with an effective De (barrier height) of 51.18 kcal mol−1, Re = 4.500 a0, and ωe = 308.3 cm−1. The first excited state (A 2Σ+) lies higher by 12,091 cm−1 with De = 26.48 kcal mol−1, ωe = 236.6 cm−1. Einstein spontaneous emission coefficients (Av́v́́) are reported, and lifetimes estimated. New experimental results for the mass spectra of MgBr2+ are also provided.

Thermodynamic stability of diatomic dications of the families of alkaline earth oxides and hydrides: The cases of BaO2+ and BaH2+

The low-lying electronic states of the diatomic dications BaO2+ and BaH2+ are investigated at a high level of theory. The potential energy curves constructed and the associated spectroscopic parameters provide a global and reliable characterization of these species attesting for their thermodynamic stability. The ground state (X 3Σ−) of BaO2+ is bound (De) by 13.11 kcal mol−1, with an equilibrium distance of 5.526 a0, and the harmonic constant (ωe) equal to 175.1 cm−1. The first excited state (A 3Π), lying higher by 3216 cm−1, is also thermodynamic stable (De = 4.04 kcal mol−1, ωe = 123.7 cm−1). Einstein spontaneous emission coefficients (Av′v″) were evaluated for all band systems, and lifetimes estimated. For the dication BaH2+, only the ground state (X 2Σ+) is thermodynamic stable with De = 5.50 kcal mol−1, Re = 5.444 a0, and ωe = 409.4 cm−1. New experimental results for the mass spectra of BaO2+ are also provided.

Strain and built-in potential effects on optical properties of wurtzite GaN/AlInN quantum dots

Light emission characteristics of wurtzite (WZ) GaN/AlxIn1−xN quantum dots (QDs) with piezoelectric (PZ) and spontaneous (SP) polarizations were investigated as a function of Al content through self-consistent calculations. The spontaneous emission coefficient rapidly increases with decreasing Al content and becomes a maximum at about x = 0.8. This is mainly attributed to the fact that the overlap integral between electron and hole wavefunctions is enhanced owing to the broadened potential shape from strain and built-in potential in the valence band. On the other hand, GaN/AlxIn1−xN quantum wells (QWs) shows that the spontaneous emission coefficient becomes a maximum at x = 0.7. Also, the light emission intensity of GaN/AlxIn1−xN QDs is shown to be greatly increased by the screening effect, irrespective of Al content in the barrier and the case with x = 0.8 shows the largest screening potential.

The thermodynamic stability of strontium monohalides dications: A theoretical exploration of the electronic states and spectroscopic parameters of SrF2+ and SrCl2+

The diatomic dications SrF2+ and SrCl2+ were investigated for the first time at a high level of theoretical approach, SA-CASSCF/MRCI. The overall energetic profile of all Λ + S states correlating with the three lowest dissociation channels, and the associated Ω states provide reliable results to characterize the lowest-lying states as thermodynamic stable. Einstein spontaneous emission coefficients evaluated for perpendicular A(1/2)–X1(3/2) transitions, and parallel and perpendicular A(1/2)–X2 (1/2) ones, and the spectroscopic parameters are expected to guide the spectroscopist in the challenging task of probing them experimentally. Similarities and differences with the CaF2+ and CaCl2+ results are discussed.

Electromagnetically induced transparency in degenerate ladder-type system

We study the effect of the electromagnetically-induced transparency on the 3-level ladder-type atomic system, with the middle level being three-fold degenerate, and show the influence of the degeneracy on the shape of both the transparency window and dispersion curve. In the theoretical description of the model, the density matrix formalism is used, with decoherence effects described by the spontaneous emission coefficients from higher to lower energy levels. The corresponding optical Bloch equations are numerically solved in the stationary regime, and the obtained results are interpreted with the help of the theoretical dressed-state analysis. The influence of the control Rabi frequency and spontaneous emission coefficients on the occurrence and properties of the transparency window, as well as the properties of the dispersion curve are also investigated. Finally, using the dressed-state analysis, together with the approximate analytical results from the perturbation theory, we show that the system with the degenerate middle level can be treated as the system without degeneracy, with the modified decay rate from the highest to the middle energy level.

ABC-model analysis of gain-switched pulse characteristics in low-dimensional semiconductor lasers

The gain-switching dynamics of low-dimensional semiconductor lasers is simulated numerically by using a two-dimensional rate-equation model. Use is also made of the ABC model, where the carrier recombination rate is described by a function of carrier densities including Shockley – Read – Hall (SRH) recombination coefficient A, spontaneous emission coefficient B and Auger recombination coefficient C. Effects of the ABC parameters on the ultrafast gain-switched pulse characteristics with high-density pulse excitation are analysed. It is found that while the parameter A has almost no obvious effects, the parameters B and C have distinctly different effects: B influences significantly the delay time of the gain-switched pulse, while C affects mainly the pulse intensity.

Piezoelectric and spontaneous polarization effects on exciton binding energy and light emission properties of wurtzite ZnO/MgO quantum dots

Exciton binding energies and light emission characteristics for wurtzite (WZ) cubic ZnO/MgO quantum dots (QDs) are investigated by considering piezoelectric (PZ) and spontaneous (SP) polarizations. These results are compared with those for the flat-band without PZ and SP polarizations. The exciton binding energies for the case with PZ and SP polarizations appears to be smaller than those for the flat-band model. In particular, the spontaneous emission coefficients are shown to be reduced significantly by the built-in field because the existence of the built-in field results in the decrease in the overlap between the electron and hole wave functions. These results show that the consideration of PZ and SP polarizations is very important in predicting optical properties of ZnO-based QD devices.

New coordination polymers based on a V-shaped ligand and lanthanides: Structural description and symmetry-luminescence correlation using europium as a probe

We have synthesized new luminescent coordination polymers using 4,4׳-sulfonyldibenzoic acid (H2SDA) and several lanthanide ions by open crystallization in DMF. Three different 1-D structures were obtained, as determined by single-crystal X-ray diffraction: [La(η2-NO3)(μ-SDA)(DMF)3]n (1), [Sm(η2-NO3)(μ-SDA)(DMF)2·2DMF]n (3), [Ln(η2-NO3)(μ-SDA)(DMF)2·DMF]n (Ln = Eu (4), Dy (5), Ho (6), Er (7), Tm (8) and Lu (9)). A 2-D structure, [Er2(η2-SDA)3(DMF)(H2O)3·2DMF]n (10), was also obtained. The measured photophysical properties of these compounds seem to be interesting for applications (high lifetime, narrow line width and high degree of color purity). In addition, emission spectra, spontaneous emission coefficients (Arad and Anrad), and intensity parameters (Ω2 and Ω4), from spectroscopic data of Eu3+, were used to evaluate crystal stabilities. Differences in the spectra acquired before and after DMF removal clearly reflected the changes taking place in the ion environment.

Theoretical studies on ultraviolet nearly lattice-matched BAlGaN/BAlGaN quantum well structures with quaternary BAlGaN barriers

Light emission characteristics of BxAlyGa1−x−yN/BAlGaN quantum well (QW) structures with quaternary BAlGaN barrier were investigated using the multiband effective-mass theory. The internal field in the BAlGaN well of the BAlGaN/AlN QW structure is shown to be large (∼10 MV/cm) under the lattice-matched condition (%). On the other hand, the internal field is significantly reduced by using BAlGaN barrier and the peak intensity of the spontaneous emission coefficient of the lattice-matched BAlGaN/BAlGaN QW structure is comparable to that of the conventional BAlGaN/AlN QW structure. We observe that the light intensity of the lattice-matched BAlGaN/BAlGaN QW structure is comparable to that of the conventional BAlGaN/AlN QW structure. Also, we observe that the nearly lattice-matched BAlGaN/BAlGaN QW structure with small strain (0.5%) has about 3 times larger peak intensity than the conventional QW AlGaN/AlN structure. Hence, BAlGaN/BAlGaN QW system could be used as a UV light source with a higher light emission and a higher crystal quality, compared to conventional AlGaN/AlN QW structures with larger strain (1.78%).

Chemical Partition of the Radiative Decay Rate of Luminescence of Europium Complexes

The spontaneous emission coefficient, Arad, a global molecular property, is one of the most important quantities related to the luminescence of complexes of lanthanide ions. In this work, by suitable algebraic transformations of the matrices involved, we introduce a partition that allows us to compute, for the first time, the individual effects of each ligand on Arad, a property of the molecule as a whole. Such a chemical partition thus opens possibilities for the comprehension of the role of each of the ligands and their interactions on the luminescence of europium coordination compounds. As an example, we applied the chemical partition to the case of repeating non-ionic ligand ternary complexes of europium(III) with DBM, TTA, and BTFA, showing that it allowed us to correctly order, in an a priori manner, the non-obvious pair combinations of non-ionic ligands that led to mixed-ligand compounds with larger values of Arad.

AsCl radical: The low-lying electronic states and the (1)3Π → X3Σ− electronic transition

Accurate potential energy curves, dissociation energies, and molecular constants for several low-lying singlet and triplet electronic states of AsCl were investigated using the CASSCF/MRCI methodology, including the spin–orbit splitting with the aug-cc-pV5Z-DK basis set. Our results represent an improvement over previous the theoretical descriptions for the lowest lying states, as well as characterize another higher excited state not previously investigated. Transition probabilities and radiative lifetimes for the (1)3Π→X3Σ− band system were also predicted using Einstein spontaneous emission coefficients.

Kinetics of general electromagnetic fluctuations in unmagnetized plasmas: aperiodic thermal noise

Any fully-ionized collisionless plasma with finite random particle velocities contains electric and magnetic field fluctuations which are of three different types: weakly damped, weakly propagating or aperiodic. The kinetics of these fluctuations in general unmagnetized plasmas is governed by the competition of spontaneous emission, absorption and stimulated emission processes. The generalized Kirchhoff laws for both collective and non-collective fluctuations are derived, which in stationary plasmas provide the equilibrium energy densities of electromagnetic fluctuations by the ratio of the respective spontaneous emission and true absorption coefficients. The equilibrium energy densities of aperiodic transverse collective electric and magnetic fluctuations in an isotropic thermal electron–proton plasma of density ne is calculated as and , where g and βe denote the plasma parameter and the thermal electron velocity in units of the speed of light. For densities and temperatures of the reionized early intergalactic medium ∣δB∣ = 6 · 10−18 G and ∣δE∣ = 2 · 10−16 G result.

Thermal fluctuation levels of magnetic and electric fields in unmagnetized plasma: The rigorous relativistic kinetic theory

Any fully ionized collisionless plasma with finite random particle velocities contains electric and magnetic field fluctuations. The fluctuations can be of three different types: weakly damped, weakly propagating, or aperiodic. The kinetics of these fluctuations in general unmagnetized plasmas, governed by the competition of spontaneous emission, absorption, and stimulated emission processes, is investigated, extending the well-known results for weakly damped fluctuations. The generalized Kirchhoff radiation law for both collective and noncollective fluctuations is derived, which in stationary plasmas provides the equilibrium energy densities of electromagnetic fluctuations by the ratio of the respective spontaneous emission coefficient and the true absorption coefficient. As an illustrative example, the equilibrium energy densities of aperiodic transverse collective electric and magnetic fluctuations in an isotropic thermal electron-proton plasmas of density ne are calculated as |δB|=(δB)2=2.8(nemec2)1/2g1/2βe7/4 and |δE|=(δE)2=3.2(nemec2)1/2g1/3βe2, where g and βe denote the plasma parameter and the thermal electron velocity in units of the speed of light, respectively. For densities and temperatures of the reionized early intergalactic medium, |δB|=6·10−18G and |δE|=2·10−16G result.

Novel Luminescent Eu3+-Indandionate Complexes Containing Heterobiaryl Ligands

Novel Ln3+-indandionate complexes of formulas [Ln(aind)3L(H2O)] and [Ln(bind)3L]∙H2O (L: 1,10-phenanthroline (phen) or 4,7-dimethyl-1,10-phenanthroline (dmphen), Ln3+: Eu3+ or Gd3+, aind: 2-acetyl-1,3-indandionate and bind: 2-benzoyl-1,3-indandionate) were synthesized and characterized by elemental analysis, infrared spectroscopy, and thermogravimetric analyses. The characterization data are consistent with the presence of a water lattice molecule in the [Ln(bind)3L]∙H2O compounds. However, the data also suggest that the water acts as a coordinated molecule in the [Ln(aind)3L(H2O)] ones. Theoretical geometries of the Eu3+-complexes have been optimized via the SPARKLE/AM1 Model for lanthanide complexes that are consistent with their luminescence experimental data. The photoluminescence properties of the Eu3+-compounds have been discussed in terms of experimental intensity parameters (Ω2 and Ω4), radiative (Arad), and non-radiative (Anrad) spontaneous emission coefficients. The higher values of emission quantum efficiency (η) of the [Eu(bind)3L]∙H2O compounds reflect the absence of luminescence-quenching water molecule in their first coordination spheres.

Optical Emission Characteristics of Pseudopolarization-Matched Green AlInGaN/InGaN Quantum Well Structures

Optical properties of pseudopolarization-matched green AlInGaN/InGaN quantum-well structures with a quaternary AlInGaN well layer were investigated by using non-Markovian gain model with many-body effects. We found that the emission peak can be enhanced by using quaternary AlInGaN well and is sensitive to the In composition in the InGaN barrier. The spontaneous emission coefficient shows a maximum at In composition of 0.22 in the barrier and gradually decreases with increasing In composition. The spontaneous emission coefficient of the AlInGaN/InGaN system with reduced internal field is shown to be increased by 70% compared to that of the conventional InGaN/GaN system. Beff of the AlInGaN/InGaN QW structure is much larger than that of the InGaN/GaN QW structure in the investigated range of the current density.

Hybrid InGaN/CdZnO quantum well structures for optoelectronic applications in the short wavelength spectral region

AbstractSpontaneous emission characteristics of hybrid InxGa1 − xN/Cd0.05Zn0.95O quantum well (QW) structures were theoretically investigated by using multi‐band effective mass theory. The transition wavelength of the InGaN/CdZnO QW structure is shown to be changed from 415 to 580 nm when the In content x is varied from 0.1 to 0.3. The conventional InGaN/GaN QW structure shows that its peak intensity linearly decreases with increasing peak wavelength. On the other hand, the InGaN/CdZnO QW structure shows that the spontaneous emission coefficient reaches a maximum at around the peak wavelength of 0.484 µm, which corresponds to x = 0.2. This can be explained by the fact that, in a range of the short peak wavelengths, the InGaN/CdZnO QW structure has a very shallow potential well. In a range of the longer peak wavelengths above 0.47 µm, the InGaN/CdZnO QW structure is expected to have a larger spontaneous emission peak than the InGaN/GaN QW structure. This can be explained by the fact that the former has a reduced internal field compared to the latter.