Optical Transition Probabilities Research Articles

Influence of Mixing Valence Band States to the Conduction Band States on Two-Quantum Linear-Circular Dicroism in Semiconductors

A quantitative theory of two-photon linear-circular dichroism caused between the subbands of light and heavy holes of the valence band and conduction band is constructed, which takes into account the admixture of valence band states to the conduction band states and the temperature dependence of the band gap (Eg(T)) in semiconductors of tetrahedral symmetry in the multiband Kane model. It is shown that the type of oscillatory angular dependence or the amplitude values of the probabilities of two-photon optical transitions depend on the state of light polarization. This is due to the fact that, under the influence of linearly polarized light, alignment along the pulse occurs, and under the action of circularly polarized light, the moments of current carriers are oriented. It has been determined that the probability of two-photon optical transitions from the heavy hole subband to the conduction band of semiconductors at a fixed temperature increases with increasing frequency, passes through a maximum, and sharply decreases regardless of the degree of polarization of light, as well as the band gap.

Photoluminescence emission enhancement in the LiSrVO4:Eu3+ vanadate phosphor by partial substitution of M+ ions (M+=Li+/Na+/K+); optical thermometry; and optical transition probabilities using Judd-Ofelt analysis

In solid state lighting (SSL), pcWLEDs gain more attention for various illumination applications. The Eu3+ activated LiSrVO4:xEu3+ (0–15 mol% in steps of 3) phosphors are prepared by the conventional solid state method and their phase formation is confirmed by PXRD. It suggest that the samples are in a monoclinic structure with P2/m space group. SEM results confirmed that the size of the prepared phosphor is in a micrometer range with an irregular spherical shape. The optical diffuse reflectance spectrum (DRS) consisted broad band absorption in the ultraviolet (UV) region (270–350 nm) and also, they are found to absorb strongly the NUV light (396 nm) and the blue light (466 nm). They exhibit the strongest emission at 617 nm for the samples under 326 nm excitation. The PL intensity of the phosphors are improved by co-doping. The optical transition probabilities of the LiSrVO4:9 mol% Eu3+ phosphor are also analyzed using the Judd-Ofelt theory. The optimized phosphor showed a good thermal stability and the lifetime values are in the millisecond range. The absolute and the relative sensitivities are obtained from the temperature dependent lifetime measurements. The LiSrVO4:9 mol%Eu3+ phosphor yielded CIE coordinates (x, y) of (0.5987, 0.4005), a low CCT of 1468K, and a color purity of 96.4 %. These results indicate the potential application of the LiSrVO4 based phosphors in WLEDs.

Density of electronic states in silicon nanocrystals embedded in a SiO2 matrix and passivated by hydrogen

Subject of study. This study is devoted to the optical transitions and density of electron and hole states in silicon nanocrystals embedded in a SiO2 dielectric matrix and silicon nanocrystals passivated by hydrogen. Aim of study. The aim is to calculate the probability of optical transitions, density of electron and hole states, and absorption cross-section in silicon nanocrystals surrounded by different environments. Another goal is to adapt the tight-binding method for correct passivation of dangling bonds of silicon. Method. The calculations are performed using the variant of the tight-binding method that accounts for a large number of orbitals: s, p, d, and s∗. Main results. The local density of states of electrons and holes, probabilities of optical transitions, and absorption cross-sections of silicon nanocrystals passivated by hydrogen and nanocrystals embedded in a SiO2 matrix were calculated. It is shown that the electron and hole states in hydrogen-passivated silicon nanocrystals are localized within the crystal, and optical transitions occur at wavelengths in the range of 440–620 nm. The presence of the SiO2 matrix surrounding the nanocrystal increases the probability of optical transitions and leads to the appearance of the local density of states outside the nanocrystal, with radiative emission in the wavelength range of 410–620 nm. Practical significance. The results highlight the feasibility of utilizing silicon nanocrystals in photonics and photovoltaics. They are expected to contribute to the development of technology for creating silicon nanocrystals with specific optical properties.

Solid-state quantum nodes based on color centers and rare-earth ions coupled with fiber Fabry–Pérot microcavities

High-performance optical quantum memories serving as quantum nodes are crucial for the distribution of remote entanglement and the construction of large-scale quantum networks. Notably, quantum systems based on single emitters can achieve deterministic spin-photon entanglement, greatly simplifying the difficulty of constructing quantum network nodes. Among them, optically interfaced spins embedded in solid-state systems, as atomic-like emitters, are important candidate systems for implementing long-lived quantum memory due to their stable physical properties and robustness to decoherence in scalable and compact hardware. To enhance the light-matter-interaction strength, optical microcavities can be exploited as an important tool to generate high-quality spin-photon entanglement for scalable quantum networks. They can enhance the photon collection probability and photon generation rate of specific optical transitions and improve the coherence and spectral purity of emitted photons. For solid-state systems, open Fabry-Pérot cavities can couple single emitters that are not in proximity to the surface, avoiding significant spectral diffusion induced by the interfaces while maintaining the wide tunability, whichenables addressing of multiple single emitters in the frequency and spatial domain within a single device. This review describes the characteristics of single emitters as quantum memories with a comparison to atomic ensembles, the cavity-enhancement effect for single emitters and the advantages of different cavities, especially fiber Fabry-Pérot microcavities. Finally, recent experimental progress on solid-state single emitters coupled with fiber Fabry-Pérot microcavities is reviewed, with a focus on color centers in diamond and silicon carbide, as well as rare-earth dopants.

Effect of co-doping alkali metal ions Li+/Na+/K+ on the photoluminescence enhancement properties of the near white light emitting LiSrVO4:Dy3+ phosphor along with the optical transition probabilities by Judd-Ofelt analysis for WLEDs application

Effect of co-doping alkali metal ions Li+/Na+/K+ on the photoluminescence enhancement properties of the near white light emitting LiSrVO4:Dy3+ phosphor along with the optical transition probabilities by Judd-Ofelt analysis for WLEDs application

Spectral Broadening of a Single Er3+ Ion in a Si Nanotransistor

Single rare-earth ions in solids show great potential for quantum applications, including single photon emission, quantum computing, and high-precision sensing. However, homogeneous linewidths observed for single rare-earth ions are orders of magnitude larger than the sub-kilohertz linewidths observed for ensembles in bulk crystals. The spectral broadening creates a significant challenge for achieving entanglement generation and qubit operation with single rare-earth ions, so it is critical to investigate the broadening mechanisms. We report a spectral broadening study on a single Er$^{3+}$ ion in a Si nano-transistor. The Er-induced photoionisation rate is found to be an appropriate quantity to represent the optical transition probability for spectroscopic studies, and the single ion spectra display a Lorentzian lineshape at all optical powers in use. Spectral broadening is observed at relatively high optical powers and is caused by spectral diffusion on a fast time scale.

Photochemical anisotropy and direction-dependent optical absorption in semiconductors.

Photochemical reactions on semiconductors are anisotropic, since they occur with different rates on surfaces of different orientations. Understanding the origin of this anisotropy is crucial to engineering more efficient photocatalysts. In this work, we use hybrid density functional theory to identify the surfaces associated with the largest number of photo-generated carriers in different semiconductors. For each material, we create a spherical heat map of the probability of optical transitions at different wave vectors. These maps allow us to identify the directions associated with the majority of the photo-generated carriers and can, thus, be used to make predictions about the most reactive surfaces for photochemical applications. The results indicate that it is generally possible to correlate the heat maps with the anisotropy of the bands observed in conventional band structure plots, as previously suggested. However, we also demonstrate that conventional band structure plots do not always provide all the information and that taking into account the contribution of all possible transitions weighted by their transition dipole moments is crucial to obtain a complete picture.

Engineering of the Photon Local Density of States: Strong Inhibition of Spontaneous Emission near the Resonant and High-Refractive Index Dielectric Nano-objects.

Metallic or dielectric nano-objects change the photon local density of states of closely placed emitters, particularly when plasmon or Mie resonances are present. Depending on the shape and material of these nano-objects, they may induce either a decrease or an increase in decay rates of the excited states of the emitter. In this work, we consider the reduction of the probability of optical transitions in emitters near high-refractive index dielectric (silicon and zinc selenide) nanoparticles. We tune the spectral positions of magnetic and electric modes of nanocylinders to obtain the largest overlap of the valleys in the total decay rate spectra for differently oriented dipoles and, in this way, find the highest inhibition of about 80% for randomly oriented emitters. The spectral positions of these valleys are easy to control since the wavelengths of the modes depend on the height and diameter of nanocylinders. The inhibition value is robust to the distance between the emitter and the nanoparticle in the range of nearly 50 nm, which is crucially important for the applications, such as selective optical transition engineering and photovoltaics.

Ferroelectric Properties and Spectroscopic Characterization of Pb(Mg1/3Nb2/3)O3-32PbTiO3:Er3+/Sc3+ Crystal

An Er3+/Sc3+ co-doped 0.68Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 ferroelectric single crystal was grown by high-temperature flux method. The remnant polarization Pr is 27.97 µC/cm2 and the coercive field Ec is 8.26 kV/cm for [100] oriented crystal. Green (524 and 551 nm) and red (654 nm) emission bands are generated at the 980 nm excitation, which corresponds to the 2H11/2→ 4I15/2, 4S3/2→ 4I15/2 and 4F9/2→ 4I15/2 transitions of Er3+, respectively. Judd–Ofelt theory has been applied to predict the spectroscopic characteristics of the as-grown crystals. The obtained J–O intensity parameters Ωt (t = 2, 4 and 6) are Ω2 = 0.76 × 10−20 cm2, Ω4 = 1.0 × 10−20 cm2, Ω6 = 0.55 × 10−20 cm2. Spectroscopic characteristics, including optical transition probabilities, branching ratio, and radiative lifetime of Er3+ in the crystal, are determined. The calculated radiative lifetimes of 4I13/2 and 4I11/2 energy levels are 2.82 ms and 2.61 ms, respectively. These investigations provide possibilities for the crystal Pb(Mg1/3Nb2/3)O3-0.32PbTiO3:Er3+/Sc3+ to be a new type of multifunctional crystal integrating electricity-luminescence.

Structure, and opto-dielectric investigations of Cu2+ -doped calcium bismuth silicate glass ceramics

CuO inclusive silicate glasses are well known for various semiconductor applications. However, there is a lot of demand and necessity of high efficient opto-dielectric materials. In view of this, the glasses of chemical composition (30 – x) CaO + (10) Bi2O3 + (60) SiO2 + (x) CuO have been synthesized and studied for their structural, optical and dielectric characterization techniques. Glassy behaviour of CuO undoped glass and ceramic behaviour of all other CuO doped glasses conformed by structural characterization. The elastic modulus and micro hardness of glass and glass ceramics reveal their inter connected covalent structure. Trap depth parameters (Tm, Eτ, Eδ, Eω & μs) have been determined and analysed under irradiation, and found that 0.3 mol% CuO -doped glass ceramic under 30 kGy of irradiation dose exhibiting better TL output. Dielectric relaxation studies of the glass ceramics suggested that mixed conduction of both ionic and electronic. Observed dielectric results; dielectric constant (εr), dielectric loss (tanφ), temperature region of relaxation (ΔT), low activation energie's for conduction (Ea) and AC Conductivity (σac) suggesting that the glass ceramics are dielectric. Optical band gap (Eo), transition probability (At) and emission cross section (σ) corresponding to the emissive transition 3D1 → 1S0 assessed by optical techniques. All the results suggests that 0.3 mol% CuO -doped glass ceramic is a useful opto-dielectric resource.

Resonant Photoluminescence of a Two-Dimensional Electron System upon the Formation of a Bulk 1/3 State of the Fractional Hall Effect

Resonant and nonresonant photoluminescence spectra of a two-dimensional electron system have been studied under the conditions of the formation of the 1/3 fractional quantum Hall effect state. It has been shown that resonant photoluminescence, in contrast to nonresonant photoluminescence, is a universal marker of the formation of the 1/3 state in the bulk of the two-dimensional system. It has been found that the probabilities of optical transitions from the zeroth Landau level of electrons in the 1/3 state vary so strongly that these variations cannot be explained within the existence theoretical concepts.

Predicting Inorganic Photovoltaic Materials with Efficiencies >26% via Structure-Relevant Machine Learning and Density Functional Calculations

Summary Discovering new inorganic photovoltaic materials becomes an efficient way for developing a new generation of solar cells with high efficiency and environmental stability. Using machine learning (ML) and density functional theory calculations, we report four promising inorganic photovoltaic materials—Ba4Te12Ge4, Ba8P8Ge4, Sr8P8Sn4, and Y4Te4Se2—demonstrating notable theoretical photovoltaic performance for use in solar cells. The symmetry-allowed optical transition probability, the large amount of density of states near the conduction band minimum (CBM) and the valence band maximum (VBM), and the strong p-p transition across the band edge contribute to the large optical absorption coefficient, leading to the outstanding theoretical power conversion efficiency (PCE). The separation of the VBM and CBM wave function distributions contribute to the fast separation of the photogenerated electrons and holes and the enhanced carrier lifetimes. Our ML model is an efficient method for fast and atomic-level accuracy prediction of photovoltaic materials with different crystal structures.

Analysis of the hyperfine structure of the Cs2[formula omitted] state

We report on theoretical calculations and analyses of the hyperfine structures in the spectra of the Cs233Σg+ state observed by Li et al by infrared-infrared (IR-IR) double resonance spectroscopy in 2008. For this purpose, we consider the excitation–de-excitation schemes in their entirety, taking into account the mixed character of the intermediate levels of the A1Σu+∼b3ΠΩu system, which generally contains contributions from all Ω=0,1,2 basis states. We also avoid an approximation for the strongest features in the spectra (the major component), in which the probabilities of optical dipole transitions are computed from 0-th order state vectors alone. We compute the contributions from all components of the mixed states. The fundamental theory and algorithms are described, the parameters of the chosen model are fitted and reported, and the results of the simulation are presented.

Nonparabolicity of size-quantized subbands of bilayer semiconductor quantum wells with heterojunction.

This paper presents a theory of size quantization and intersubband optical transitions in bilayer semiconductor quantum wells with asymmetric profile. We show that, in contrast to single-layer quantum wells, the size-quantized subbands of bilayer quantum wells are nonparabolic and characterized by effective masses that depend on the electron wave number and the subband number. It is found that the effective masses are related to the localization of the electron wave function in the layers of the quantum well and can be controlled by varying the chemical composition or geometric parameters of the structure. We also derive an analytical expression for the probability of optical transitions between the subbands of the bilayer quantum well. Our results are useful for the development of laser systems and photodetectors based on colloidal nanoplates and epitaxial layers of semiconductor materials with heterojunctions.

Density Functional Theory Study of ZnIn2S4 and CdIn2S4 Polymorphs Using Full‐Potential Linearized Augmented Plane Wave Method and Modified Becke–Johnson Potential

ZnIn2S4 and CdIn2S4 are ternary sulfide semiconductors with attracting photoelectric and catalytic properties, which are closely related with their band structure. The full‐potential linearized augmented plane wave (FP‐LAPW) method is used to calculate the band structures of cubic and hexagonal polymorphs of ZnIn2S4 and CdIn2S4. Among the four systems studied, the hexagonal CdIn2S4 structure with a space group P63mc (No. 186) is newly predicted, and the phonon calculation shows that its structure is dynamically stable. Owing to the well‐known bandgap underestimation problem of local density approximation (LDA) and generalized gradient approximation (GGA), the effects of Hubbard model and modified Becke–Johnson (mBJ) potential to band structure are investigated. The calculated outcomes of cubic ZnIn2S4 and cubic CdIn2S4 with mBJ‐GGA + U are in good agreement with the experimental data. For hexagonal ZnIn2S4, it is shown that electronic states in high valence bands and low conduction bands have different components. The origin of discrepancy between the theoretical bandgap of hexagonal ZnIn2S4 and experimental value obtained from optical absorption measurement is discussed based on the spatial separation of electron and hole states and optical transition probability.

Correlation with one- and two-photon absorptions in Bi2O3 containing B2O3 and SiO2 glasses with zero photoelastic constant

One- and two-photon absorption coefficients in Bi2O3–B2O3 and Bi2O3–SiO2 glasses, which are characterized with zero photoelasticity and visible transparency, are studied. The two systems show a similar compositional dependence in photoelastic constant (PEC), which can be accounted for by electronic structure of Bi3+. The one-photon absorption coefficients in borate and silicate glasses depend on the existence of charge transfer phenomena, while the two-photon absorption coefficients obtained by Z-scan measurement is independent of the one-photon absorption. The interpretation by optical transition probabilities can be extended to elucidate the optical nonlinearity in ns2-type cation containing oxide glasses with zero PEC.

Anisotropic Nonlinear Optical Properties of a SnSe Flake and a Novel Perspective for the Application of All‐Optical Switching

AbstractThe deceptively simple tin selenide (SnSe) film has emerged as an appealing 2D material with a narrow bandgap, high charge carrier mobility, and significant thermoelectric figure of merit. In particular, compared with most commonly investigated 2D materials, SnSe with a puckered honeycomb structure possesses a lower lattice symmetry, resulting in prominent in‐plane anisotropy. Herein, with polarization‐dependent Raman spectroscopy and polarization‐dependent nonlinear absorption measurements, pronounced polarization‐dependent nonlinear optical properties of a SnSe flake are demonstrated originating from the anisotropic optical transition probability of SnSe, which is confirmed by ultrafast polarization‐dependent pump–probe experiments. Furthermore, a novel SnSe‐based all‐optical switch is proposed and experimentally explored. Specifically, due to the polarization‐dependent nonlinear optical response of SnSe, this all‐optical switch can access the “ON” and “OFF” modes of continuous‐wave signal light (633 nm, 13 µW) by altering the polarization of the switching light (800 nm, 65 fs, 1 kHz, 34 GW cm−2), rather than modifying its intensity, achieving an unexpectedly high ON/OFF ratio (the difference of the normalized transmittance of signal light between “ON” and “OFF” modes) of 44%. This work opens up real perspectives for versatile optoelectronic devices based on SnSe materials.

Peculiarities of the energy spectrum of InSb/InAs/InGaAs/InAlAs/GaAs nanoheterostructures revealed by room temperature photomodulation FTIR spectroscopy

Fourier-transform infrared photoreflectance was used to optimize design and growth temperature of complex III–V nanoheterostructures proposed for efficient mid-IR emitters. They comprised an InAs/InGaAs quantum well (QW) with InSb sub-monolayer insertions and were grown by molecular beam epitaxy on GaAs substrates via a convex-graded InAlAs metamorphic buffer layer. The room temperature photoreflectance spectra supported by the full 8 × 8 Kane model calculations showed that the triple InSb insertions enhance the probability of the main optical transitions in the QW, while lowering the growth temperature results in a red shift of the transitions and further increase in their probability.

Interband transitions in narrow-gap carbon nanotubes and graphene nanoribbons

We use the robust nearest-neighbor tight-binding approximation to study the same footing interband dipole transitions in narrow-bandgap carbon nanotubes (CNTs) and graphene nanoribbons (GNRs). It is demonstrated that curvature effects in metallic single-walled CNTs and edge effects in gapless GNRs not only open up bandgaps, which typically correspond to THz frequencies, but also result in a giant enhancement of the probability of optical transitions across these gaps. Moreover, the matrix element of the velocity operator for these transitions has a universal value (equal to the Fermi velocity in graphene) when the photon energy coincides with the bandgap energy. Upon increasing the excitation energy, the transition matrix element first rapidly decreases (for photon energies remaining in the THz range but exceeding two bandgap energies, it is reduced by three orders of magnitude), and thereafter it starts to increase proportionally to the photon frequency. A similar effect occurs in an armchair CNT with a bandgap opened and controlled by a magnetic field applied along the nanotube axis. There is a direct correspondence between armchair GNRs and single-walled zigzag CNTs. The described sharp photon-energy dependence of the transition matrix element, together with the van Hove singularity at the bandgap edge of the considered quasi-one-dimensional systems, makes them promising candidates for active elements of coherent THz radiation emitters. The effect of Pauli blocking of low-energy interband transitions caused by residual doping can be suppressed by creating a population inversion using high-frequency (optical) excitation.

Optical transition probabilities of white light emitting Sr2SiO4:Dy3+ nanophosphors for lighting applications using Judd−Ofelt analysis

Dysprosium doped strontium silicate (Sr2-xSiO4:xDy3+, x = 0–7 mol%) are prepared by solution combustion synthesis and their luminescent behaviour is investigated. X-ray diffraction (XRD) reveals the structure to be orthorhombic in nature and different structural parameters are calculated. The photoluminescence excitation and emission spectra are thoroughly discussed. The emission spectra excited at 350 nm showed the characteristic blue and yellow emission, the admixture of which gives probable white emission. Further, the absorption spectrum is used to systematically study the spectral intensities of Sr2-xSiO4:xDy3+ (x = 0.008) nanophosphors using Judd-Oflet (JO) theory. The JO parameters thus obtained followed the trend Ω2>Ω6>Ω4 that revealed the field surrounding the ions lack inversion symmetry and is also confirmed by asymmetric ratios. JO parameters are also used to study different radiative properties. The magnitude of the calculated peak emission cross section for the transition 4F9/2 → 6H13/2 is 1.02 × 10−20 cm2, a value suitable for laser applications. An energy transfer quenching mechanism indicates that the mode of non-radiative transition is dominated by dipole-dipole interactions. Color coordinates and color correlated temperature with respect to different Dy3+ concentrations are studied in detail.