Spin-orbit Splitting Energy Research Articles

Tunable charge transport properties in non-stoichiometric SrIrO3 thin films

Delving into the intricate interplay between spin-orbit coupling and Coulomb correlations in strongly correlated oxides, particularly perovskite compounds, has unveiled a rich landscape of exotic phenomena ranging from unconventional superconductivity to the emergence of topological phases. In this study, we have employed pulsed laser deposition technique to grow SrIrO3 (SIO) thin films on SrTiO3 substrates, systematically varying the oxygen content during the post-deposition annealing. X-ray photoelectron spectroscopy (XPS) provided insights into the stoichiometry and spin-orbit splitting energy of Iridium within the SIO film, while high-resolution x-ray studies meticulously examined the structural integrity of the thin films. Remarkably, our findings indicate a decrease in the metallicity of SIO thin films with reduced annealing O2 partial pressure. Furthermore, we carried out magneto-transport studies on the SIO thin films, the results revealed intriguing insights into spin transport as a function of oxygen content. The tunability of the electronic band structure of SIO films with varying oxygen vacancy is correlated with the density functional theory calculations. Our findings elucidate the intricate mechanisms dictating spin transport properties in SIO thin films, offering invaluable guidance for the design and optimization of spintronic devices based on complex oxide materials. Notably, the ability to tune bandwidth by varying post-annealing oxygen partial pressure in iridate-based spintronic materials holds significant promise for advancing technological applications in the spintronics domain.

Luminescence and Covalency in Ytterbium-Doped CrX3 (X = Cl, Br, I) van der Waals Compounds.

The layered 2D van der Waals ferromagnets CrX3 (X = Cl, Br, I) show broad d-d photoluminescence (PL). Here we report preparation, structural characterization, and spectroscopic studies of all three CrX3 compounds doped with the optical impurity, Yb3+. EXAFS measurements show very similar Cr K-edge and Yb L-edge data for each doped compound, and good fits of the latter are obtained for structures having Yb3+ occupying substitutional octahedral sites. Yb-X bond lengths are systematically ∼0.25 Å larger than their Cr-X counterparts. 4 K PL measurements show efficient sensitization of Yb3+ luminescence upon photoexcitation into lattice absorption bands [Cr3+ d-d and ligand-to-metal charge-transfer (LMCT)] for all three compounds, converting their nondescript broadband d-d PL into sharp f-f emission. The PL of CrCl3:Yb3+ and CrBr3:Yb3+ occurs at energies typical for [YbX6]3- with these halides, with PL decay times of 0.5-1.0 ms at 4 K, but CrI3:Yb3+ displays anomalously low-energy Yb3+ emission and an unusually short PL decay time of only 8 μs at 4 K. Data analysis and angular overlap model (AOM) calculations show that Yb3+ in CrI3:Yb3+ has a lower spin-orbit splitting energy than reported for any other Yb3+ in any other compound. We attribute these observations to exceptionally high covalency of the Yb3+ f orbitals in CrI3:Yb3+ stemming primarily from the shallow valence-shell ionization potentials of the iodide anions.

Structural, vibrational and electronic properties of Nb substituted orthovanadates LaV1−xNbxO4

We investigate the structural, vibrational, morphological, and electronic properties of Nb substituted orthovanadate LaV1−xNbxO4 samples prepared by the solid-state reaction method. The x-ray diffraction (XRD) analysis reveals the presence of three crystal structures [monoclinic monazite (m − m) type for the x = 0, two-phase equilibrium of monoclinic monazite (m − m) and tetragonal scheelite (t − s) type for the 0.2 ≤ x ≤ 0.8, and monoclinic fergusonite (m − f) type for the x = 1 samples] with an increase in Nb5+ concentration. The Raman spectroscopy and x-ray photoelectron spectroscopy (XPS) were employed to study the vibrational and electronic properties of all the samples, respectively. In order to choose an excitation wavelength that does not cause undesirable fluorescence and has observable intensities of all the vibrational modes, the Raman spectra are collected using 532 nm, 633 nm, and 785 nm laser lines. With increasing the Nb5+ concentration, new Raman modes associated with Nb-bonds are clearly visible and the intensity of V-bonds assigned modes is decreasing. The XPS analysis shows the unchanged 3+ oxidation state of La ion where the intensity of the V 2p core-level decreases while the Nb 3d core-level increases with x. The equal spin-orbit energy splitting of the states is confirmed by the average energy difference (across La core-level spectra for all the samples) for state I as well as bonding and anti-bonding of state II. Interesting, the relative intensity of La 3d state I and state II show systematic change with Nb doping altering the metal ligand overlap. We discuss and provide insight into the evolution of the structural, morphological, and chemical features with Nb substitution in LaV1−xNbxO4 samples.

Effect of annealing temperature on supercapacitive performance of SILAR-grown Mn3O4 nanoflakes

The effect of annealing temperature on Mn3O4 thin films for their electrochemical energy-storing performance was studied. The Mn3O4 thin films were synthesized by the successive ionic layer absorption and reaction (SILAR) method. The annealing temperature was varied from 50 to 350 °C and their subsequent impact on structural, morphological, and electrochemical properties were analyzed. X-ray diffraction studies confirmed that the Mn3O4 thin films had a tetragonal hausmannite structure, which was further confirmed by X-ray photoelectron spectroscopy, wherein a spin-orbit splitting energy of 11.69 eV was observed in the Mn 2p3/2 and Mn 2p1/2 doublet states. The effect of annealing on morphological modifications was investigated using SEM analysis. The as-deposited amorphous Mn3O4 thin films having granular nanoclusters were further modified into nanoflakes by increasing the annealing temperature. Charge storage kinetics were studied using cyclic voltammetry and electrochemical impedance spectroscopy. The Mn3O4 thin films annealed at 250 °C have the highest specific capacitance of 87.84 mF/cm2 at 2.5 mA/cm2 with 97.62 % of coulombic efficiency. Moreover, the electrochemical stability of 82 % after 2000 CV cycles confirmed the potential candidature for the design and development of potential energy-storing Mn3O4 electrodes for future wearable and electronic device applications.

Structural morphological and band gap studies of Al doping in BaSnO3

In this work the role of Al as dopant in BaSnO3 is explored through structural, morphological, compositional and optical studies. The Perovskite structured pure BaSnO3 (BSO) and Al doped BSO 3D nano particles were synthesised through coprecipitation method at pH-13 using BaCO3, SnCl4 and Al2O3 as precursors. Al doped BSO was prepared by mixing BSO (taken from oven before calcinations) with Al2O3 through mortar pestle for one hour and then calcined it at 1100℃ and name it as Al doped BSO. The structural, morphological, compositional and optical studies were carried out through XRD, FESEM, XPS and Uv–Vis spectroscopy respectively. The pure and doped BSO XRD studies reveal that Al doped BSO is a multiphase material with SnO2 as a dominant phase while in pure BSO SnO2 phase was present as impurity phase. The XRD results are in correlation with the XPS results. Through XPS it is observed that Al is active dopant which suppresses the Ba incorporation in BSO and hence results in suppressed BSO phase in Al doped BSO. XPS confirms the Al doping and the spin orbit splitting energy at 8.5 eV of Sn signifies the Sn4+ incorporation, Ba as Ba2+, O as O2– and Al as Al3+. Also, there is noticeable shift of O1s XPS peak towards lower B.E in Al doped sample which is indicative of dopants presence. FESEM studies shows that agglomerated nanoparticles were formed in pure BSO and Al doped samples it seems that Al doping further enhances the agglomeration and increases the average particle size from 300 nm to 600 nm. Uv–Vis studies shows that multiphase Al doped BSO is indirect band gap material for 2.4 eV and direct band gap at 3.3 eV while pure BSO has 2.6 eV as indirect and 2.9 as direct bandgap. Optical studies lead to the conclusion that with Al doped BSO is more transparent in the visible region than pure BSO whereas in pure BSO direct transitions are happening at 427 nm.

Gain and Excess Noise in HgCdTe e-Avalanche Photodiodes at Various Temperatures and Wavelengths

Avalanche photodiodes (APDs) can amplify the weak optical signal as well as enable higher receiver sensitivity due to the internal avalanche gain, but the impact ionization process can also introduce the “excess noise”, which limits the practically achievable signal-to-noise ratio (or sensitivity) and gain-bandwidth product. Hg <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text{1} -\textit{x}}$</tex-math> </inline-formula> Cd <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\textit{x}}$</tex-math> </inline-formula> Te electron-initialed APDs (e-APD) have been demonstrated to exhibit high performance in terms of gain and excess noise at 77 K. Here, we discuss the gain and excess noise properties of multiple Hg <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text{1}-\textit{x}}$</tex-math> </inline-formula> Cd <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\textit{x}}$</tex-math> </inline-formula> Te e-APDs with different Cd compositions targeting at short-wavelength infrared (SWIR), mid-wavelength infrared (MWIR), and long-wavelength infrared (LWIR) band operating at various temperatures. It demonstrates that the gain of APDs increases as the temperature decreases and the cutoff wavelength of the devices increases, which is related to the decrease of electron effective mass, optical photon scattering rate, and bandgap of the materials. In addition, the low excess noise of less than 1.6 at high gains is also achieved for the devices over a wide range of temperatures. The large spin-orbit splitting energy ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta $</tex-math> </inline-formula> so) in comparison to bandgap energy is considered to be responsible for the observed pure electron avalanche and exceptionally low excess noise. This work may provide insight into the low-noise HgCdTe APDs and is beneficial for the future applications of high-temperature operating and high-performance optical receivers.

A comparative analysis of ZnCdTe and ZnCdTeO semiconductor alloys as competent materials for optoelectronic applications

In this paper, we report the comparative study of some parameters of II–VI ternary alloy ZnCdTe and II–VI–O dilute oxide ZnCdTeO. The purpose of this comparative study is to establish both the ternary and quaternary alloys as superior materials for optoelectronic and solar cell applications in which the quaternary materials show more superiority than the ternary material. In this purpose, we take the data from the experiments previously done and published in renowned journals and books. The parameters of these alloys are mainly being calculated using Vegard’s law and interpolation method of those collected data. It was certainly demonstrated that the incorporation of O atoms produces a high bandgap ([Formula: see text]) reduction in host ZnCdTe (Zn[Formula: see text]CdxTe) in comparison to the bandgap reduction in host ZnTe material with Cd incorporation. The bandgap of ZnCdTeO (Zn[Formula: see text]CdxTe[Formula: see text]Oy) was found to be reduced to 1.1357 at [Formula: see text] and the spin–orbit splitting energy ([Formula: see text]) value of ZnCdTeO was calculated to be 1.175[Formula: see text]eV for Cd concentration of 0.5[Formula: see text]mole and O concentration of 0.1[Formula: see text]mole both of which showed excellent results with the prospect of optoelectronic and solar cell applications. The constant rise in the spin–orbit curve signifies a very less internal carrier recombination which decreases the leakage current and augments the efficiency of solar cell. The lattice constants and strain calculation values give very good results and confirm the stability of the materials. Besides, the calculated band offsets values show that for ZnCdTeO, there is higher bandgap reduction than that of ZnCdTe. Moreover, ZnCdTeO covers a wide range of wavelength in the visible region starting from violet region at 393[Formula: see text]nm upto red region at 601[Formula: see text]nm. Both ZnCdTe and ZnCdTeO are found to have excellent applications in optoelectronic and solar cell devices though quaternary ZnCdTeO proves much supremacy over ternary ZnCdTe in all aspects of the properties.

Accurate Spin-Orbit Coupling by Relativistic Mixed-Reference Spin-Flip-TDDFT.

Relativistic mixed-reference spin-flip (MRSF)-TDDFT is developed considering the spin-orbit coupling (SOC) within the mean-field approximation. The resulting SOC-MRSF faithfully reproduces the experiments with very high accuracy, which is also consistent with the values by four-component (4c) relativistic CASSCF and 4c-CASPT2 in the spin-orbit-energy splitting calculations of the C, Si, and Ge atoms. Even for the fifth-row element Sn, the SOC-MRSF yielded accurate splittings (∼ 3 % error). In the SOC calculations of the molecular 4-thiothymine with a third-row element, SOC-MRSF values are in excellent agreement with those of the SO-GMC-QDPT2 level, regardless of geometries and exchange-correlation functionals. The same SOC-MRSF predicted the anticipated chance of S1 (nπ*) → T1 (ππ*) intersystem crossing, even in thymine with only second-row elements. With its accuracy and practicality, thus, SOC-MRSF is a promising electronic structure protocol in challenging situations such as nonadiabatic molecular dynamics (NAMD) incorporating both internal conversions and intersystem crossings in large systems.

Theoretical exploration of the optoelectronic properties of InAsNBi/InAs heterostructures for infrared applications: A multi-band k·p approach

We have investigated numerous electronic and optical aspects of the InAsNBi material, considering a multi-band k·p Hamiltonian. We have scrutinised electronic band dispersion, changes in spin–orbit splitting energy (so), charge carrier effective mass, band offset, and optical gain variations of InAsNBi and Quantum Well (QW) structures lattice-matched to InAs. The band gap of InAs0.9209N0.0291Bi0.05 is observed to be 131 meV under lattice-matched conditions, and the operating wavelength equivalent to this bandgap is 9.46 μm, which corresponds to the atmospheric Long Wavelength Infrared (LWIR) communication window of 8–12 μm. In order to tune the bandgap of a quantum confined heterostructure over a wide range, strain analysis plays a pivotal role. While compressive strain of 0.7% offers a band gap of 96 meV, tensile strain of 1.16% generates a band gap to 178 meV, which is almost equivalent to the room temperature bandgap of InSb. Under the influence of strain, spin-orbit splitting energy (Δso) spans the range from 0.31 eV to 0.45 eV. In addition to this, the inclusion of N and Bi into InAs reduces the effective mass of electrons to 0.01343 m0, which is ∼0.5 times of InAs. We have also computed the band structure of the InAsNBi/InAs QW heterostructure and found that under the influence of tensile strain with N = 2.5% and Bi = 1%, there is a changeover from Type-I to Type-II heterostructure. Indeed, InAsNBi can be a potential material for realizing various optoelectronic applications such as atmospheric LWIR communication, intermediate band solar cells, and night vision cameras.

Defect dipole induced improved electrocaloric effect in modified NBT-6BT lead-free ceramics

The Rietveld refinement of the polycrystalline powders of 1% Fe and Mn-doped (Na0.5Bi0.5)0.94Ba0.06Ti0.98V0.02O3 at the Ti-site confirmed a single rhombohedral (R3c) phase. The bandgap, (Eg) was affected by the anti-phase octahedral tilt angle and the spin-orbit splitting energy of Ti4+2p3/2 and Ti4+2p1/2 states. The decrease in Bi loss and increase in the binding energy of Ba due to Fe/Mn doping has been correlated to the strengthening of Bi-O and Ba-O bonds which was revealed from the XPS studies thereby further related to the average A-O bond length from structural studies. Hence, a reduction of oxygen vacancy (VO) for the doped samples has been justified. A significant improvement of the dielectric constant, relaxation time (τ0), and the decrease in conductivity due to doping was revealed from the frequency-dependent (10 Hz-1 MHz) dielectric measurement study. The conduction and relaxation process are dominated by the short-range movement of defects. The activation energy (Ea~1 eV) revealed that there is a presence of double-ionized VOs. The ECE study showed a significant enhancement of the changes in entropy, ΔS, and the adiabatic temperature difference, ΔT, due to doping, with ΔT being highest in the Fe-doped sample. Such improvement of dielectric and ECE properties was confirmed due to the reduction of the mobility of oxygen vacancy because of the formation(MnTi′′−Vo••)/(MnTi′−Vo••)• and FeTi′′−Vo••/(FeTi′−Vo••)• defect dipoles.

First principles calculation of electronic properties and effective mass of zinc-blende GaN

Based on the first principle pseudopotential plane wave method, the electronic structure of zinc-blende semiconductor GaN is calculated. Using the relativistic treatment of valence states, the spin orbit splitting energy of valence band top near the center of Brillouin region is calculated. Based on the effective mass approximation theory, the effective mass of electrons near the bottom of the conduction band and the effective mass of light and heavy holes near the Γ point along the directions of [100], [110] and [111] are calculated. These parameters are valuable and important parameters of optoelectronic materials.

Influence of the spin-orbit split-off valence band on the hole g factor in semiconductor nanocrystals

We present results of $\mathbit{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbit{p}$ calculations of the effective $g$ factor of holes confined in spherical, cube, and planar semiconductor nanocrystals (NCs). We use the six-band Luttinger model for semiconductors with the zinc-blende crystal structure and study the size dependence of the ${\mathrm{\ensuremath{\Gamma}}}_{8}$ top valence subband hole $g$ factor caused by the admixture of the spin-orbit split-off valence subband ${\mathrm{\ensuremath{\Gamma}}}_{7}$. We present semianalytical expressions for the hole $g$ factor which depends on the light- to heavy-hole effective mass ratio $\ensuremath{\beta}$ and on the ratio between spin-orbit energy splitting of valence band ${\mathrm{\ensuremath{\Delta}}}_{\text{SO}}$ and the hole quantization energy ${E}_{h}$. The admixture of ${\mathrm{\ensuremath{\Gamma}}}_{7}$ states is significant for small ${\mathrm{\ensuremath{\Delta}}}_{\text{SO}}/{E}_{h}$ and, in spherical and cube NCs, leads to a strong size dependence of the hole $g$ factor. In thin planar nanoplatelets (NPLs) with infinite or large lateral sizes, the dependence of the heavy-hole $g$ factor on NPL thickness is relatively weak. It is drastically enhanced and may become nonmonotonic in NPLs with finite in-plane sizes due to the additional hole states mixing. We discuss our results in comparison with published experimental data for CdSe- and InP-based spherical NCs and NPLs and point out the specificity of extracting hole $g$ factor from the data measured on excitons.

Structural, electronic, and transport properties of Janus GaInX 2 (X = S, Se, Te) monolayers: first-principles study

Two-dimensional Janus monolayers have outstanding electronic and transport properties due to their asymmetric atomic structures. In the present work, we systematically study the structural, electronic, and transport properties of the Janus GaInX 2 (X = S, Se, Te) monolayers by using the first-principles calculations. The stability of the investigated monolayers is confirmed via the analysis of vibrational spectrum and molecular dynamics simulations. Our calculations demonstrate that while GaInS2 and GaInSe2 monolayers are direct semiconductors, GaInTe2 monolayer exhibits the characteristics of an indirect semiconductor. The band gap of GaInX 2 decreases when the chalcogen element X varies from S to Te. Obtained results reveal that small spin–orbit splitting energy in the valence band is found around the Γ point of the Brillouin zone when the spin–orbit coupling is included. Interestingly, GaInS2 and GaInSe2 have high and directional isotropic electron mobility meanwhile the directional anisotropy of the electron mobility is found in the Janus GaInTe2 monolayer. Our findings not only present superior physical properties of GaInX 2 monolayers but also show promising potential applications of these materials in nanoelectronic devices.

Investigation of optoelectronic and thermoelectric properties of InAsBi for LWIR applications: A first principles and k dot p study

Systematic study on the incorporation effect of dilute Bismuth (Bi) in zinc blende (ZB) phase Indium Arsenide (InAs) is performed taking the full-potential linearized augmented plane wave (FPLAPW) basis sets, the Perdew-Burke-Ernzerh of generalized gradient approximation (PBEsol) exchange correlation (XC) functional, Modified Becke-Johnson (mBJ) potential in the density functional theory (DFT) computation and valence band anticrossing (VBAC) model. Comparatively larger atomic sized Bi impurity in InAs leads to increment in the lattice constant, non-linear reduction of bulk modulus, decrease the bandgap by 31.17 meV/Bi%, and increase the spin-orbit coupling splitting energy (ΔSO) by 18.35 meV/Bi%. A consistent redshift in the optical spectra towards the > 3 μm region is observed for increasing Bi concentration, which makes InAs1-xBix a suitable candidate for the atmospheric infrared transmission windows at 3–5 and 8–12 μm. A reasonably higher value ofΔSOcompared to the direct bandgap mitigate the Auger like non-radiative recombination losses in LASERs and Photodetectors. Computed thermoelectric properties like Seebeck coefficient and electrical conductivity reflects the superiority of Bi incorporation in InAs. Nevertheless, Bi impurity leads to reduction in carrier effective mass in InAs1-xBix, which opens up the possibility to utilize it in High Electron Mobility Transistors (HEMTs) devices.

Valence band engineering of GaAsBi for low noise avalanche photodiodes

Avalanche Photodiodes (APDs) are key semiconductor components that amplify weak optical signals via the impact ionization process, but this process’ stochastic nature introduces ‘excess’ noise, limiting the useful signal to noise ratio (or sensitivity) that is practically achievable. The APD material’s electron and hole ionization coefficients (α and β respectively) are critical parameters in this regard, with very disparate values of α and β necessary to minimize this excess noise. Here, the analysis of thirteen complementary p-i-n/n-i-p diodes shows that alloying GaAs with ≤ 5.1 % Bi dramatically reduces β while leaving α virtually unchanged—enabling a 2 to 100-fold enhancement of the GaAs α/β ratio while extending the wavelength beyond 1.1 µm. Such a dramatic change in only β is unseen in any other dilute alloy and is attributed to the Bi-induced increase of the spin-orbit splitting energy (∆so). Valence band engineering in this way offers an attractive route to enable low noise semiconductor APDs to be developed.

Strain-induced splitting in valence band of Si–Ge whiskers

The temperature dependences of resistance for the p-type conductivity solid solution silicon–germanium whiskers doped by boron with concentration of 1 × 1018 cm−3 were investigated in the temperature range of 4.2–300 K and under the uniaxial compressive strain till − 3 × 10–3 rel. un. We studied the strain influence, which was caused on a spin–orbit splitting in the valence band spectrum. As an outcome, the spin–orbit splitting energies for both light and heavy holes were discovered based on the k–p method. The strain-induced effects of solid solution Si0.2Ge0.8 whiskers were studied at low temperatures. Found giant piezoresistive effect at helium temperature gives opportunity to create the supersensitive strain gages on the basis of silicon–germanium whiskers with doping concentration in the vicinity to the metal–insulator transition. The mechanical sensor operating at helium temperature and deformation range of 5 × 10–4–1.3 × 10–3 rel. un. was designed with the sensitive element Si0.2Ge0.8 whiskers doped to concentration 1 × 1018 cm−3.

Band gap energy of the As-rich InxGa1-xBiyAs1-y depending on composition

A model estimating the band gap energy of the As-rich InxGa1-xBiyAs1-y is set up. An excellent description is shown. It is found that the In and Bi fractions do not modify the Г valence band maximum (VBM) independently. However, they modify the Г conduction band minimum (CBM) independently. The incorporation of the In fraction in the GaBiyAs1-y alloy will lead to the coupling interaction between the Bi level and the Г CBM of the host material decreasing. It is due to that the energy difference between the Bi level and the Г VBM of InxGa1-xAs enlarges with increasing In fraction. InxGa1-xBiyAs1-y needs less Bi fraction than GaBiyAs1-y when the spin–orbit splitting energy surpasses the band gap energy. The reason is that incorporating In fraction in GaBiyAs1-y can reduce the band gap energy while the spin–orbit splitting energy almost keeps a constant. In addition, the impurity-host interaction depends on not only the impurity anion fraction, but also the host anion fraction when the impurity anion fraction reaches a certain degree. If there are two or more cations in the alloy, the coupling parameter depending on the cation fraction should be taken into consideration. Based on the existing evidence, it can be concluded that InxGa1-xBiyAs1-y has a direct band gap in the whole composition range.

Impact of spin-orbit splitting on two-photon absorption spectra in a halide perovskite single crystal

Metal halide perovskites have emerged as versatile photonic device materials because of their outstanding optical properties. Here, we report the two-photon absorption (TPA) spectra for $\mathrm{C}{\mathrm{H}}_{3}\mathrm{N}{\mathrm{H}}_{3}\mathrm{Pb}{\mathrm{Br}}_{3}$ perovskite single crystals under linearly and circularly polarized laser pulses. We experimentally determined the spin-orbit splitting energy from the TPA linear-circular dichroism spectrum and found the higher-energy band around 0.8 eV above the band edge. From a theoretical analysis of the experimental data, we evaluated the exciton binding energy and the exciton reduced mass. Our findings provide essential information on the electronic structures and carrier dynamics of halide perovskites.

Polarization dependent photoluminescence and optical anisotropy in CuPtB-ordered dilute GaAs1–xBix alloys

The GaAs1–xBix semiconductor alloy allows one to achieve large bandgap reduction and enhanced spin–orbit splitting energy at dilute Bi quantities. The bismide is currently being developed for near- to mid-infrared lasers, multi-junction solar cells, and photodetectors. In this structure–property relationship study of GaAsBi alloys, we report polarization dependent photoluminescence that reaches a polarization ratio up to 2.4 at room temperature. Polarization dependence is also presented using transmittance spectra, birefringence, and linear dichroism. The optical anisotropy observations agree with the predictions of point symmetry reduction in the CuPtB-type ordered GaAsBi phase. The structural ordering is investigated experimentally from the atomic scale in molecular-beam epitaxy (MBE) grown samples on exact and miscut (001) GaAs substrates, as well as on (001) Ge. The latter sample is composed of anti-phase domains in which the ordering axes are rotated by 90° angles. Since the conditions stabilizing the CuPtB ordered phase fall within the typical MBE growth regime of dilute bismides, the optical anisotropy in GaAsBi alloys is expected to be ubiquitous. These findings are important for the future development of GaAsBi-based optoelectronics and also provide new means to analyze structurally complex bismide alloys.

Origin of luminescence in Bi3+ - doped lanthanide niobates

Photoluminescence characteristics of the undoped and Bi3+-doped lanthanide niobates are investigated by the steady-state and time-resolved spectroscopy methods in a wide temperature range of 4.2–500 K. The broad visible emission bands with the large Stokes shifts are found to arise from the triplet relaxed excited states characterized by a small (∼1 meV) spin-orbit splitting energy. This indicates the exciton-like origin of all the observed emission bands. The data allow to conclude that the Bi3+-related triplet relaxed excited state is located inside the conduction band. No ultraviolet emission caused by the radiative decay of the triplet relaxed excited state of a Bi3+ ion is observed. The dependences of the emission intensity on the Bi3+ content indicate that the complex visible emission band of the Bi3+-doped niobates consists of two main, the higher-energy and the lower-energy, components arising from the excitons localized around the single Bi3+ ions and the {Bi3+ - Bi3+} dimers, respectively. The processes resulting in the appearance of the exciton-like emission under photoexcitation in the Bi3+-related absorption bands are discussed.