Intraband Energy Research Articles

Self–Trapped Exciton versus Band–Edge Electron Transitions: Insights of the Factors Affecting the Optical Properties of Lead–Free Sn–Halide Perovskites

AbstractLead–free Sn–halide perovskites (Sn–HPs) are attractive photomaterials due to their lower toxicity, and some of them with higher stability against moisture and water, compared to their Pb‐based analogous. Interestingly, Sn‐HPs can exhibit two types of optical characteristics: the first scenario is known as band‐edge electron transitions [or band‐to‐band (b‐b) emission], where accumulated electrons in the conduction band recombine with holes in the valence band, providing a close separation between the absorption edge/photoluminescence (PL) peak (small Stokes shift). The second scenario is denominated as self‐trapped exciton (STE), where intraband gap energy states are formed to trap photocarriers generated in the perovskite, producing a broadband PL and a large Stokes shift. These optical features have been suitable for developing prominent devices, but there is no consolidated explanation about the key factors influencing the emergence of b–b emission or STE in Sn‐HPs, mainly the presence of these PL mechanisms in a particular perovskite system. This review highlights how the chemical composition, structural defects, and synthetic procedures are pivotal to producing Sn‐HPs with specific b–b or STE features. This will allow the preparation of Sn‐HPs with better quality/stability, and facile modulation of their PL properties, expanding their future applicability in LCD technologies.

Molecularly Imprinted Viral Protein Integrated Zn-Cu-In-Se-P Quantum Dots Superlattice for Quantitative Ratiometric Electrochemical Detection of SARS-CoV-2 Spike Protein in Saliva.

Solution-processable colloidal quantum dots (QDs) are promising materials for the development of rapid and low-cost, next-generation quantum-sensing diagnostic systems. In this study, we report on the synthesis of multinary Zn-Cu-In-Se-P (ZCISeP) QDs and the application of the QDs-modified electrode (QDs/SPCE) as a solid superlattice transducer interface for the ratiometric electrochemical detection of the SARS-CoV-2-S1 protein in saliva. The ZCISeP QDs were synthesized through the formation of In(Zn)PSe QDs from InP QDs, followed by the incorporation of Cu cations into the crystal lattice via cation exchange processes. A viral-protein-imprinted polymer film was deposited onto the QDs/SPCE for the specific binding of SARS-CoV-2. Molecular imprinting of the virus protein was achieved using a surface imprinting electropolymerization strategy to create the MIP@QDs/SPCE nanosensor. Characterization through spectroscopic, microscopic, and electrochemical techniques confirmed the structural properties and electronic-band state of the ZCISeP QDs. Cyclic voltammetry studies of the QDs/SPCE superlattice confirmed efficient electron transport properties and revealed an intraband gap energy state with redox peaks attributed to the Cu1+/2+ defects. Binding of SARS-CoV-2-S1 to the MIP@QDs/SPCE cavities induced a gating effect that modulated the Fe(CN)6 3-/4- and Cu1+/2+ redox processes at the nanosensor interface, producing dual off/on ratiometric electrical current signals. Under optimal assay conditions, the nanosensor exhibited a wide linear detection range (0.001-100 pg/mL) and a low detection limit (0.34 pg/mL, 4.6 fM) for quantitative detection of SARS-CoV-2-S1 in saliva. The MIP@QDs/SPCE nanosensor demonstrated excellent selectivity against nonspecific protein targets, and the integration with a smartphone-based potentiostat confirmed the potential for point-of-care applications.

Description of moment of inertia and the interplay between anti-pairing and pairing correlations in 244Pu and 248Cm* *Xiao-Tao He Supported by the the National Key R and D Program of China (2023YFA1606503)

A variable moment of inertia (VMI) inspired interacting boson model (IBM), which includes many-body interactions and a perturbation possessing (5) (or (5)) symmetry, is used to investigate the rotational bands of the mass region. A novel modification is introduced, extending the Arima coefficient to the third order. This study is dedicated to the quantitative analysis of evolving trends in intraband γ-transition energy as well as the kinematic and dynamic moments of inertia (MoIs) within the rotational bands of Pu and Cm. The computed outcomes exhibit an exceptional degree of agreement with experimental observations across various conditions. The significance of including a higher-order Arima coefficient is further examined by contrasting it with the previously proposed model. The calculated results demonstrate the significance of both the anti-pairing and pairing effects in the evolution of the dynamic MoI. Additionally, these insights reveal the importance of a newly introduced parameter in accurately depicting complex nuclear behaviors, such as back-bending, up-bending, and downturn in the MoI.

Potential enhancements in the photocatalytic activity of the anatase 001 surface by adding cerium impurity

AbstractThis research investigates the structural and electronic properties of titanium dioxide ($$ TiO_2 $$ T i O 2 ) surfaces with the addition of cerium (Ce) impurities using first principles calculations within the framework of density functional theory, employing the pseudopotential method and the computational package Quantum ESPRESSO. Density of states (DOS) calculations reveal that the clean surface exhibits semiconductor behavior. In contrast, the titanium dioxide surface with Ce impurities on the fifth layer generates intermediate states within the energy band gap, resulting in a reduction in the band, with an intraband energy gap of 0.7882 eV induced. Moreover, the inclusion of a Ce atom on the fourth layer of the surface results it is observed that the surface an important characteristic is the appearance of intermediate states in the band gap, which are close to the valence band with a magnetic moment of 0.91 $$ \mu \beta /cell $$ μ β / c e l l . The ntraband gap can enhance the utilization of the visible spectrum. Additionally, the Ce impurity on the $$ TiO_2 $$ T i O 2 surface could promote greater photocatalytic activity in pollutant degradation and increase the oxidative capacity of titanium dioxide.

Weakly confined silicon nanodiscs as material system for THz absorption: analytical study

A weakly confined silicon based nano structure as a THz absorbing material is introduced. Using an effective mass approximation and 2D hydrogenic solution along with 1st order perturbation correction for truncated potential, we calculated inter-band and intra-band energy spectrum of weakly confined silicon nanodisc system. Variation of inter-band and intra-conduction-band absorption spectrum with the different sizes of the nanodisc are presented for various diameter from 10 nm to 32 nm and constant thickness of 4 nm. Inter-band and intra-band absorption spectrum are simulated using the oscillator strength. These calculation shows that intra-band absorption spectrum of the weakly confined nanodisc can cover a large THz (∼ 0.3–6.5 THz) spectrum range for these set of nanodiscs. The proposed silicon based THz absorbing material can be utilized for CMOS compatible THz technology if design on silicon-on-insulator system.

Enhancement of Spontaneous Photon Emission in Inverse Photoemission Transitions in Semiconductor Quantum Dots.

Inverse photoemission (IPE) is a radiative electron capture process where an electron is transiently captured in the conduction band (CB) followed by intraband de-excitation and spontaneous photon emission. IPE in quantum dots (QDs) bypasses optical selection rules for populating the CB and provides insights into the capacity for electron capture in the CB, the propensity for spontaneous photon emission, intraband transition energies where both initial and final states are in the CB, and the generation of photons with frequencies lower than the bandgap. Here, we demonstrate using time-dependent perturbation theory that judicious application of electric fields can significantly enhance the IPE transition in QDs. For a series of CdSe, CdS, PbSe, and PbS QDs, we present evidence of field-induced enhancement of IPE intensities (188% for Cd54Se54), field-dependent control of emitted photon frequencies (Δω = 0.73 eV for Cd54Se54), and enhancement of light-matter interaction using directed Stark fields (103% for Cd54Se54).

Tuning electrical and optical properties of InAs/GaAs1−x Sb x quantum dots

Understanding the electrical and optical properties of InAs/GaAs(Sb) quantum dots (QDs) is essential for designing and improving the performance of related semiconductor QD devices. In this paper, the effects of In segregation, QD size, capping layer thickness and Sb composition on the electrical and optical properties of type I and type II InAs/GaAs1−x Sb x () QDs are systematically investigated and general regularities are summarized. The comparisons of electron distribution probabilities, interband and intraband transition energies and absorption coefficients show that In segregation and QD size have a strong influence on the electron energy level positions of InAs QDs and that the trade-offs between absorption peak energy, absorption intensity and radiative lifetime of InAs/GaAs1−x Sb x QDs can be optimized by adjusting the thickness and Sb composition of the GaAs1−x Sb x capping layer. The results obtained are promising for the applications in the pre-design and performance feedback of the QD devices such as QD lasers, QD infrared detectors and intermediate band solar cells.

Effects of High Pressure on the Bandgap and the d–d Crystal Field Transitions in Wolframite NiWO4

The pressure effects on the optical and structural properties of NiWO4 have been studied experimentally and theoretically. The fundamental bandgap decreases with a pressure coefficient of −12.0 ± 0.2 meV/GPa. Meanwhile, the Ni2+ d–d transition energies increase at a rate of 7.4–14.8 meV/GPa. Therefore, the energy differences between the fundamental band and the Ni2+ d–d transition bands gradually decrease under pressure, which is beneficial to improve its optical performance. These optical phenomena are associated with structural variations. The shrinkage of the WO6 octahedron enhances the hybridization between the W 5d and O 2p orbitals, resulting in bandgap reduction. The pressure-induced enhancement of the NiO6 octahedral symmetry increases the crystal field splitting, thereby yielding increases in the Ni2+ d–d intraband transition energies. Besides, a pressure-induced structural phase transition is also observed around 20.0 GPa by both angle-dispersive synchrotron X-ray diffraction (ADXRD) and Raman experiments. This study provides valuable insight into the electron–lattice coupling of NiWO4 under compression and an effective way to modulate the electronic structure and optical properties of isomorphic wolframite materials.

Green Light Photoelectrocatalysis with Sulfur-Doped Carbon Nitride: Using Triazole-Purpald for Enhanced Benzylamine Oxidation and Oxygen Evolution Reactions.

Materials dictate carbon neutralindustrialchemicalprocesses. Visible-light photoelectrocatalysts from abundant resources will play a key role in exploiting solar irradiation. Anionic doping via pre-organization of precursors and further co-polymerization creates tuneable semiconductors. Triazole derivative-purpald, an unexplored precursor with sulfur (S) container, combined in different initial ratios with melamine during one solid-state polycondensation with two thermal steps yields hybrid S-doped carbon nitrides (C3 N4 ). The series of S-doped/C3 N4 -based materials show enhanced optical, electronic, structural, textural, and morphological properties and exhibit higher performance in organic benzylamine photooxidation, oxygen evolution, and similar energy storage (capacitor brief investigation). 50M-50P exhibits the highest photooxidation conversion (84±3%) of benzylamine to imine at 535nm - green light for 48h, due to a discrete shoulder (≈700)nm, high sulfur content, preservation of crystal size, new intraband energy states, structural defects by layer distortion, and 10-16nm pores with arbitrary depth. This work innovates by studying the concomitant relationships between: 1) the precursor decomposition while C3 N4 is formed, 2) the insertion of Simpurities, 3) the S-doped C3 N4 property-activity relationships, and 4) combinatorial surface, bulk, structural, optical, and electronic characterization analysis. This work contributes to the development of disordered long-visible-lightphotocatalysts for solar energy conversion and storage.

Intraband Transitions of Nanocrystals Transforming from Lead Selenide to Self-doped Silver Selenide Quantum Dots by Cation Exchange.

In search of heavy metal-free mid-IR active colloidal materials, self-doped silver selenide colloidal quantum dots (CQDs) can be an alternative offering tunable mid-IR wavelength with a narrow bandwidth. One of the challenges in the study of the intraband transition is developing a method to widen the intraband transition energy range as well as reducing the toxicity of the materials. Here, we present AgxSe (x > 2) CQDs exhibiting an intraband transition up to 0.39 eV, produced by the cation exchange (CE) method from PbSe CQDs. The major electronic transition efficiently changes from the SWIR band gap of PbSe CQDs to the mid-IR intraband transition of the AgxSe CQDs by the CE. The intraband exciton is verified by examining the absorption and emission of the CE AgxSe CQDs as well as their applications on electrochemical mid-IR luminescence and mid-IR intraband photodetectors.

Effect of Ring Radius and Electric Field on the Relative Refractive Index of a GaAs Quantum Ring

The influence of inner ring radius and in-plane electric field on the relative refractive index of a GaAs-AlGaAs single circular quantum ring is theoretically studied. The energy levels and corresponding wave functions are obtained by solving the Schrödinger equation within effective mass and envelope wave function approximations. The changes in the intraband transition energies are presented in terms of varying ring radius and external electric fields. Relative refractive index changes are calculated through the compact-density matrix approach. The results show that both ring radius and electric field significantly affect the location and also the peak intensities of relative refractive index changes on the incident photon energy.

Efficiency Study of PbTe/CdTe Core/Shell Quantum Dots Solar Cells

In this work we theoretically study how to optimize the efficiency of an intermediate band solar cell based on IV-VI PbTe/CdTe semiconductor materials. We focus our attention on how control structural parameters, such as the height and radius in cylindrical quantum dots and the radius in spherical quantum dots to obtain the inter and intraband transition energies that provide the highest efficiency values of the solar cell. The calculation of the energy levels, the selection rules for transitions energies were performed using the 4×4 k.p Kane-Dimmok Hamiltonian.

Ultrafast intraband Auger process in self-doped colloidal quantum dots

Summary Investigating the separate dynamics of electrons and holes has been challenging, although it is critical for the fundamental understanding of semiconducting nanomaterials. n-Type self-doped colloidal quantum dots (CQDs) with excess electrons occupying the low-lying state in the conduction band (CB) have attracted a great deal of attention because of not only their potential applications to infrared optoelectronics but also their intrinsic system that offers a platform for investigating electron dynamics without elusive contributions from holes in the valence band. Here, we show an unprecedented ultrafast intraband Auger process, electron relaxation between spin-orbit coupling states, and exciton-to-ligand vibrational energy transfer process that all occur exclusively in the CB of the self-doped β-HgS CQDs. The electron dynamics obtained by femtosecond mid-infrared spectroscopy will pave the way for further understanding of the blinking phenomenon, disproportionate charging in light-emitting diodes, and hot electron dynamics in higher quantum states coupled to surface states of CQDs.

Size- and Temperature-Dependent Intraband Optical Properties of Heavily n-Doped PbS Colloidal Quantum Dot Solid-State Films.

Steady-state access to intraband transitions in colloidal quantum dots (CQDs), via doping, permits exploitation of the electromagnetic spectrum at energies below the band gap. CQD intraband optoelectronics allows envisaging cheap mid- and long-wavelength infrared photodetectors and light-emitting devices, which today employ epitaxial materials. As intraband devices start to emerge, thorough studies of the basic properties of intraband transitions in different CQD materials are needed to guide technological research. In this work, we investigate the size and temperature dependence of the intraband transition in heavily n-doped PbS quantum dot (QD) films. In the studied QD size range (5-8 nm), the intraband energy spans from 209 to 151 meV. We measure the intraband absorption coefficient of heavily doped PbS QD films to be around 2 × 104 cm-1, proving that intraband absorption is as strong as interband absorption. We demonstrate a negative dependence of the intraband energy with temperature, in contrast to the positive dependence of the interband transition. Also opposite to the interband case, the temperature dependence of the intraband energy increases with decreasing size, going from -29 μeV/K to -49 μeV/K in the studied size range.

Linear and third order nonlinear optical properties of GaAs quantum dot in terahertz region

Abstract We study the electronic and optical properties of GaAs quantum dot embedded in Ga1-yAlyAs matrix. Using the effective mass approximation with the finite confinement potential the intraband energy levels and the wavefunctions are obtained. The linear and third order nonlinear optical properties, photoabsorption coefficient, refractive index change and susceptibility are studied for different dot radius in the terahertz region.

Theory of the strongly nonlinear electrodynamic response of graphene: A hot electron model

An electrodynamic response of graphene to a strong electromagnetic radiation is considered. A hot electron model (HEM) is introduced and a corresponding system of nonlinear equations is formulated. Solutions of this system are found and discussed in detail for intrinsic and doped graphene: the hot electron temperature, non-equilibrium electron and holes densities, absorption coefficient and other physical quantities are calculated as functions of the incident wave frequency $\omega$ and intensity $I$, of the equilibrium chemical potential $\mu_0$ and temperature $T_0$, scattering parameters, as well as of the ratio $\tau_\epsilon/\tau_{\rm rec}$ of the intra-band energy relaxation time $\tau_\epsilon$ to the recombination time $\tau_{\rm rec}$. The influence of the radiation intensity on the absorption coefficient $A$ at low ($\hbar\omega\lesssim 2|\mu_0|$, $dA/dI>0$) and high ($\hbar\omega\gtrsim 2|\mu_0|$, $dA/dI<0$) frequencies is studied. The results are shown to be in good agreement with recent experimental data.

Carrier heating and its effects on the current-voltage relations of conventional and hot-carrier solar cells: A physical model incorporating energy transfer between carriers, photons, and phonons

Theoretical models and frameworks are developed to investigate the effects of carrier heating on conventional and hot-carrier solar cells. They incorporate intraband carrier energy relaxation into the Shockley-Queisser model for conventional solar cells and the Ross-Nozik model for hot-carrier solar cells. Explicit formulas are presented to calculate intraband carrier energy relaxation rates via the interactions of polar longitudinal optical phonons and deformation-potential longitudinal and transverse optical phonons. These formulas incorporate the decay processes and phonon bath sharing of optical phonons. The effects of carrier heating on the current-voltage characteristics of conventional and hot-carrier solar cells are investigated and discussed for GaAs, InP, GaSb, and InAs materials. This paper will particularly discuss the differences between extraction cooling in hot-carrier solar cells and recombination heating from stimulated photon emissions in semiconductor lasers. It will prove that carriers in hot-carrier solar cells need to be extracted with a selective-contact energy larger than their quasi-Fermi-level separation in order to make devices work with extraction cooling, rather than recombination heating.

Empirical evidence of a superrigid structure of “flat” superdeformed bands

For the first time, we present the empirical evidence of superrigid character of the ``flat'' superdeformed bands in the Tl and Pb isotopes. For this purpose, we have used various rotational energy formulas. The free parameters of superdeformed (SD) bands in the Tl and Pb isotopes have been extracted and systematically studied to obtain the proposed empirical evidence. In particular, the intraband transition energies of the SD bands have been split into rotational and shape fluctuation energies. The role of the vibrational factor in the evolution of dynamic moment of inertia, softness parameter, alignment, and effective pairing gap parameter of the flat SD bands has been studied. Using these models, two distinct natures have been identified for the SD bands in the Tl and Pb isotopes. Our study establishes the role of shape fluctuations, vibrational effect, deformation, and pairing correlations for the unusual behavior of the dynamic moment of inertia in the flat SD bands of the $A\ensuremath{\approx}190$ mass region.

Magnetic field effects on intraband transitions in elliptically polarized laser-dressed quantum rings

The combined influence of externally applied magnetic and non-resonant intense laser fields (ILF) on the electronic states of GaAs-based two-dimensional circular quantum rings is investigated. The behavior of the electron energy levels as a result of the variation in the strength of the external fields is studied. In particular, the effects of changing the polarization of the intense laser radiation on the conduction band potential profile and allowed energy levels are discussed in detail. The intraband transition energies and the dipole matrix elements are analyzed as functions of the applied magnetic field intensity for different combinations of the intense laser field and resonant probe laser radiation polarizations. The findings can be summarized as follows: i) the quantized energies steadily increase as functions of the magnetic field and ILF-effects, ii) the electric dipole matrix elements are larger for the case of circular non-resonant ILF-polarization and circular laser probe polarization with respect to the case of linear polarized radiation, and iii) the dipole matrix elements have oscillatory behavior due to the complex nature of the wave functions which stems from the imaginary term appearing in the Hamiltonian when magnetic field effects are included.

Interband and intersubband optical transition energies in a Ga0.7In0.3N/GaN quantum dot

Binding energies of a hydrogenic donor impurity and an exciton are investigated in a Ga0.7In0.3N/GaN parabolic quantum dot taking into consideration of spatial confinement effects and the magnetic and electric fields. The strain effects and the built-in internal fields which are related to the piezoelectricity and spontaneous polarization are inserted in the Hamiltonian of the system. Numerical calculations on electronic and optical properties are performed using variational formulism and the density matrix approach. The diamagnetic shift is obtained taking into the account the geometrical confinement effect of the dot. The magnetic and electric fields dependent interband and intraband optical transition energies are obtained in the strong and weak confinement effects. Their corresponding oscillator strengths as functions of magnetic and electric fields are investigated. The optical absorption coefficients due to intersubband and interband transitions with the photon energy are obtained. The results show that the energy shift is much influenced with the inclusion of external perturbations. Specifically, the optical absorption peak undergoes a redshift with the application of electric field whereas it suffers a blue shift when the magnetic field is applied. The results will be helpful for the experimental works on fabricating optical devices such as photodetectors and laser amplifiers using nitride based wide band gap semiconductors.