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Polyoxometalate as Control Agent for the Doping in HgSe Self-Doped Nanocrystals
摘要： Intraband and plasmonic transitions have appeared over the last years as an interesting tool to achieve optical absorption in the mid infrared. Tuning the doping magnitude has become a major challenge not only to tune the optical spectrum but also properties such as the dark current or the time response. Here we investigate the case of self-doped HgSe colloidal quantum dots (CQDs). Tuning of the doping was so far relying on band bending induced by a dipole design at the nanoparticle surface. With such a surface gating approach, it is difficult to conciliate both the massive tuning of the Fermi level with the preservation of transport properties of the CQD arrays. Here we propose a strategy to graft functionalized polyoxometalates (POMs) at the CQD surface and obtain simultaneously a massive tuning of the carrier density (≈5 electrons per nanoparticle) and conduction properties. We bring a consistent demonstration of the HgSe CQD doping decrease by a charge transfer to the POM. This method is highly promising for large tuning of carrier density in degenerately doped semiconductor nanoparticles.
关键词： Intraband,mid infrared,charge transfer,polyoxometalates,plasmonic transitions,doping control,HgSe colloidal quantum dots
更新于2025-09-23 15:21:21
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Self-assembled InAs/InGaAsP/InP quantum dots: Intraband relaxation impacted by ultrathin GaP sublayer
摘要： The influence of an ultrathin GaP (or GaAs) sublayer on the nonradiative intraband relaxation in InAs/InGaAsP/InP quantum dots (QDs) is investigated. It is found that, based on our studies, the QDs with some heights (e.g., 1.5 nm) and GaP sublayer thicknesses (e.g., 1.03 monolayers) present the first excited state (ES) with higher state degeneracy with respect to ground state (GS), which suggests that the Auger relaxation is triggered more easily. We also find that the energy difference of the ES and GS decreases with increasing sublayer thickness, which suggests that the electron–phonon interaction is affected. This work further presents a study of intraband relaxation for an InAs/InP QD with a GaP or GaAs sublayer. It is found that there is a critical thickness of the GaP sublayer: When the sublayer is less than the critical thickness, the intraband relaxation is only determined by one-longitudinal optical (LO) phonon or two-LO phonons, which is dependent on QD heights. However, with the GaAs sublayer, QDs do not have the above feature. This finding may be helpful for designing and optimizing high-speed QD devices.
关键词： quantum dots,electron–phonon interaction,InAs/InGaAsP/InP,intraband relaxation,GaP sublayer
更新于2025-09-23 15:21:01
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Size and Temperature Dependent Intraband Optical Properties of Heavily <i>n-</i> Doped PbS Colloidal Quantum Dot Solid-State Films
摘要： 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 meV 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.
关键词： temperature dependence,absorption coefficient,intraband,lead sulphide,quantum dots
更新于2025-09-23 15:21:01
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Transient optics of gold during laser irradiation: From first principles to experiment
摘要： Intense femtosecond laser pulses can induce dramatic changes on different properties of materials. Laser induced changes of the optical properties are particularly relevant, since they can lead to a modi?cation of the amount of energy that the material absorbs from the laser pulse. In noble metals, changes of re?ectivity upon femtosecond laser illumination are expected to be strong due to the excitation of d electrons. In this work we perform measurements of the re?ectivity of laser excited gold in the infrared and in the ultraviolet range, respectively. We ?nd a remarkable dependence of the re?ectivity on laser ?uence, which is in turn different in both ranges of photon energy. In order to understand the behavior of the re?ectivity in laser excited solids and to explain our measured re?ectivity curves we develop a theoretical scheme in the framework of the two-temperature model with the electronic temperature as the key parameter. Our approach is based on all-electron calculations of the interband contribution to the re?ectivity and a careful determination of the intraband, Drude-like terms and a realistic model for the space and time resolved energy transfer from a Gaussian laser pulse into the electronic system. We obtain very good agreement between experiment and theory and identify the main mechanisms for re?ectivity changes as a function of laser ?uence.
关键词： intraband,Drude-like terms,interband contribution,electronic temperature,Gaussian laser pulse,re?ectivity,two-temperature model,femtosecond laser pulses,optical properties,gold
更新于2025-09-23 15:19:57
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Anti-Stokes Emission from Hot Carriers in Gold Nanorods
摘要： The origin of light emission from plasmonic nanoparticles has been strongly debated lately. It is present as the background of surface enhanced Raman scattering, and, despite the low yield, has been used for novel sensing and imaging application because of its photostability. While the role of surface plasmons as an enhancing antenna is widely accepted, the main controversy regarding the mechanism of the emission is its assignment to either radiative recombination of hot carriers (photoluminescence) or electronic Raman scattering (inelastic light scattering). We have previously interpreted the Stokes shifted emission from gold nanorods as the Purcell effect enhanced radiative recombination of hot carriers. Here we specifically focused on the anti-Stokes emission from single gold nanorods of varying aspect ratios with excitation wavelengths below and above the inter-band transitions threshold while still employing continuous wave lasers. Analysis of the intensity ratios between Stokes and anti-Stokes emission yields temperatures that can only be interpreted as originating from the excited electron distribution and not a thermally equilibrated phonon population despite not using pulsed laser excitation. Consistent with this result as well as previous emission studies using ultrafast lasers, the power-dependence of the upconverted emission is nonlinear and gives the average number of participating photons as a function of emission wavelength. Our findings thus show that hot carriers and photoluminescence play a major role in the upconverted emission.
关键词： surface plasmon resonance,anti-Stokes photoluminescence,interband transition,intraband transition,hot electron temperature,gold nanoparticle
更新于2025-09-19 17:15:36
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Graphene Photonics || Optoelectronic Properties
摘要： In the preceding chapter, the surface optical conductivity eσeωT of graphene contributed by interband transitions was considered, which characterizes the optical response of graphene in the high-frequency region and has a real part given by (3.106) when the relaxation rate is taken to be zero by ignoring the finite relaxation times of the states involved in the transitions. We find by using this surface optical conductivity that monolayer graphene has an approximately constant absorbance of about 2.3 percent in the optical spectral region. However, in the low-frequency region, the surface optical conductivity eσeωT obtained in the preceding chapter is not valid. For example, if we set ω ? 0 for eσe0T to find the DC surface conductivity, we find that eσe0T is also zero, which is inconsistent with the DC surface conductivity obtained in Chapter 2. The discrepancy comes from the fact that eσeωT given in the preceding chapter only accounts for interband absorption of photons with electrons making transitions from a valence band to a conduction band, whereas the DC surface conductivity given in Chapter 2 is solely contributed by the intraband transitions of charge carriers within a valence band or within a conduction band.
关键词： Optoelectronic Properties,Surface Optical Conductivity,Intraband Transitions,Graphene,Interband Transitions
更新于2025-09-16 10:30:52
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The transition from double to single quantum dot induced by THz laser field
摘要： The combined influence of an intense laser field and a homogeneous magnetic field is considered on laterally coupled double quantum dot with isotropic and anisotropic parabolic confinement. It is shown that intense laser field can recover typical properties to a single quantum dot: it creates Fock–Darwin states in a double quantum dot with anisotropic confinement. Also, the laser and the magnetic field effects on the intraband absorption spectrum reveal blueshift if the laser field is increased and redshift with the gain of the magnetic field.
关键词： Double quantum dot,Fock–Darwin states,Intense laser field,Magnetic field,Intraband absorption
更新于2025-09-16 10:30:52
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[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Terahertz Spectroscopy to Unveil Intraband Scattering in Photoexcited Graphene
摘要： Intraband scattering dynamics of optically excited graphene has been explored by using time resolved terahertz spectroscopy. The results for different forms of graphene in terms of layers, Fermi energy position, hydrogen functionalization have been discussed and explained by using Boltzmann transport theory. It is shown how the short-range and Coulomb scattering play important roles in determining photo-induced terahertz conductivity. While photoexcited graphene showed completely negative conductivity (the real part), photoexcited bilayer graphene showed transition from negative to positive in the spectral range 0.5-2.5 THz.
关键词： intraband scattering,Boltzmann transport theory,graphene,terahertz spectroscopy
更新于2025-09-12 10:27:22
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Effective tuning of isotropic and anisotropic properties of quantum dots and rings by external fields
摘要： The combined effects of intense THz laser field, magnetic field and in-plane electric field on electronic states and intraband optical properties of single isotropic quantum dots and rings are investigated using the non-perturbative Floquet theory in the high-frequency limit. Here we show that the change of the electric field direction for fixed values of intense THz laser field parameter can recover the degeneracy of the excited states and the dipole-allowed transition intensities in a quantum dot. Additionally, it is shown that in isotropic quantum rings the intense THz laser and the in-plane electric field create unusual Aharonov-Bohm oscillations. For fixed values of the intense THz laser field parameter, the amplitudes of Aharonov-Bohm oscillations can be effectively tuned by changing the electric field direction. Furthermore, for fixed values of the electric field strength and the laser field parameter the intraband optical properties can be effectively tuned by changing the electric field direction. Therefore, it can be asserted that circular quantum dots or circular rings in the intense THz laser field are equivalent to anisotropic quantum dots or rings respectively, and the electric field direction effectively tunes the single-electron energy spectrum and intraband optical properties of these structures.
关键词： External electric and magnetic fields,Isotropic and unisotropic properties of QDs and QRs,Intraband optical properties of QDs and QRs,Intense THz laser field
更新于2025-09-12 10:27:22
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Plasmonic Hot Hole Transfer in Gold Nanoparticle-decorated Transition Metal Dichalcogenide Nanosheets
摘要： This work studies photogenerated carrier dynamics in gold nanoparticle (AuNP)-decorated mono- to few-layer transition metal dichalcogenide (TMD) nanosheets using transient absorption spectroscopy (TA). TA unveiled the presence of a long-lived photo-induced absorption (PIA) feature in both MoSe2 and WSe2 decorated with covalently bound AuNPs. This long-lived PIA feature emerges only from direct Au interband excitation in AuNP-decorated MoSe2 and WSe2; it does not manifest from intraband excitation nor in AuNP-decorated MoS2 or WS2. Based on x-ray/ultraviolet photoelectron spectroscopy and previous theoretical studies, it is proposed that this PIA signature arises from hot hole transfer from the AuNP to the adjacent TMD, producing a charge-separated state. This suggests charge separation at the metal-semiconductor interface may be used to extend the lifetime of interband excitation generated hot holes. This development could represent an important advance in harnessing plasmonic dissipation pathways to generate long-lived carriers suited for solar-driven light harvesting and catalysis.
关键词： molybdenum diselenide,hot carriers,transient absorption,carrier dynamics,intraband,interband transitions,ultrafast spectroscopy
更新于2025-09-12 10:27:22