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Optical absorption via intersubband transition of electrons in GaAs/Al <sub/>x</sub> Ga <sub/>1?x</sub> As multi-quantum wells in an electric field
摘要： Based on the effective mass approximation, the Schr?dinger equation and Poisson equation in GaAs/AlxGa1?xAs multi-quantum wells (MQWs) are self-consistently solved to obtain the wave functions and energy levels of electrons in the conduction band for the ground first excited state by considering a lateral electric field (LEF). Then, the effects of size, ternary mixed crystal, doping concentration, and temperature on linear and nonlinear intersubband optical absorption coefficients (IOACs), and refractive index changes (RICs) due to the transition between ground states and the first excited states of electrons are discussed based on Fermi’s golden rule. The results show that, under a fixed LEF, with increase of Al composition and doping concentration, the IOACs produce a red shift. With increases of both widths of the wells and barriers IOACs appear as blue shifts and their amplitudes increase, but the barrier width change is much more important to affect nonlinear IOACs, whereas increasing the temperature results in a blue shift first and then a red shift of IOACs. When the other parameters are fixed but there is an increase in the LEF, IOACs occur with a blue shift, and the RICs have similar properties.
关键词： multi-quantum wells,optical absorption of electronic intersubband transition,refractive index changes,lateral electric field
更新于2025-09-23 15:22:29
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Direct observation of cross-polarized excitons in aligned single-chirality single-wall carbon nanotubes
摘要： Optical properties of single-wall carbon nanotubes (SWCNTs) for light polarized parallel to the nanotube axis have been studied extensively, whereas their response to light polarized perpendicular to the nanotube axis has not been well explored. Here, by using a macroscopic film of highly aligned single-chirality (6,5) SWCNTs, we performed a systematic polarization-dependent optical absorption spectroscopy study. In addition to the commonly observed angular-momentum-conserving interband absorption of parallel-polarized light, which generates E11 and E22 excitons, we observed a small but unambiguous absorption peak whose intensity is maximum for perpendicular-polarized light. We attribute this feature to the lowest-energy cross-polarized interband absorption processes that change the angular momentum along the nanotube axis by ±1, generating E12 and E21 excitons. Unlike previous observations of cross-polarized excitons in polarization-dependent photoluminescence and circular dichroism spectroscopy experiments, our direct observation using absorption spectroscopy allowed us to quantitatively analyze this resonance. Specifically, we determined the energy and oscillator strength of this resonance to be 1.54 and 0.05, respectively, compared with the values for the E11 exciton peak. These values, in combination with a comparison with theoretical calculations, in turn led to an assessment of the environmental effect on the strength of Coulomb interactions in this aligned single-chirality SWCNT film.
关键词： polarization-dependent,single-wall carbon nanotubes,cross-polarized excitons,aligned film,optical absorption spectroscopy,Coulomb interactions
更新于2025-09-23 15:22:29
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Effects of inter-subband couplings on bound and extended states of terahertz cascade structures
摘要： We theoretically analyze the effect of inter-subband couplings on the eigenstates of a terahertz heterostructure in the presence of coulombic donors. We find that the inter-subband electron-donor interaction causes a drastic reorganization of the eigenenergies and a strong admixture between the subbands that decisively influences the optical absorption spectrum of the structure. These results illustrate the importance of the inter-subband couplings in the formulation of the eigenstates of imperfect terahertz heterostructures.
关键词： inter-subband couplings,eigenstates,terahertz cascade structures,optical absorption spectrum
更新于2025-09-23 15:21:21
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Manipulating Optical Absorption of Indium Selenide Using Plasmonic Nanoparticles
摘要： In this work, we propose using periodic Au nanoparticles (NPs) in indium selenide-based optoelectronic devices to tune the optical absorption of indium selenide. Electromagnetic simulations show that optical absorption of indium selenide can be manipulated by tuning plasmonic resonance. The e?ect on the plasmonic resonance of the size, period of NPs, the thickness of silicon oxide, and the insulator spacer is systematically analyzed. A high absorption enhancement over the visible spectrum is achieved through systematic optimization of nanostructures.
关键词： optoelectronic devices,indium selenide,optical absorption,plasmonic nanoparticles,plasmonic resonance
更新于2025-09-23 15:21:01
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Crystal growth and spectroscopic investigations of Dy:YAlO3 and Dy,Tm:YAlO3 crystals for a??3a?ˉ??m laser application
摘要： Dy3+:YAP and Dy3+,Tm3+:YAP single crystals have been successfully synthesized by Czochralski (CZ) method aiming for ~3 μm emission. The optical absorption and emission features of both crystals were studied in detail. A narrow and weak absorption band around 800 nm as well as an upconversion emission under the excitation of 802 nm in Dy3+:YAP crystal along with a weak ~3 μm emission were observed, indicating that Dy3+:YAP crystal is not suitable for direct pumping under 800 nm excitation. Tm3+ ion was introduced as a sensitizer for enhancing ~3 μm emission and found that co-doping with Tm3+ greatly improved the absorption capacity around 800 nm. An enhanced ~3 μm emission was observed in Dy3+,Tm3+:YAP crystal under 795 nm excitation. The energy transfer mechanisms between Dy3+ and Tm3+ ions and the energy transfer micro-parameters were discussed. Higher values of microscopic energy transfer constants between Dy3+ and Tm3+ ions were obtained, proving Tm3+ ion act as an effective sensitizer for Dy3+ ion in YAP crystal. Following the obtained optical results, Dy3+,Tm3+:YAP crystal could be a promising medium for 3 μm laser operation under 795 nm laser diode for practical applications.
关键词： optical absorption,energy transfer micro-parameters,3 μm emission,MIR laser,Dy3+,Tm3+:YAP crystal
更新于2025-09-23 15:21:01
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Effect of Uncontrollable Impurities on the Absorption Spectrum of a NaGd(WO4)2 Laser Crystal
摘要： Three NaGd(WO4)2 single crystals were grown by the Czochralski method using charges of different chemical purity. The impurity compositions of the grown crystals were analyzed by inductively coupled plasma mass spectrometry. The optical absorption spectra of the crystals were measured, and the effect of uncontrollable impurities on their optical properties and color was analyzed. The green color encountered in NaGd(WO4)2 crystals in some cases was shown to be due to the uncontrollable impurities of d elements, among which the chromium impurity had the most significant effect.
关键词： optical absorption,impurity purity,color centers,single crystals,zinc tungstate,ytterbium
更新于2025-09-23 15:21:01
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Facile synthesis of Cr doped hierarchical ZnO nano-structures for enhanced photovoltaic performance
摘要： Transition metal doped ZnO has been widely used in various research areas such as optoelectronics, chemical sensors, solar cells and photo catalysts. Herein, we fabricated Cr-doped ZnO nanospheres by a facile solvothermal treatment for enhanced photovoltaic performance. A systematic study of the structural and optical properties of Cr doped ZnO were investigated by scanning electron microscopy (SEM), X-ray diffraction technique (XRD), Ultra violet-Visible spectroscopy (UV–Vis) respectively. XRD patterns confirm that the samples have hexagonal (wurtzite) structure with no additional peaks, which suggests that Cr ions replaces the regular Zn sites in the ZnO crystal structure. Furthermore, doped ZnO nanospheres were employed in the hybrid solar cells in combination with P3HT and gave better current densities than their corresponding undoped counterparts. The increase in solar cell efficiency of doped ZnO nanospheres is solely due to the improvement in the charge separation efficiency in the 4% Cr doped ZnO nanospheres. Optoelectronic analysis of the Cr doped ZnO hybrid solar cell showed comparable results of JSC ?3.7 (mAcm?2), VOC 0.44 (V), Fill Factor 0.49 and Efficiency (?) 0.79 (%). The enhanced photovoltaic activity of the Cr doped hierarchical ZnO nanostructures provides an interesting grounds for the design and enhancement of the low cost, feasible synthesis of photovoltaic nanostructure materials.
关键词： Hybrid solar cell,Solvothermal method,Optical absorption,Photovoltaic device,Nanostructure
更新于2025-09-23 15:21:01
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Amorphous Silicon with Extremely Low Absorption: Beating Thermal Noise in Gravitational Astronomy
摘要： Amorphous silicon has ideal properties for many applications in fundamental research and industry. However, the optical absorption is often unacceptably high, particularly for gravitational-wave detection. We report a novel ion-beam deposition method for fabricating amorphous silicon with unprecedentedly low unpaired electron-spin density and optical absorption, the spin limit on absorption being surpassed for the first time. At low unpaired electron density, the absorption is no longer correlated with electron spins, but with the electronic mobility gap. Compared to standard ion-beam deposition, the absorption at 1550 nm is lower by a factor of ≈100. This breakthrough shows that amorphous silicon could be exploited as an extreme performance optical coating in near-infrared applications, and it represents an important proof of concept for future gravitational-wave detectors.
关键词： amorphous silicon,thermal noise,gravitational-wave detection,ion-beam deposition,optical absorption
更新于2025-09-23 15:21:01
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Note: Complementary approach for radiation dosimetry with Ag <sup>+</sup> -activated phosphate glass
摘要： Silver ion-activated phosphate glass (Ag+-glass) has a good potential for application to radiation dosimetry in various radiation fields due to its multifunctional properties as a detector. The Ag+-glass provides three independent signals of radiophotoluminescence, optical absorption, and nuclear track. The combination of these signals allows the dynamic range of the measured dose (10 μGy–10 kGy) and linear energy transfer (<10 keV/μm and >1 MeV/μm) to be widened.
关键词： optical absorption,radiophotoluminescence,Ag+-activated phosphate glass,radiation dosimetry,nuclear track
更新于2025-09-23 15:21:01
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Many-particle excitations in non-covalently doped single-walled carbon nanotubes
摘要： Doping of single-walled carbon nanotubes leads to the formation of new energy levels which are able to participate in optical processes. Here, we investigate (6,5)-single walled carbon nanotubes doped in a solution of hydrochloric acid using optical absorption, photoluminescence, and pump-probe transient absorption techniques. We find that, beyond a certain level of doping, the optical spectra of such nanotubes exhibit the spectral features related to two doping-induced levels, which we assign to a localized exciton X and a trion T, appearing in addition to an ordinary exciton E1. We evaluate the formation and relaxation kinetics of respective states and demonstrate that the kinetics difference between E1 and X energy levels perfectly matches the kinetics of the state T. This original finding evidences the formation of trions through nonradiative relaxation via the X level, rather than via a direct optical excitation from the ground energy state of nanotubes.
关键词： exciton,doping,optical absorption,pump-probe transient absorption,photoluminescence,trion,single-walled carbon nanotubes
更新于2025-09-23 15:19:57