Showing papers on "Photoexcitation published in 2007"
TL;DR: It is demonstrated that the intermolecular hydrogen bonds between coumarin 102 (C102) and hydrogen-donating solvents are strengthened in the early time of photoexcitation to the electronically excited state by theoretically monitoring the stretching modes of C=O and H-O groups.
Abstract: To study the early time hydrogen-bonding dynamics of chromophore in hydrogen-donating solvents upon photoexcitation, the infrared spectra of the hydrogen-bonded solute-solvent complexes in electronically excited states have been calculated using the time-dependent density functional theory (TDDFT) method. The hydrogen-bonding dynamics in electronically excited states can be widely monitored by the spectral shifts of some characteristic vibrational modes involved in the formation of hydrogen bonds. In this study, we have demonstrated that the intermolecular hydrogen bonds between coumarin 102 (C102) and hydrogen-donating solvents are strengthened in the early time of photoexcitation to the electronically excited state by theoretically monitoring the stretching modes of C=O and H-O groups. This is significantly contrasted with the ultrafast hydrogen bond cleavage taking place within a 200-fs time scale upon electronic excitation, proposed in many femtosecond time-resolved vibrational spectroscopy experiments. The transient hydrogen bond strengthening behaviors in excited states of chromophores in hydrogen-donating solvents, which we have demonstrated here for the first time, may take place widely in many other systems in solution and are very important to explain the fluorescence-quenching phenomena associated with some radiationless deactivation processes, for example, the ultrafast solute-solvent intermolecular electron transfer and the internal conversion process from the fluorescent state to the ground state.
554 citations
14 Mar 2007
312 citations
272 citations
TL;DR: The temporal spectral evolution relevant to the structural change clearly exhibited an isoemissive point around 675 nm, which manifests that there exists a shallow potential minimum at the perpendicular geometry on the S1 surface, and the S2 state stays undistorted for a finite period as long as 660 fs before the structural distortion.
Abstract: In copper(I) complex [Cu(dmphen)2]+ (dmphen = 2,9-dimethyl-1,10-phenanthroline), a “flattening” structural change is induced with 1MLCT excitation, which is a prototype of the structural change accompanied with Cu(I)/Cu(II) conversion in copper complexes. Femtosecond and picosecond emission dynamics of this complex were investigated in solution at room temperature with optically allowed S2 ← S0 photoexcitation. Time-resolved emission was measured in the whole visible region, and the lifetimes, intrinsic emission spectra, and radiative lifetimes of the transients were obtained by quantitative analysis. It was concluded that the initially populated S2 state is relaxed with a time constant of 45 fs to generate the S1 state retaining the perpendicular structure, and the D2d → D2 structural change (the change of the dihedral angle between the two ligand planes) occurs in the S1 state with a time constant of 660 fs. The intersystem crossing from the S1 state to the T1 state takes place after this structural dis...
199 citations
TL;DR: A theoretical investigation of the optical response and of the excited-state properties of three-arm and four-arm phenyl-cored dendrimers for photovoltaic applications and calculated reorganization energies were found to correlate well with the device photocurrent data where available.
Abstract: π-Conjugated dendrimers are an important class of materials for optoelectronic devices, especially for light-harvesting systems. We report here a theoretical investigation of the optical response and of the excited-state properties of three-arm and four-arm phenyl-cored dendrimers for photovoltaic applications. A variety of theoretical methods are used and evaluated against each other to calculate vertical transition energies, absorption and excitation spectra with vibronic structure, charge transport, and excitonic behavior upon photoexcitation and photoemission processes. Photophysical phenomena in these dendrimers are, in general, better explained with ab initio methods rather than with semiempirical techniques. Calculated reorganization energies were found to correlate well with the device photocurrent data where available. The excitons formed during photoexcitation are calculated to be more delocalized than the ones formed after vibrational relaxation in the excited states for fluorescence emission. ...
178 citations
TL;DR: A combined experimental and theoretical study is conducted on a series of model compounds in order to assess the combined role of branching and charge symmetry on absorption, photoluminescence, and two-photon absorption (TPA) properties.
Abstract: A combined experimental and theoretical study is conducted on a series of model compounds in order to assess the combined role of branching and charge symmetry on absorption, photoluminescence, and two-photon absorption (TPA) properties. The main issue of this study is to examine how branching of quadrupolar chomophores can lead to different consequences as compared to branching of dipolar chromophores. Hence, three structurally related pi-conjugated quadrupolar chromophores symmetrically substituted with donor end groups and one branched structure built from the assembly of three quadrupolar branches via a common donor moiety are used as model compounds. Their photophysical properties are studied using UV-vis spectroscopy, and the TPA spectra are determined through two-photon excited fluorescence experiments using femtosecond pulses in the 500-1000 nm range. Experimental studies are complemented by theoretical calculations. The applied theoretical methodology is based on time-dependent density functional theory, the Frenkel exciton model, and analysis in terms of the natural transition orbitals of relevant electronic states. Theory reveals that a symmetrical intramolecular charge transfer from the terminal donating groups to the middle of the molecule takes place in all quadrupolar chromophores upon photoexcitation. In contrast, branching via a central electron-donating triphenylamine moiety breaks the quadrupolar symmetry of the branches. Consequently, all Frank-Condon excited states have significant asymmetric multidimensional charge-transfer character upon excitation. Subsequent vibrational relaxation of the branched chromophore in the excited state leads to a localization of the excitation and fluorescence stemming from a single branch. As opposed to what was earlier observed when dipolar chromophores are branched via the same common electron-donating moiety, we find only a slight enhancement of the maximum TPA response of the branched compound with respect to an additive contribution of its quadrupolar branches. In contrast, substantial modifications of the spectral shape are observed. This is attributed to the subtle interplay of interbranch electronic coupling and asymmetry caused by branching.
120 citations
TL;DR: In this paper, femtosecond transient absorption spectroscopy was used to probe the excited state dynamics of multibranched chromophores and showed an increase of charge transfer character with an increase in branching, and this explains the relative increase in the two-photon cross section of the PRL series.
Abstract: Branched macromolecular structures are now an important area of research for enhanced two-photon absorption (TPA) cross sections. The mechanism of this enhancement has been suggested as a complex interplay between intramolecular interactions and the extent of charge-transfer character in the branches. In order to probe these processes more clearly, excited-state dynamics of multibranched chromophores by means of femtosecond transient absorption spectroscopy are reported. Investigations have been carried out on the PRL dye series (PRL-101, PRL-501, PRL-701), which have shown cooperative enhancement of the TPA cross section. Upon photoexcitation, transient absorption measurements have shown the presence of a localized charge-transfer (intramolecular charge transfer, ICT) state independent of branching. The results point to ultrafast localization of charge in this particular system of chromophores. Pump-probe measurements in highly polar solvents have shown the presence of a nonemissive charge-transfer state which is a solvent stabilized and conformationally relaxed state. The population of this nonemissive state increases from monomer to trimer, and thus, it has been used as indicator of the polar nature of the Franck-Condon state. These results have shown an increase of charge-transfer character of the excited state with an increase in branching, and this explains the relative increase in the two-photon cross section of the PRL series.
116 citations
TL;DR: In this paper, the beam asymmetry and differential cross-section for the reaction γp → ηp were measured from production threshold to 1500MeV photon laboratory energy.
Abstract: Beam asymmetry and differential cross-section for the reaction γp → ηp were measured from production threshold to 1500MeV photon laboratory energy. The two dominant neutral decay modes of the η -meson, η → 2γ and η → 3π0 , were analyzed. The full set of measurements is in good agreement with previously published results. Our data were compared with three models. They all fit satisfactorily the results but their respective resonance contributions are quite different. The possible photoexcitation of a narrow state N(1670) was investigated and no evidence was found.
109 citations
TL;DR: An agile optically controlled switch or modulator of terahertz (THz) radiation based on a one-dimensional photonic crystal with a GaAs wafer inserted in the middle as a defect layer is presented.
Abstract: We present an agile optically controlled switch or modulator of terahertz (THz) radiation. The element is based on a one-dimensional photonic crystal with a GaAs wafer inserted in the middle as a defect layer. The THz electric field is enhanced in the photonic structure at the surfaces of the GaAs wafer. Excitation of the front GaAs surface by ultrashort 810 nm laser pulses then leads to an efficient modulation of the THz beam even at low photocarrier concentrations (approximately 10(16) cm(-3)). The response time of the element to pulsed photoexcitation is about 130 ps.
104 citations
TL;DR: In this paper, a titanium fluorooxynitride (TiNxOyFz) was used as a visible-light-responsive photocatalyst for water oxidation into molecular oxygen.
Abstract: A titanium fluorooxynitride (TiNxOyFz) is studied as a visible-light-responsive photocatalyst. Nitridation of NH4TiOF3 at 773 K for 1 h under NH3 flow yields fine particulate TiNxOyFz (particle size, 100−300 nm) with an anatase crystal structure and high crystallinity. X-ray diffraction and absorption measurements confirm that the TiNxOyFz material exhibits similar structural characteristics to anatase TiO2. The energy gap of TiNxOyFz is estimated to be 2.34 eV, substantially smaller than the band gap energy of TiO2 with the same anatase crystal structure (3.26 eV). Density functional theory calculations indicate that the bottom of the conduction band of TiNxOyFz is composed of empty Ti3d orbitals and that the doping level is formed by N2p orbitals in the forbidden band above the valence band consisting of O2p orbitals. TiNxOyFz is demonstrated to function as a visible-light-driven photocatalyst for water oxidation into molecular oxygen at wavelengths as long as 540 nm through photoexcitation from the N2p...
99 citations
TL;DR: The simulation results provide a basis for understanding several spectroscopic observations at molecular levels, including ultrafast dynamic Stokes shift, multicomponent fluorescence, viscosity dependence of the fluorescence lifetime, and radiationless decay from electronically excited state to the ground state along the isomerization coordinate.
Abstract: Detailed simulation study is reported for the excited-state dynamics of photoisomerization of cis-tetraphenylethylene (TPE) following excitation by a femtosecond laser pulse. The technique for this investigation is semiclassical dynamics simulation, which is described briefly in the paper. Upon photoexcitation by a femtosecond laser pulse, the stretching motion of the ethylenic bond of TPE is initially excited, leading to a significant lengthening of ethylenic bond in 300 fs. Twisting motion about the ethylenic bond is activated by the energy released from the relaxation of the stretching mode. The 90 degrees twisting about the ethylenic bond from an approximately planar geometry to nearly a perpendicular conformation in the electronically excited state is completed in 600 fs. The torsional dynamics of phenyl rings which is temporally lagging behind occurs at about 5 ps. Finally, the twisted TPE reverts to the initial conformation along the twisting coordinate through nonadiabatic transitions. The simulation results provide a basis for understanding several spectroscopic observations at molecular levels, including ultrafast dynamic Stokes shift, multicomponent fluorescence, viscosity dependence of the fluorescence lifetime, and radiationless decay from electronically excited state to the ground state along the isomerization coordinate. (C) 2007 American Institute of Physics.
TL;DR: In this article, the beam asymmetry and differential cross section for the reaction gamma+p->eta+p were measured from production threshold to 1500 MeV photon laboratory energy, and the two dominant neutral decay modes of the eta meson, eta->2g and eta-3pi0, were analyzed.
Abstract: Beam asymmetry and differential cross section for the reaction gamma+p->eta+p were measured from production threshold to 1500 MeV photon laboratory energy. The two dominant neutral decay modes of the eta meson, eta->2g and eta->3pi0, were analyzed. The full set of measurements is in good agreement with previously published results. Our data were compared with three models. They all fit satisfactorily the results but their respective resonance contributions are quite different. The possible photoexcitation of a narrow state N(1670) was investigated and no evidence was found.
TL;DR: LuLuque and Marti as mentioned in this paper analyzed the fundamental limits to power generation in quantum solar cells, and showed that an upper efficiency of 44.5% is achievable due to single photon absorption only.
Abstract: The intermediate band solar cell has been proposed as an ultrahigh efficiency source of energy due to the possibility of absorption of two sequential sub-band-gap photons to excite charge from a quantum confined (e.g., quantum dot or well) region into the large band gap barrier region [A. Luque and A. Marti, Phys. Rev. Lett. 78, 5014 (1997)]. Unfortunately, high efficiencies using this structure have not yet been realized. Here, we analyze the fundamental limits to power generation in quantum solar cells. When a difference in quasi-Fermi energies between the barrier and the quantum well regions exists due to the presence of photogenerated charge, an upper efficiency limit of 44.5% is achievable due to single photon absorption only. This efficiency is significantly higher than the Shockley-Queisser limit of ∼31% for homojunction cells, but remains below that predicted for two photon excitation (>63%) previously predicted for quantum cells.
TL;DR: In this paper, the authors studied the resonance energy transfer in nanoassemblies of CdSe/ZnS quantum dots and pyridyl-substituted free-base porphyrin molecules.
Abstract: The observed resonance energy transfer in nanoassemblies of CdSe/ZnS quantum dots and pyridyl-substituted free-base porphyrin molecules [Zenkevich et al., J. Phys. Chem. B 109 (2005) 8679] is studied computationally by ab initio electronic structure and quantum dynamics approaches. The system harvests light in a broad energy range and can transfer the excitation from the dot through the porphyrin to oxygen, generating singlet oxygen for medical applications. The geometric structure, electronic energies, and transition dipole moments are derived by density functional theory and are utilized for calculating the F¨ orster coupling between the excitons residing on the quantum dot and the porphyrin. The direction and rate of the irreversible exciton transfer is determined by the initial photoexcitation of the dot, the dot–porphyrin coupling and the interaction to the electronic subsystem with the vibrational environment. The simulated electronic structure and dynamics are in good agreement with the experimental data and provide real-time atomistic details of the energy transfer mechanism. © 2007 Elsevier B.V. All rights reserved.
TL;DR: Guo et al. as mentioned in this paper developed an open-aperture Gaussian-beam Z-scan theory for evaluating the property of the saturable absorption originating from two-photon absorption (2PA) transition, when a spatial Gaussian beam is used as the excitation source.
Abstract: In our article [B. Gu, Y. X. Fan, J. Wang, J. Chen, J. P. Ding, H. T. Wang, and B. Guo, Phys. Rev. A 73, 065803 (2006)] we have presented the theory of open-aperture Gaussian-beam Z-scan, based on the Adomian decomposition method, which is available only for the saturable absorption caused by single-photon absorption transition. In the present article, using the same technique (Adomian decomposition method, as a common technique), we develop an open-aperture Z-scan theory for evaluating the property of the saturable absorption originating from two-photon absorption (2PA) transition, when a spatial Gaussian beam is used as the excitation source. We find analytic polynomial expressions of the Z-scan traces for a continuous wave laser or a temporal Gaussian pulsed laser. As the experimental evidence, we investigate the saturable 2PA behaviors caused by the interband two-photon transition in the direct-gap II–VI semiconductors CdS, CdSe, ZnSe, and ZnTe, under the excitation condition of a femtosecond laser wi...
TL;DR: In this paper, the photoexcitation of surface plasmons at an Ag-SiO2 interface is numerically demonstrated to yield a 50% coupling efficiency from a Gaussian beam into surface plasmon voltages and currents.
Abstract: The efficient generation of surface plasmons from free-space optical waves is still an open problem in the field. Here we present a methodology and optimized design for a grating coupler. The photoexcitation of surface plasmons at an Ag-SiO2 interface is numerically demonstrated to yield a 50% coupling efficiency from a Gaussian beam into surface plasmon voltages and currents.
TL;DR: In this paper, the bias above the trap-filling limit in the as-is polymer generates a new set of exponential traps, which can be detrapped by photoexcitation.
Abstract: Ethyl-hexyl substituted polyfluorene (PF) with its high level of molecular disorder can be described very well by one-carrier space-charge-limited conduction for a discrete set of trap levels with energy � 0.5 eV above the valence band edge. Sweeping the bias above the trap-filling limit in the as-is polymer generates a new set of exponential traps, which is clearly seen in the density of states calculations. The trapped charges in the new set of traps have very long lifetimes and can be detrapped by photoexcitation. Thermal cycling the PF film to a crystalline phase prevents creation of additional traps at higher voltages.
TL;DR: The experimentally observed anomalous solvent effect on the two-photon absorption of dialkylamino substituted distyrylbenzene chromophores cannot be attributed to the intrinsic properties of a single molecule and its interaction with solvents.
Abstract: Solvent effects on the two-photon absorption of a symmetrical diamino substituted distyrylbenzene chromophore have been studied using the density functional response theory in combination with the polarizable continuum model. It is shown that the dielectric medium has a rather small effect both on the bond length alternation and on the one-photon absorption spectrum, but it affects significantly the two-photon absorption cross section. It is found that both one- and two-photon absorptions are extremely sensitive to the planarity of the molecule, and the absorption intensity can be dramatically reduced by the conformation distortion. It has led to the conclusion that the experimentally observed anomalous solvent effect on the two-photon absorption of dialkylamino substituted distyrylbenzene chromophores cannot be attributed to the intrinsic properties of a single molecule and its interaction with solvents.
Journal Article•
TL;DR: In this paper, the authors investigate theoretically the efficiency of intramolecular hot-carrier-induced impact ionization and excitation processes in carbon nanotubes and show that strong excitonic coupling favors neutral excitations over ionization, while the impact mechanism populates a different set of states than that produced by photoexcitation.
Abstract: We investigate theoretically the efficiency of intramolecular hot-carrier-induced impact ionization and excitation processes in carbon nanotubes. The electron confinement and reduced screening lead to drastically enhanced excitation efficiencies over those in bulk materials. Strong excitonic coupling favors neutral excitations over ionization, while the impact mechanism populates a different set of states than that produced by photoexcitation. The excitation rate is strongly affected by optical phonon excitation and a simple scaling of the rate with the field strength and optical phonon temperature is obtained.
TL;DR: In this article, coherent phase control of resonance mediated three-photon absorption in Na was studied both theoretically and experimentally, and the regime is perturbative of third order.
Abstract: Femtosecond coherent phase control of resonance mediated $(2+1)$ three-photon absorption is studied both theoretically and experimentally. The regime is perturbative of third order. The photoexcitation coherently combines elements of both nonresonant and resonance-mediated multiphoton transitions. By proper simple pulse shaping the three-photon absorption in Na is effectively controlled experimentally, enhanced up to $\ensuremath{\sim}300%$ of the absorption induced by the transform-limited pulse. It is achieved by phase manipulating intra- and intergroup interferences involving two groups of three-photon excitation pathways: (i) on resonance and (ii) near resonance with the intermediate resonance state accessed by nonresonant two-photon transition.
TL;DR: In this article, a near-field heterodyne transient grating method was proposed for photoexcitation in the nanosecond to millisecond range, where pump and probe beams are impinged on a transmission grating placed in front of a sample.
TL;DR: The photochemically relevant C=C stretching and C-H deformation vibrational modes were found to exhibit maximum resonance Raman intensity and structural change upon photoexcitation for thymine, suggesting that the initial dynamics of thymine lie along the photochemical reaction coordinate.
Abstract: To explore the excited-state structural dynamics of thymine, a DNA nucleobase, we measured the resonance Raman spectra of thymine in aqueous solution at wavelengths throughout the lowest-energy absorption band. Self-consistent analysis of the resulting resonance Raman excitation profiles and absorption spectrum using a time-dependent wave packet formalism yielded the excited-state structural dynamics. The photochemically relevant C=C stretching and C-H deformation vibrational modes were found to exhibit maximum resonance Raman intensity and structural change upon photoexcitation for thymine, suggesting that the initial dynamics of thymine lie along the photochemical reaction coordinate.
TL;DR: The hypothesis that the initial photoexcitation step of the [Ru2Pd2] complex is a charge-transfer excitation from the ruthenium atoms to the adjacent butyl-2,2'-bipyridine ligands is supported.
Abstract: Ruthenium−polypyridine and related complexes play an important role as models for light-harvesting antenna systems to be employed in artificial photosynthesis. In this theoretical and experimental work, the first photoexcitation step of a tetranuclear [Ru2Pd2] complex composed of two ruthenium−bipyridyl subunits and two palladium-based fragments, {[(tbbpy)2Ru(tmbi)]2[Pd(allyl)]2}2+ (tbbpy = 4,4‘-di-tert-butyl-2,2‘-bipyridine, tmbi = 5,6,5‘,6‘-tetramethyl-2,2‘-bibenzimidazolate), is investigated by means of experimental and theoretical resonance Raman spectroscopy. The calculated spectra, which were obtained within the short-time approximation combined with time-dependent density functional theory (TDDFT), reproduce the experimental spectrum with excellent agreement. We also compared calculations on off-resonance Raman spectra, for which a completely different theoretical approach has to be used, to experimental ones and again found very good agreement. The [Ru2Pd2] complex represents the probably largest ...
TL;DR: In this paper, transient photoinduced absorption measurements along with optical absorption and photoluminescence (PL) emission reveal that the light-absorption process takes place in defects related to strong PL emission, suggesting that the photoexcited carriers are in oxygen-related interface states.
Abstract: The authors have studied transient photoinduced absorption in single monolayers of oxidized silicon nanocrystals. Transient photoinduced absorption measurements along with optical absorption and photoluminescence (PL) emission reveal that the light-absorption process takes place in defects related to strong PL emission, suggesting that the photoexcited carriers are in oxygen-related interface states. They have time-resolved ultrafast relaxation paths in oxygen-related states and quantized sublevels, which have important implications in the understanding of fundamental optical properties for this system.
TL;DR: This work characterized several spectroscopic properties of commercial, streptavidin functionalized quantum dots (QD525, lot 1005-0045, and QD585, lot 0905-0031), the first step in the development of calibration beads to be used in a generalizable quantification scheme of multiple fluorescent tags in flow cytometry or microscopy applications.
TL;DR: Comparison between experimental and theoretical RFPADs indicates that the recoil angle for NO+ fragments is approximately 50 degrees relative to the symmetry axis of the initial C2v symmetry of the NO2 molecule in the ionization leading to the (1a2)-1 b 3A2 state and the recoil angles are approximately 120 degrees for the O+ fragment for ionization Leading to the(4a1)-1 3A1 state.
Abstract: The authors report measured and computed molecular frame photoelectron angular distributions (MFPADs) and recoil frame photoelectron angular distributions (RFPADs) for the single photon ionization of the nonlinear molecule NO2 leading to the (1a2)−1bA23 and (4a1)−1A13 states of NO2+. Experimentally, the RFPADs were obtained using the vector correlation approach applied to the dissociative photoionization (DPI) involving these molecular ionic states. The polar and azimuthal angle dependences of the photoelectron angular distributions are measured relative to the reference frame provided by the ion recoil axis and direction of polarization of the linearly polarized light. Experimental results are reported for the photon excitation energies hν=14.4 and 22.0eV. Theoretically the authors give expressions for both the MFPAD and the RFPAD. They show that the functional form in the recoil frame, where an average over the azimuthal dependence of the molecular fragments about the recoil direction is made, is identi...
TL;DR: In this article, photoexcitation dependent Raman studies on the optical phonon mode in silicon nanostructures (Si NS) prepared by laser-induced etching are done, and the increase in the asymmetry of the Raman spectra on the increasing laser power density is attributed to Fano interference between discrete optical phonons and continuum of electronic excitations in the few nanometer size nanoparticles made by laser induced etching.
Abstract: Photoexcitation dependent Raman studies on the optical phonon mode in silicon nanostructures (Si NS) prepared by laser-induced etching are done here. The increase in the asymmetry of the Raman spectra on the increasing laser power density is attributed to Fano interference between discrete optical phonons and continuum of electronic excitations in the few nanometer size nanoparticles made by laser-induced etching. No such changes are observed for the same laser power density in the crystalline silicon sample or ion-implanted silicon sample followed by laser annealing. A broad photoluminescence spectrum from Si NS contains multiple peak behavior, which reveals the presence of continuum of electronic states in the Si NS.
TL;DR: The reaction mechanism underlying the photoinduced linkage isomerization of discrete arsenic-sulfur clusters in the realgar form of tetraarsenic tetrasulfide to its pararealgar form was studied on a natural specimen of the mineral with a combination of in situ single-crystal X-ray photodiffraction and Fourier transform infrared spectroscopy.
Abstract: The reaction mechanism underlying the photoinduced linkage isomerization of discrete arsenic−sulfur clusters in the realgar form of tetraarsenic tetrasulfide (α-As4S4) to its pararealgar form was studied on a natural specimen of the mineral with a combination of in situ single-crystal X-ray photodiffraction and Fourier transform infrared spectroscopy. The photodiffraction technique provided direct atomic resolution evidence of formation of intermediate As4S5 phase in which half of the realgar molecule is retained in its envelope-type conformation, while the other half is transformed by effective switching of positions of one sulfur and one arsenic atom. The initiation and propagation stages of the process are studied under light and dark conditions, during and after photoexcitation with polychromatic visible light. In the “light” reaction stage, the interatomic and cell parameters averaged over the crystal volume and photoexcitation time remain almost unchanged. The residual electron density features are ...
TL;DR: In this article, the authors investigated the photoresponse of β-In2S3 thin films with a band gap of ∼2.67eV and found that the photoconductive response to extrinsic photoexcitation could be removed when the film stoichiometry was changed.
Abstract: β-In2S3 thin films with a band gap of ∼2.67eV exhibited persistent photoconductivity when excited using photons with energy of 1.96 eV. The photoconductive response to extrinsic photoexcitation could be removed when the film stoichiometry was changed. Photoluminescence studies in the films revealed an emission of 1.826 eV, due to donor–acceptor pair (DAP) recombination, which was absent in the film not responding to extrinsic excitation. Hence, it was concluded that presence of the DAP was responsible for the extrinsic photoconductivity under the 1.96 eV excitation. This study can initiate further a methodology for tailoring the photoresponse of this semiconducting thin film by spatially controlling the film stoichiometry.
TL;DR: In this paper, a study of the luminescence of lithium borate crystals (Li6Gd(BO3)3 doped by Eu3+ and Ce3+ ions, Li5.7Mg0.15Gd (BO3), Eu, and Li6Eu(BO 3)3) initiated by selective excitation by synchrotron radiation at excitation energies of 3.7-27 eV at 10 and 290 K.
Abstract: The paper reports on a study of the luminescence of lithium borate crystals (Li6Gd(BO3)3 doped by Eu3+ and Ce3+ ions, Li5.7Mg0.15Gd(BO3)3: Eu, and Li6Eu(BO3)3) initiated by selective excitation by synchrotron radiation at excitation energies of 3.7–27 eV at 10 and 290 K. Efficient energy transfer between the rare-earth ions Gd3+ → Ce3+ and Gd3+ → Eu3+ was found to proceed by the resonance mechanism, as well as by electron-hole recombination. Fast decay kinetics of luminescence of the Ce3+ activator centers was studied under intracenter photoexcitation and excitation in the interband transition region. The mechanisms involved in luminescence excitation and radiative relaxation of electronic states of rare-earth ions are analyzed, and the energy transfer processes operating in these crystals are discussed.