The yttrium monohydride spectrum in the range 12 500-25 000 cm−1 has been studied by various laser-induced fluorescence (LIF) techniques. YH (YD) molecules have been produced in a free jet molecular beam apparatus by a laser vaporizing yttrium metal in the presence of He doped with H2 (D2) or NH3 (ND3). Low-resolution (∼0.04 cm−1) excitation spectra have been recorded in the entire studied range. Four green bands (19 300-19 900 cm−1) of the YH isotopomer have been studied in more detail: (1) high-resolution (∼120 MHz, ∼0.004 cm−1) excitation spectra have been recorded, (2) dispersed fluorescence spectra have been obtained, and (3) lifetimes of the selected rotational levels of the upper states have been measured. Our observations have confirmed that the ground state of yttrium monohydride has 1Σ+ symmetry and have provided a link between the singlet and triplet manifolds. The upper states of the observed transitions have been tentatively assigned to five electronic states, d0+, f3Π, f′1, D1Π, E0+, and Fl. The low-energy excited electronic state observed in the dispersed fluorescence experiment has been assigned as the a3Δ state. 相似文献
Photoinduced charge-trapping is a promising strategy for boosting the photosensitivity of organic photodetectors at the expense of their response time. In addition, they have a low carrier extraction yield due to the formation of low-energy triplet excitons through the recombination of a photogenerated hole–electron pair. Materials with thermally activated delayed fluorescence (TADF) exhibit a long-lived (≈µs) excited spin-triplet nearly iso-energetically aligned with that of an excited spin-singlet, which results in suppressed exciton losses and is widely used in organic light-emitting diodes. The extraction and population of triplet state excitons in TADFs is a sought-after but underexplored aspect of photoinduced gating in photodetectors. A 1,2,3,5-tetrakis(carbazol-9-yl)4,6-Dicyanobenzene (4CzIPN) TADF blend with a high-mobility Poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT-C14) polymer via bulk type-II offset can increase free carrier extraction yield (fast response) and retain trapped electrons in TADF triplet states (high gain). The PBTTT-C14/4CzIPN ultraviolet photodetector device maintains a trade-off between high photogain (≈103) and fast response time (79 ms) at 300 nm while operating at a shallow dark current (≈pA). Furthermore, the device shows high external quantum efficiency (≈104 %) and detectivity (≈1011 Jones) for low light power (<pW). The innovative application of TADF material can lead to exciting new developments in organic-based high-performance photodetection. 相似文献
A triplet diphenylcarbene, bis[3-bromo-5-(trifluoromethyl)[1,1'-biphenyl]-4-yl]methylidene (B3B), with exceptional stability was discovered by chemists from Japan's Mie University. To investigate its different quantum chemical features, a theoretical analysis was predicated on Density Functional Theory (DFT) and Time Dependent-DFT (TD-DFT) based technique. According to the findings, the singlet–triplet energy gap (ES-T), as well as HOMO–LUMO energy bandgap (EH-L), was found to be diminished when nucleophilicity (N) rose. We looked at the geometrical dimensions, molecular orbitals (MOs), electronic spectra, electrostatic potential, molecular surfaces, reactivity characteristics, and thermodynamics features of the title carbene (B3B). Its electronic spectra in different solvents were calculated using TD-DFT and Polarizable Continuum Model (PCM) framework. The estimated absorption maxima of B3B were seen between 327 and 340 nm, relying on the solvents, and were attributed to the S0?→?S1 transition. Estimated fluorescence spectral peaks were found around 389 and 407 nm with the S1 and S0 transitions being identified. Its fluorescence/absorption intensities revealed a blue shift change when the solvent polarity was increased. The least exciting state has been discovered to be the π?→?π* charge-transfer (CT) phase. According to the Natural Bonding Orbital (NBO) exploration, ICT offers a significant role in chemical system destabilization. Furthermore, several hybrid features were used to determine the NLO (nonlinear optical) features (polarizability, first-order hyperpolarizability, and dipole moment). The calculated values suggest that B3B is a promising candidate for further research into nonlinear optical properties.
The manifestation of ion pairs in the absorption and emission of fluorescence by symmetric indotricarbocyanine dyes with the same cation and anions Br, I, and BF4 in ethanol, methylene chloride, and dichlorobenzene has been investigated. It is shown that the formation of ion pairs on passing to low-polarity solvents, along with the changes in the electronic absorption and emission spectra, manifests itself in the polarization and fluorescence excitation spectra. We were the first to establish that the presence of an equilibrium mixture of contact ion pairs and free ions in solutions has an effect on the position and probabilities of transitions not only for the first but also for higher excited singlet states of the molecules of polymethine dyes. The formation of ion pairs manifests itself more clearly when the spectral-luminescence properties of compounds in the shortwave spectral region are analyzed. It has been established that marked changes arise in the absorption, excitation, emission, and polarization fluorescence spectra, as well as in the lifetime and quantum yield of fluorescence in this spectral region when the solvent is changed. 相似文献
By the delayed fluorescence activated by direct multiphoton excitation of triplet molecules by CO2–laser radiation we have studied the prevailing deactivation pathways of triplet molecules with a high store of vibrational energy Evib. The dependences of the kinetic characteristics of delayed fluorescence on the presence of vapors and foreign gases have been used to estimate the rates and efficiencies of intermolecular vibrational relaxation in the vibrational quasi–continuum of the triplet state T1. By the changes in the intensities and decay rates over a wide range of vibrational energies we have established the Evib dependences of reversible intercombination conversion between the states T1 and S1 and interconversion from T1 to the ground electronic state S0 for both the case of isolated excited molecules and at a steady vibrational temperature. It is shown that at high vibrational temperatures the radiationless transition from the T1 state to S0 has an activation character and is accomplished through the energy barrier. The conditions for going to an exponential dependence have been determined. It has been found that the obtained dependences are in good agreement with the known experimental results. The influence of molecular and environmental characteristics on the decay rate of triplet molecules is compared. 相似文献
It has been shown that the excitation of autoionization states at collisions of keV ions with a solid is decisive for inelastic energy loss and, correspondingly, the electronic stopping power dE/dx. It has been proposed to estimate the electronic stopping power dE/dx using the relation of cross sections for the excitation of autoionization states to ionization cross sections. When ionization cross sections are unknown, scaling is used to calculate ionization cross sections at the excitation of the L and M shells. A threshold dependence of the electronic stopping power dE/dx on the energy of bombarding ions has been predicted. 相似文献
High efficiency,stable organic light-emitting diodes(OLEDs)based on 2-pheyl-4'-carbazole-9-H-Thioxanthen-9-one-10,10-dioxide(TXO-PhCz)with different doping concentration are constructed.The stability of the encapsulated devices are investigated in detail.The devices with the 10wt% doped TXO-PhCz emitter layer(EML)show the best performance with a current efficiency of 52.1 cd/A,a power efficiency of 32.7lm/W,and an external quantum efficiency(EQE)of 17.7%.The devices based on the 10wt%-doped TXO-PhCz EML show the best operational stability with a half-life time(LT50)of 80 h,which is 8h longer than that of the reference devices based on fac-tris(2-phenylpyridinato)iridium(Ⅲ)(fr(ppy)_3).These indicate excellent stability of TXO-PhCz for redox and oxidation processes under electrical excitation and TXO-PhCz can be potentially used as the emitters for OLEDs with high efficiency and excellent stability.The high-performance device based on TXO-PhCz with high stability can be further improved by the optimization of the encapsulation technology and the development of a new host for TXO-PhCz. 相似文献
By the spectral and kinetic characteristics of the luminescence of vapors of polyatomic molecules (anthracene, anthraquinone, fluorenone) initiated by selective IR multiphoton excitation (IR MPE) of molecules in the ground electronic state S0 the relaxation processes proceeding under vibrational excitation of molecules to energies exceeding the energies of the lower excited electronic states have been investigated. The changes in the spectral and kinetic characteristics with increasing CO2 laser energy density and vapor Pv and foreign gas pressure PFG are analyzed. They are similar to the characteristics obtained for normal fluorescence of these molecules with changing vibrational energy Evib content. On the basis of experimental data and model calculations it has been concluded that at the laser radiation densities used in the case of IR MPE the molecules reach energies considerably exceeding the energies of the electronic levels. It is shown that a nonadiabatic connection between the electronic states leads to the population of mixed electronic states isoenergetic to the vibrational levels of the ground electronic state and to emission of delayed luminescence spectrally identical to the normal luminescence of these molecules. It has been found that when high vibrational levels are populated, new relaxation channels, such as reverse electron relaxation, emission from high vibrational levels of the ground electronic state, and multiquantum vibrational energy transfer at collisions leading to a rapid establishment of vibrational equilibrium become important. 相似文献
Journal of Applied Spectroscopy - Spectral and luminescent characteristics and the duration of fluorescence were measured for a series of metal-free tetrapyrroles in polyvinylbutyral solid films at... 相似文献
We present an analysis of the A0(+)(6(3)P(1))-->X0(+)(6(1)S(0)) bound-bound and bound-free fluorescence spectrum, and of the A0(+)(6(3)P(1))<--X0(+)(6(1)S(0)) and B1(6(3)P(1))<--X0(+)(6(1)S(0)) bound-bound excitation spectrum of the HgKr van der Waals molecule. The A-->X fluorescence spectrum, which was observed for the first time, as well as the excitation spectra were recorded using a pulsed supersonic molecular beam crossed with a pulsed dye laser beam. An analysis of the A(v')<--X(v"), B(v')<--X(v"), and A(v'=8)-->X(v") bound-bound bands indicates that a Morse function combined with a long-range approximation represents the interatomic potential energy curve of the A, B, and X states below the dissociation limit. In the simulation of the A(v'=8)-->X bound-free spectrum the Morse, Lennard-Jones (n-6), and Maitland-Smith (n(0), n(1)) functions were tested, and the Maitland-Smith (11.39, 10.50) potential was found to be a good representation of the repulsive part of the X-state PE curve above the dissociation limit, over the internuclear separation range R=2.85-3.55 ?. The spectroscopic characteristics for the A, B, and X states obtained in this work are compared with other available experimental and theoretical results. Copyright 2001 Academic Press. 相似文献