Resonant Secondary Radiation Research Articles

Resonance Secondary Radiation enhanced by quadrupole mode of plasmonic arrays

In this paper, the Resonance Secondary Radiation (RSR), the joined action of the Raman Resonance and Fluorescence emission is described. The observed enhancement of the RSR signal is caused by the quadrupole mode of the plasmonic resonance of gold nanotriangles arrays. The material used in this study has been designed based on two separate nanoscale engineering processes by combining two different materials (oligonucleotides and colloidal arrays) at different length scales. The control of the emission by the plasmonic resonance is demonstrated and thoroughly investigated using extinction, steady state and time-resolved Fluorescence spectroscopy.

Vibronic relaxation processes of the FA center in RbCl:Li

The vibronic relaxation process of FA centers in RbCl:Li, which have Type I emission at low temperatures and Type II emission at high temperatures, has been studied at 10 and 77K by measuring the resonant secondary radiation (RSR) spectrum from optically excited FA centers with pico-second time-resolved spectroscopy. This study has been prompted by the quest to improve our knowledge on the de-excitation process in the FA centers. The adiabatic potential energy curves are deduced from a theoretical analysis of the measured RSR spectra and compared with those already known. It is shown that Type II relaxation observed at 77K occurs after Type I relaxation, supporting in turn a model proposed by Baldacchini et al. based on photoluminescence measurements.

Wavepacket Motion in Self-Trapped Exciton of Quasi-One-Dimensional Halogen-Bridged Pt Complex, [Pt(en)2][Pt(en)2I2] (ClO4)4, Observed by Femtosecond Time Resolved Luminescence Spectroscopy

We report on the time-resolved luminescence spectroscopy of a quasi-one-dimensional halogen-bridged platinum complex, [Pt(en) 2 ][Pt(en) 2 I 2 ] (ClO 4 ) 4 , at room temperature in the energy range between 1.2 and 0.9 eV. A strong first peak at the time origin and subsequent oscillating features were observed in the time evolution curves of luminescence intensity. As the frequency of the wavepacket oscillation in the self-trapped exciton, we obtained 2.92 THz (97 cm -1 ), which is 77% of the symmetric stretching mode frequency in the ground state. We analyzed the measured time evolution of the luminescence intensity by using the theory of resonant secondary radiation.

Nuclear wave-packet dynamics on nearly degenerate two adiabatic potential energy surfaces in the excited state of KIFcenters

Nuclear wave-packet dynamics in the excited state of KI $F$ centers is investigated by using time-resolved luminescence spectroscopy based on the up-conversion technique. The observed transient spectrum involves an oscillatory and a nonoscillatory component. The origins of these components are interrogated by comparing the results with a model calculation based on the resonant secondary radiation theory. The oscillatory part reflects the coupling of the $2s$-like electron mainly to the totally symmetric local mode around the $F$ center. The nonoscillatory part reflects the incoherent population of the vibrational levels in the $2p$-like state, which couples to many bulk phonon modes with a broad density of state. The model calculation suggests that the transition probability to the $2p$-like state is approximately 0.05.

Wavepacket Dynamics at Low Temperature in Localized Excitons of the Quasi-One-Dimensional Br-Bridged Pt Complex Studied by Femtosecond Luminescence Spectroscopy

We report on the femtosecond time-resolved luminescence spectroscopy in a quasi-one-dimensional halogen-bridged mixed valence platinum complex, [Pt(en) 2 ][Pt(en) 2 Br 2 ](ClO 4 ) 4 at low temperatures. From the temperature dependence of the lifetime of the self-trapped excitons (STEs), we estimated the potential barrier height in the direction to the non-radiative path to be 99±10 meV. The observed time-evolutions of the luminescence excited by 1.57 eV photons at 4 K show complicated behavior, which is considerably different from that at room temperature. From Fourier transform of the time domain data, a low frequency mode was found at 0.7 THz in addition to the main mode at 3.4 THz, which has been assigned to the motion of the halogen ions in the self-trapped excitons. Incorporating two modes into the model based on the theory of resonant secondary radiation, the experimental data are well reproduced. This result shows that the wavepacket moves on the two-dimensional adiabatic potential surface of the s...

Broad Raman scattering and luminescence in β-carotene solution

Resonant secondary radiation spectra of dilute β-carotene solution (10−4–10−5 M) are measured under stationary excitation. The excitation energy is varied within 0–0 and 0–1 transition energies in the S2–S0 transition of β-carotene. When the excitation energy is varied from the peak of the 0–0 absorption band to the low-energy side at 60 K and 175 K, (a) the line shape of 0–0 emission band changes from symmetric to asymmetric, and (b) the intensity of luminescence rapidly decreases as compared with the intensity of Raman scattering by ν1, ν2, and ν3 intramolecular vibronic modes of β-carotene. When the 0–1 absorption band is excited, we successfully separate luminescence and broad Raman component (BR), which is resonant Raman scattering of low-frequency phonon modes in solution. The line shape of the density of vibronic states weighed by the coupling strength between electronic states in a dye molecule and vibrations of the surrounding atoms (WDOS) is determined by BR. Taking into account inhomogeneous broadening and assuming linear electron–phonon coupling, the resonant secondary radiation spectra are calculated using obtained WDOS. The above characters of the experimental results (a) and (b) are well reproduced by the calculations.

Observation of ‘broad Raman’ component in resonant secondary radiation

The broad Raman component in resonant secondary radiation in β-carotene solution is observed for the first time. The characters obtained are as follows: the line shape is independent of excitation energy; the Stokes to anti-Stokes intensity ratio is n(ω)+1: n(ω) with a Bose factor n( ω); the width at Stokes side is about 150 cm −1 ; the integrated intensity decreases toward off-resonant excitation. The broad Raman component has the detailed information on electron–phonon interaction and optical dephasing.

Hot luminescence from F centers in KCl studied by time-resolved polarization spectroscopy

A dynamical de-excitation process for optically excited electrons in F centers in KCl is studied by using time-resolved polarization spectroscopy. The ordinary luminescence (OL) and the hot luminescence (HL) in the OL region are separated from a resonant secondary radiation, and the HL is decomposed into two components with different behaviors. They are the HL in a short time after excitation and an emission from 2p-like states after a long time from excitation. The dynamics of the optical excitation is interpreted phenomenologically in terms of a configuration coordinate model.

Picosecond Transient Raman Spectra of S1 Bis(Methylstyryl)- Benzene: Observation of S1←SnResonance Emission

We have been studying the excited state spectra of several molecules related to electroluminescent conducting polymers. The excited state structure corresponds to the conducting state in these systems. We have obtained data on 1,4-bis(2,2′-methylstyryl)- benzene (2MSB) as a model system of poly (P-phenylenevinylene) (PPV). We observe both sharp and broad features in the spectra. The sharp bands occur at a constant energy shift relative to the probe wavelength. We attribute the sharp bands to resonance Raman bands of the S1 state of 2MSB. We assign the broad band at ∼740 nm to resonance emission between Sn and S1. We believe that this is the first observation of resonance secondary radiation (RSR) between two electronically excited states in a large molecule.

Early Days and Later Development of Resonance Raman Spectroscopy

The development of the simplest variant of the semi-classical theory of the Raman effect (RE) resulted in the establishment of two main mechanisms of this phenomenon, favoured the formation of a new direction—Raman line excitation spectroscopy, and stimulated the search for conditions of excitation of Raman scattering (RS) by molecules near and in absorption bands. The change in the traditional experimental conditions made it possible to obtain distinct Raman lines ofp-nitroaniline in the region of a very intense band of the electronic vibrational absorption spectrum, i.e. under the conditions of resonance between the incident light wave and electronic oscillator. Owing to the improvements in experimental techniques, it became possible to obtain resonance Raman spectra of almost any classes of chemical compounds and to observe any forms of resonance RE. Further development of the quantum and classical theories made it possible to describe the main types of resonance secondary radiation in spectral and time scanning, to establish the interrelations between electronic vibrational absorption spectra, light scattering (RS), fluorescence and phenomena of intermediate types, to estimate more correctly the possibilities of distinguishing such notions as one- or two-photon processes, virtual and real transitions, light scattering and fluorescence and to compare more correctly the notions of the transformation of one photon and the statistical ensemble of photons. Problems relating to further investigations according to the possibilities of modern experimental and theoretical physics are discussed. © 1997 John Wiley & Sons, Ltd.

Time-resolved picosecond spectroscopy of the resonant secondary radiation of F centers in KCl

Abstract The linear polarization (P HL) of hot luminescence (HL) composing of the resonant secondary radiation of the F centers has been measured using a time-resolved picosecond spectroscopy over the whole Stokes wavenumber Ω range. The P HL holds constant value of about 40% until the onset of ordinary luminescence (OL), from where it decreases to vanishingly small with decrease of Ω This implies that the optically excited F center relaxes down along the 2p-like adiabatic potential energy surface (APES) trough, and transits to the 2s-like APES trough to form the relaxed excited state (RES). The lattice relaxation time and the dynamical transition time are ultra fast estimated to be less than 15 psec.

Picosecond spectroscopy of the resonant secondary radiation of F centers in KCl

Resonant secondary radiation of F centers in KCl is studied, using time-resolved picosecond spectroscopy. A novel mechanism is proposed, viz., that the optically excited F electron is de-excited as the lattice relaxes in a 2p adiabatic potential.

Theory of resonant secondary radiation via an exciton strongly coupled with phonons

Abstract Recent progress in the theory of resonant secondary radiation from a strongly-coupled excitonphonon system is briefly reviewed. Implication of some calculated results on the self-trapping process of hot excitons is discussed.

An experimental study of radiation-induced pure dephasing: ArF excited emission of O2

The effects of incoherent incident light on both nonresonant and resonant secondary radiation (RSR) are demonstrated for the spontaneous emission of O2. ArF excimer radiation (FWHH∼120 cm−1) is resonant with several rovibronic features of the v′=4 band of the Schumann–Runge absorption system. Off-resonant contributions to the RSR spectrum are Raman-like (v″=1) but carry the linewidth of the incident incoherent radiation. Purely resonant emission features are found to be entirely fluorescence-like (v″≥6). Other RSR vibrational bands of O2 exhibit contributions of both types of emission including interferences between Raman (off-resonant) and fluorescence (resonant) amplitudes. The observed depolarization ratios also reflect these various emission characters. The RSR spectra of O2 excited by incoherent (ArF) driving fields are contrasted with that due to monochromatic excitation. Convolution of the incident spectral density with a rovibronic Kramers–Heisenberg irreducible tensor treatment of resonance Raman scattering cross sections is shown to capture all the observed RSR emission characteristics.

Relaxation of optically excited F centers

The relaxation of optically excited F centers was studied by resonant secondary radiation (RSR), which occurs successively as Raman scattering, hot luminescence and ordinary luminescence. The RSR and its linear polarization were measured as a function of excitation photon energy mainly at 77 K, for F centers in seven alkali halides. Dynamic processes, including these optical processes were analyzed in terms of a semi-classical model based on the Franck-Condon principle in an A 1g anharmonic adiabatic potential derived from the Born-Mayer potential. It is proposed that, abruptly after the optical excitation, the F electron expands its orbital radius and changes its nature including decoupling from the T 2g Jahn-Teller mode. This model works particularly for KCl, RbCl and NaCl. The relaxation of F centers in KBr and KI is different from that in KCl, RbCl and NaCl. The difference is related to the characteristic differences in lattice dynamics, namely predominant coupling with localized modes and the T 2g frequency near that of the LO phonons. The relaxation of type II F A centers is attributed to two steps, one F-like and the other Li +-dominated.

Excited-state relaxations and resonant second-order optical processes

Abstract The spectral and temporal characteristics of resonant secondary radiation have been calculated for a three-level system coupled with a reservoir. The system-reservoir interaction has been simulated by a Gaussian-Markovian energy modulation in the intermediate state. Simple intensity relations have been obtained for the secondary radiation components, which are useful to determine ultrafast relaxation parameters in the excited states of condensed phases. The calculation indicates that Raman scattering should be considered to occur, under just-resonance excitation, within a duration around the reciprocal homogeneous absorption bandwidth. This is shown to be consistent with experimental data.

A Recursion Method for Calculating Many‐Particle Green's Functions. Resonant Secondary Radiation and Excitation Spectra in the Exciton Region

AbstractA procedure for calculating many‐particle Green's functions is suggested, which is based on the information supplied by the recursion method. The advantages of the procedure are the possibility of introducing a renormalized energy spectrum of the considered system, exactly definable within the recursion method, into calculations and their relative simplicity. As an illustration of the general method a calculation of a two‐particle Green's function, describing a resonant secondary radiation in the region of a three‐dimensional isolated band of excitons interacting mainly with optical phonons, is carried out. The range of parameters covers the cases of a weak exciton‐phonon coupling and a vibronic exciton. The main attention is paid to the relation of luminescence and scattering components. The obtained spectra are compared with experimental results.

Resonant Secondary Radiation in Strongly Coupled Localized Electron-Phonon System

Numerical calculations of the resonant secondary radiation spectrum of the strongly coupled localized electron-phonon system are presented both for the stationary and transient responses. The time evolution of the transient response makes it clear how the line shape of the stationary radiation spectrum is formed in accordance with the three characteristic time-scale, namely, the phase relaxation time, the energy relaxation time and the population decay time.

Anomalied in the intensity of the resonant secondary radiation of F-centers in KCl

The resonant secondary radiation spectrum for a two-level system with strong electron-phonon coupling is calculated and compared with that observed in F-centers of KCl. It is shown that the effective transition probability from the excited to the ground state of the F-center decreases dramatically as the lattice relaxation goes on.

Theory of light-induced dephasing effects in resonance secondary radiation

Theory of light-induced dephasing effects in resonance secondary radiation