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Photoionization Analysis on Phosphors
Published in Ru-Shi Liu, Xiao-Jun Wang, Phosphor Handbook, 2022
There is no doubt that the photoconductivity experimental technique is very convincing to demonstrate photoionization and thermally assisted photoionization. However, some disadvantages still exist, including the constraint on the sample form (only single crystal or ceramics), the need to make electrodes and to apply high voltage. If it is possible to detect the photoionization process by a contactless method for powder samples, it will become a good alternative experimental way. One of the alternative ways is to measure the thermoluminescence (TL) excitation (TLE) spectrum. TL is caused by detrapping of charges that were previously trapped followed by recombination on a luminescent center. Charge trapping occurs when electrons in the excited state of luminescence centers are transferred to the CB (e.g., through autoionization or thermal ionization) and then captured by traps in the host. By measuring the TL intensity as a function of the charging wavelength, a TLE spectrum is obtained that provides information on the threshold energy of the photoionization. The attempt to determine the energy-level location with respect to the host CB using TL technique was first reported in Y2O2S:Tb3+ by Amiryan in 1977 [51] and then have been studied actively by some research groups [52–54] from the 2000s.
Explicit Approach to N-D Dynamics
Published in Thomas C. Weinacht, Brett J. Pearson, Time-Resolved Spectroscopy, 2018
Thomas C. Weinacht, Brett J. Pearson
The decay of a doubly excited state can be considered a consequence of the coupling between bound and continuum states: the interaction between the two electrons couples the bound, doubly excited state of the atom to a state corresponding to an atomic ion and a continuum electron. In this framework, autoionization is similar to spontaneous emission from an excited atom. In spontaneous emission, there are two states that are uncoupled in the absence of an atom-field interaction: the first state corresponds to an excited atom with no photons in the field, while the second state has an unexcited atom with one photon in the field. The unavoidable coupling between the atom and the field leads to what looks like a decay of a bound state to the continuum with the emission of a photon.
X-Ray Lasers
Published in Shalom Eliezer, Kunioki Mima, Applications of Laser–Plasma Interactions, 2008
Hiroyuki Daido, Tetsuya Kawachi, Kengo Moribayashi, Alexander Pirozhkov
Here, we show atomic processes used in this study. We employ x-ray absorption ionization (AI), radiative transition (Ar), autoionization (Aa), and electron impact ionization (EII) processes. Here the electrons used in Equation 4.7 are produced through the processes of photoionization absorptions and autoionization. Their energies are decided by the processes. As mentioned in Ref. [36], this process plays a role in the increase in population of the lower states, that is, decrease in the gain values. The atomic data for AI, Ar, and Aa employed here have often been calculated using an atomic data code such as Cowan’s code [51]. On the other hand, those for EII have been calculated using Lotz formula [52] or BEB theory [53].
Attoclock revisited on electron tunnelling time
Published in Journal of Modern Optics, 2019
C. Hofmann, A. S. Landsman, U. Keller
Attosecond photo ionziation delays in atoms have been first measured in the tunnel ionization (14) and then in the single-photon ionization regime (53). More detailed measurements and theory confirmed that in the simplest case, when the electron is promoted into a flat (non-resonant) continuum by direct single photon ionization, the corresponding ionization delay is then given by the Wigner delay, which can be expressed as the energy derivative of the scattering phase and is equivalent to the group delay of the departing electron wave packet (9), see also (2). To date different attosecond techniques have confirmed this result taking into account a measurement induced delay (54–56). This is in contrast to the tunnel ionization where our experimental results do not correspond to the Wigner delay because the center of wave packet makes a phase jump when a chirped wave packet propagates with an energy filter (10–12, 15) (see Section 1). In this case we loose the direct link to the classical trajectory with the centre of the electron wave packet following the Ehrenfest's theorem (41). However, with a flat continuum we do not have such an energy filter and ionization delay is correctly described by the Wigner delay. The situation becomes more complicated when ionization occurs in the vicinity of autoionizing states which significantly affect the Wigner delay (10, 11). This was further confirmed most recently with angle and spectrally resolved measurements where we could demonstrate in collaboration with Anne L‘Huillier that not only the phase of the photoelectron wave packet is significantly distorted in the presence of these autoionization resonances in argon, but that this distortion also depends on the electron emission angle (57). In this situation again we loose the direct link between the Wigner delay and the classical trajectory of the liberated electron.