Dynamics of nuclear wave packets at theFcenter in alkali halides

Abstract

The F center in alkali halides is a well-known prototype of a strongly coupled localized electron-phonon system. This colour center is one of the long studied targets in the field of photophysics because it is simple but rich in variety. Steady-state spectroscopy, such as modulation spectroscopy and Raman scattering spectroscopy, has elucidated the strength of the electron-phonon coupling in the (meta-)stable state, i.e. the ground state and the relaxed excited state. Picosecond spectroscopy has improved understanding of the state mixing in the transient state. Owing to recent developments of ultrafast lasers with pulse widths shorter than oscillation periods of phonons, it has been possible to perform real-time observation of lattice vibration, and the understanding of the transient state has been remarkably expanded. In this paper, we review early and present studies on dynamics of electron-phonon coupling at the F center, especially recent real-time observations on the dynamics of nuclear wave packets in the excited state of the F center in KI, KBr, KCl and RbCl. These real-time observations reveal (i) spatial extension of the electronic wave function of a trapped electron, (ii) the difference between the coupled phonons in the ground state and the excited state, (iii) diabatic transition between the adiabatic potential energy surfaces and (iv) anharmonicity of the potential energy surface.

Layer number dependence of carrier lifetime in graphenes observed using time-resolved mid-infrared luminescence

“…Samples were excited from the top of the sample on the substrate over a diameter of approximately 200 m at 1.57 eV (790 nm), by 100 fs pulses at a repetition rate of 200 kHz. The infrared luminescence signal was up-converted to visible light by mixing with 1.57 eV gating pulses in an optical nonlinear LiIO 3 crystal, analyzed by a double grating monochromator (f=18 cm), and detected with a photon counting system [19]. To cut the visible luminescence from the sample, we placed a red thin film or a high resistivity Si plate before the nonlinear crystal for measurements at low or high photon energies, respectively.. We estimated the time resolution measuring the pulse width of sum frequency waves between the gating pulse and the Rayleigh scattering pulse from the sample surface (cross correlation method) using the same nonlinear crystal (LiIO 3 ).…”

First principles calculations of optical properties for oxygen vacancies in binary metal oxides

“…8,16 We note that the dynamics of similar PL of F centers in alkali halides has been studied in detail. 43 In that case, the transition is allowed due to mixing of 2s and 2p terms, with 2s having the lower energy in the relaxed excited state. 43 To shed more light on the nature of excited states, we have calculated the triplet excited states of the V 0 O center in MgO using the so-called ∆SCF method.…”

“…43 In that case, the transition is allowed due to mixing of 2s and 2p terms, with 2s having the lower energy in the relaxed excited state. 43 To shed more light on the nature of excited states, we have calculated the triplet excited states of the V 0 O center in MgO using the so-called ∆SCF method. This computational procedure employs a non-Aufbau occupation of the triplet state in a dielectric to converge the KS equations to an excited state.…”

Optically detecting the edge-state of a three-dimensional topological insulator under ambient conditions by ultrafast infrared photoluminescence spectroscopy

“…Ultrafast infrared photoluminescence spectroscopy was performed with the up-conversion technique34353637 in air at room temperature. The TlBiSe 2 sample was excited using 70 fs pulses at a wavelength of 800 nm (1.55 eV) from a Ti:sapphire regenerative amplifier operating at a repetition rate of 200 kHz.…”