IR photoconductivity of C60 fullerene single crystals

Plastic-strain induced peaks in the spectrum of F-light-stimulated photoconductivity in colored NaCl crystals

“…Indeed, the dislocation electrons play an important role in the photoplastic effect, i.e., in the increase of the deforming stress caused by illumination of colored alkali-halide crystals [7]. Investigations of the photoplastic effect in alkali-halides by the dislocation internal-friction technique revealed two principal mechanisms of the dislocation drag [8][9][10][11][12]. In the first mechanism, electrons released from F-centers are captured by different electron traps in the specimen bulk, thus forming photo-induced pinning centers that prevent the dislocation motion and lead to hardening of the crystal.…”

Enhanced thermoelectric performance by resonant vibrational mode-selective density-of-states distortions

“…+ H dipole ), which describes the light-coupled component of the interacting material-radiation field system, is composed of the Hamiltonians of the interacting radiation field and the electric dipole moment of the radiative transition, given in the dipole approximation as: [50][51][52] state energies, g ðiÞ os is the linear coupling between the radiation field and the local electron density (i.e., n j ¼ c y 2ð2Þ c 2 ), M (i) s is the electric dipole matrix element associated with the transition between the two electronic levels, c y 1ð2Þ and c 1(2) are the creation and annihilation operators for a hole in electronic levels 1 and 2, a y j and a j are the creation and annihilation operators for a phonon with transition frequency o (i) s = (e 2 À e 1 )/h , N s is the total number of modes in the laser cavity associated with the modulation frequency o (i) s , the subscript s denotes the particular vibration mode that is excited, and the superscript i denotes whether or not this vibration mode is an intramolecular mode (i = 1) or an intermolecular mode (i = 2). In what follow, we only consider modulation frequencies o s that are tuned to the characteristic frequency of an intramolecular C-C stretching vibration o 0 = 215 meV (which is an optical vibration mode), [23][24][25]38,53,57,58 and drop the superscript i.…”

“…, ), M ( i ) s is the electric dipole matrix element associated with the transition between the two electronic levels, and c 1(2) are the creation and annihilation operators for a hole in electronic levels 1 and 2, and a j are the creation and annihilation operators for a phonon with transition frequency ω ( i ) s = ( ε 2 − ε 1 )/ ħ , N s is the total number of modes in the laser cavity associated with the modulation frequency ω ( i ) s , the subscript s denotes the particular vibration mode that is excited, and the superscript i denotes whether or not this vibration mode is an intramolecular mode ( i = 1) or an intermolecular mode ( i = 2). In what follow, we only consider modulation frequencies ω s that are tuned to the characteristic frequency of an intramolecular C–C stretching vibration ω 0 = 215 meV (which is an optical vibration mode), 23–25,38,53,57,58 and drop the superscript i .…”

“…Here, we adopt a well-established model for the formation of Dirac-delta-like distortions in DOS tails by the optical excitation of vibrational modes 50–56 and use it to study the thermoelectric properties of the prototypical soft organic material rubrene in the presence of infrared (IR) light that couples to valence electrons via resonant IR-active vibrational modes. 23–25,38,57,58 The results suggest that DOS distortions caused by the IR stimulation of C–C stretching vibrations in rubrene could lead to dramatic improvements in the thermoelectric PF in tail states, akin to those that result upon introducing resonant dopants to enhance PF within the band. 9,10 This resonant enhancement of PF, while induced by photo-excitation, is distinct from the photogeneration of carriers associated with Holstein small polaron formation 53–56,59 and the Photo-Seebeck effect, 60,61 and instead is shown to occur via a resonant four-step intramolecular charge transfer process that facilitates both charge delocalization and the creation of resonant DOS distortions near the intrinsic Fermi level position.…”