The anisotropy of the spin—lattice relaxation in the lowest triplet state of naphthalene in durene in the presence of a magnetic field

Optically detected zero-field resonance has been used to characterize the intrinsic and deep trap 3 nπ * states in single crystals of 2-benzoylpyridine at 4.2 K. The dynamic properties of these states were studied by means of time-resolved modulated phosphorescence (t. r. m. p.) and estimates for the rate constants for depopulation and spin-lattice relaxation of the magnetic sub-levels obtained by computer simulation. For all species, depopulation from ז z dominates, having rates of order 100 s -1 , but the ז x and ז y sub-states have substantial radiative activity. The orientations of the fine-structure tensors of the magnetic species were determined from high-field e. p. r. spectra. Assuming that z is parallel to C = O, excitation causes the C = O direction to change by 8 ± 2° for the intrinsic species and by an in-significant amount for the deep trap. These spectra also demonstrated that the intrinsic triplet state is mobile. This species is believed to be a polaron with slow intersite hopping rate. A maximum energy transfer rate of 10 4 -10 5 s -1 was found for transfer between translationally inequivalent sites symmetry-related by twofold rotation about the crystal b -axis. Rate estimates for transfer to the other two translationally inequivalent sites established the two dimensional nature of the polaron. The sign and shape of the zero-field resonances for the intrinsic species were found to depend on whether excitation was through S 1 or T 1 . From the parameters required to simulate the corresponding t. r. m. p. signals it is inferred that the changes are largely due to differences in the rate constants for non-radiative decay. The deep trap was shown to have an orientation and magnetic properties similar to those of the intrinsic species, and is believed to be a physical defect. It has radiative activity from the ז x sub-level which is significantly less than for the intrinsic species. Spin-lattice relaxation is fast for the mobile intrinsic species ( ca . 10 4 s -1 ) compared with the deep trap rate ( ca . 50 4 s -1 ). For the intrinsic species a field dependence for spin-lattice relaxation is apparent.

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Spin–Lattice Relaxation Rate in Organic Dirac Electron System α-(BEDT-TTF)2I3 under Strong Magnetic Field

Journal of the Physical Society of Japan ◽

10.7566/jpsj.88.054713 ◽

2019 ◽

Vol 88 (5) ◽

pp. 054713 ◽

Cited By ~ 2

Author(s):

Takehiro Tani ◽

Akito Kobayashi

Keyword(s):

Magnetic Field ◽

Relaxation Rate ◽

Strong Magnetic Field ◽

Lattice Relaxation ◽

Electron System ◽

Spin Lattice Relaxation ◽

Spin Lattice Relaxation Rate ◽

Spin Lattice ◽

Lattice Relaxation Rate ◽

Dirac Electron

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Spin-Gitter-Relaxation im Triplett-Zustand von Chinoxalin in Perdeutero-Naphthalin und zwei ähnlichen Mischkristallen

Zeitschrift für Naturforschung A ◽

10.1515/zna-1975-6-707 ◽

1975 ◽

Vol 30 (6-7) ◽

pp. 754-770 ◽

Cited By ~ 5

Author(s):

U. Konzelmann ◽

D. Kilpper ◽

M. Schwoerer

Keyword(s):

Triplet State ◽

Deep Trap ◽

Lattice Relaxation ◽

Relaxation Mechanism ◽

Mixed Crystals ◽

Spin Lattice Relaxation ◽

Relaxation Processes ◽

Shallow Trap ◽

Field Range ◽

Spin Lattice

Abstract Spin Lattice Relaxation in the Triplet State of Qainoxaline in Perdeuteronaphthalene and of two Similar Mixed Crystals The spin lattice relaxation in the excited triplet state of three mixed crystals was investigated: Quinoxaline in perdeutero-naphthalene, quinoxaline in naphthalene (X-traps) and quinoxaline in durene. They differ by the depth of their traps, which are shallow (90 cm -1), very shallow (60 cm -1) and deep (6600 cm -1), respectively. In order to identify the relaxation processes and the relaxation mechanism, the experiments were performed in the large magnetic field range be-tween 0.2 T and 5.4 T. By use of a non-resonant optical method and by ESR and ODMR it could be shown that at high fields the direct process (emission of resonant phonons) is the only efficient process up to 4.2 K. At low fields Raman-processes are dominant. Thereby the spin lattice relaxation probability per unit time, w, increases with the ninth power of the temperature in the shallow trap systems and with the fifth power in the deep trap system. By the analysis of the very strong anisotropy of w it could be shown that the efficient relaxation mechanism in the shallow trap systems is a guest-host-interaction modulated by phonons.

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