Abstract
Optical absorption and paramagnetic resonance of KCl crystals containing preferentiallyR-centers have been studied during and after excitation with 430 mμ or 365 mμ light at 90 °K. A partly metastable, partly stable state has been detected and identified as the quartet state of theR-center, which proves to be an association of threeF-centers forming an equilateral triangle in the (111) plane of the crystal as proposed byvan Doorn andHaven andPick. — The crystals used were additively colored to 6.6·1017 F-centers/cm3 and illuminated withF-band light at room temperature until theR/M-ratio reached its maximum value. During light excitation the optical spectrum in the region of theR-bands shows characteristic small changes. A part of these changes disappears spontaneously with a time constant τ=14.5 sec when the light excitation is removed (“temporary bleaching”). The remaining part has a similar spectral distribution. It is completely stable in the dark, but can be bleached within a few seconds by illumination with 840 mμ light. — Electron spin resonance of the crystal under light excitation shows in addition to theF-center line a seven-line spectrum with strong angular dependence, if the field is rotated in a (110) plane. The maximum splitting is 674 G, the width of the individual lines 35.5 G. The angular dependence of the spectrum can be fitted to a fine-structure spin Hamiltonian
withg=1.996,D/g μ B=+168.5 G,S=3/2 and thez-axis in any of the four 〈111〉 directions of the crystal. After switching off the excitation light the seven-line spectrum decays with the same time constant as the optical changes to a stable level of approximately 20% which can be destroyed by illumination with 840 mμ light. (ΔM=2)-transitions are expected on the basis of the above Hamiltonian and have been observed. — In the ENDOR spectrum the lines of theK Iα nuclei which are nearest neighbours to the threeF-centers of theR-center have been analysed. Their hyperfine interaction is purely isotropic witha/h=17.85 Mc/sec. — General expressions are derived for fine structure and hyperfine structure of the (S=N/2)-state of anN-electron center with negligible spin-orbit coupling. The hyperfine interaction of the nucleusK Iα is very well understood on the basis of an Heitler-London approximation of theR-center. For the fine structure the Heitler-London approximation using the known fine structure of theM-center triplet state predicts a value ofD which is roughly a factor of 2/3 too small. The mechanisms of excitation and decay between the doublet ground state and the quartet state of theR-center are not yet understood.
Article PDF
Similar content being viewed by others
Avoid common mistakes on your manuscript.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Seidel, H., Schwoerer, M. & Schmid, D. Der Quartett-Zustand desR-Zentrums in Kaliumchlorid-Kristallen. Z. Physik 182, 398–426 (1965). https://doi.org/10.1007/BF01383119
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF01383119