Electronic Structure of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>F</mml:mi></mml:math>Centers: Saturation of the Electron Spin Resonance

TLDR

The study aims to provide expressions that bypass Kramers‑Kronig relations for saturable electron spin resonance systems. The authors derive these expressions specifically for systems where only absorption saturates, avoiding the use of Kramers‑Kronig relations. They show that the unusual saturation of F‑center ESR in KCl, NaCl, and KBr arises from electron–nuclear interactions, measure a spin‑lattice relaxation time of 2.5 × 10⁻⁵ s at room temperature, and demonstrate that Kramers‑Kronig relations are not applicable to saturated systems.

Abstract

It is shown that the unusual observed saturation behavior of the microwave electron spin resonance associated with $F$ centers in KCl, NaCl, and KBr crystals can be accounted for if the overall width is ascribed to interaction between the $F$-center electrons and the nuclear magnetic moments of the ions adjacent to the $F$ centers. The measured saturation factor gives for $F$ centers in KCl a spin-lattice relaxation time of 2.5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}5}$ sec at room temperature. The observed saturation behavior in which only the absorption saturates is in marked disagreement with the Kramers-Kronig relations. However it is shown, that the Kramers-Kronig relations are not applicable to saturated systems. Expressions which avoid the use of these relations are presented for saturable systems.