Diffusion Effects in the Inhomogeneously Broadened Case: HighTemperature Saturation of the FCenter Electron Spin Resonance
Abstract
An experimental and theoretical study is made of the effects of a random spectral diffusion process on the saturation behavior of a normally inhomogeneously broadened resonance. The random type of spectral diffusion process results, for example, if a spin diffuses on a set of sites having a distribution of local fields giving the inhomogeneous width but such that local fields at adjacent sites are uncorrelated. The calculation shows a transition in saturation properties to those characteristic of a homogeneously broadened resonance as the quantity β=ω_{D}(ω_{1}+ω_{D})ω_{1}ω_{2}^{*} approaches unity, where ω_{1}, ω_{D}, and ω_{2}^{*} represent, respectively, the spinlattice relaxation rate, the spectral diffusion rate, and the inhomogeneous width. A study of the transition behavior can yield values of ω_{1} and ω_{D} in the transition range. The analysis is shown to apply in the transition range 470 to 550°C for the KCl F center. Analysis of the transition saturation data yields a value of ω_{1} which agrees with the expression of Feldman, Warren, and Castle, which for absolute temperatures T large compared with 210°K becomes ω_{1}=3.5×10^{1}T^{2} sec^{1}. The spectral diffusion rate in zonerefined samples is given by ω_{D}=12ν_{0} exp (E_{m}kT), where ν_{0}=3.7×10^{15}×10^{+/1.2} sec^{1}, and E_{m}=1.6+/0.2 eV. The spectral diffusion is interpreted as resulting from diffusion of the F center in [110] steps of length 2a, where a is the interionic distance, with attempt frequency ν_{0} and motion energy E_{m}. This process does not account for the diffusion coefficient of the F center, which results from diffusion of ionized electrons to anion vacancies, and which is limited in the case of dense coloration by charge compensating vacancy diffusion.
 Publication:

Physical Review
 Pub Date:
 February 1966
 DOI:
 10.1103/PhysRev.142.555
 Bibcode:
 1966PhRv..142..555W