Spin-Lattice Relaxation ofFCenters in KCl: IsolatedFCenters

F centers in LiF: A nuclear magnetic resonance study

“…As discussed for the background relaxation, this corresponds to an increase of t À1 e / T 8:4 , in reasonable agreement with the behavior expected for a Raman process [10]. At temperatures T > 20 K, the temperature dependence of T 1 becomes weaker (T À1 1 / T 0:43 ), which corresponds to a t À1 e / T 1:7 -law for the F center dynamics.…”

“…electrons at an empty anion site, are formed relatively easily. F centers in alkali halides have widely been studied over the last fifty years [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] by optical absorption spectroscopy, nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR), and other techniques. As these studies have shown, the F center EPR spectra show orientation dependent hyperfine splittings due to the interaction with the neighboring lithium and fluorine atoms.…”

Magnetic resonance investigation of the dynamics of F centers in LiF

“…assuming that a direct process occurs at temperatures below 4 K [14]. For the sample irradiated with 126 kGy g-rays, one obtains T 1e 4:2 K 196 ms: The density N F of the F centers is 6.6 £ 10 17 cm 23 .…”

“…The background contribution visible in the other two samples is largely eliminated in these data. The weaker temperature dependence of the sample with higher F center concentration at lower temperatures can be explained by the theory of Warren, Feldman and Castle [12,14]. If the sample is heated above 360 K, an annealing process sets in that reduces the number of F centers and other defects.…”

“…(2) 1=T 1n / T 21=4 1e / T 1=2 is in good agreement with the experimental ®ndings. At low temperatures, one has T 1e / T n with n 7 or 9 depending on the kind of mixing of the Kramers states [14] Then, by use of Eq. (2) one expects 1=T 1n / T m with m 1:75±2.25 which deviates remarkably from the observed exponent m 3:7 : We suppose that the interaction among the F centers at low temperatures gives rise to the observed enhancement of m, i.e.…”