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Optical, Electrical, and ESR Studies of Additively Colored KCl Doped with Magnesium

1969; American Institute of Physics; Volume: 183; Issue: 3 Linguagem: Inglês

10.1103/physrev.183.842

1536-6065

G. D. Sootha, Devendra Singh,

Advanced NMR Techniques and Applications

The plots of ${log}_{10}\ensuremath{\sigma}T$ as a function of $\frac{1}{T}$ for the uncolored crystals of KCl doped with magnesium show the usual intrinsic and extrinsic regions. The value of the energies derived from the conductivity plot are $W=2.14$ eV for the energy of formation of a separated pair of vacancies, $E=0.75$ eV for the energy of activation for the migration of a cation vacancy, and ${W}_{a}=0.42$ eV for the energy of association of a cation vacancy with a ${\mathrm{Mg}}^{2+}$ center. These crystals give an optical absorption band peaking at 272 nm. After additive coloration, magnesium does not introduce any additional bands in the visible or ultraviolet regions of the spectrum. On optical bleaching of the colored crystals at room temperature, the usual $F$-aggregate bands are formed at the expense of the $F$ band. On heating the colored crystal above 100\ifmmode^\circ\else\textdegree\fi{}C, $F$ centers start decreasing in number and a broad optical absorption band peaking at \ensuremath{\sim}320 nm starts developing. The alkali-metal colloids are not formed in these crystals. The centers responsible for the 320-nm band are unstable above 350\ifmmode^\circ\else\textdegree\fi{}C. The centers responsible for the 272- as well as for the 320-nm bands are not paramagnetic. The conductivity ratio $\frac{{\ensuremath{\sigma}}_{c}}{{\ensuremath{\sigma}}_{n}}$, where ${\ensuremath{\sigma}}_{c}$ is the conductivity of the colored crystal and ${\ensuremath{\sigma}}_{n}$ that of an identical uncolored crystal, remains less than unity from 100 to 600\ifmmode^\circ\else\textdegree\fi{}C.