Electron-Nuclear Double-Resonance Study of the Self-Trapped Hole Associated with Lithium in NaF

Abstract

A new ESR center has been produced in NaF crystals containing lithium impurities by producing $V_K$ centers and warming the crystal to 150°K so that the self-trapped holes can migrate until they associate with the impurities. The complex consisting of the self-trapped hole associated with a ${\mathrm{Li}}^{+}$ impurity ion has been named the "$V_{\mathrm{KA}}$ center." The ESR spectrum can be interpreted in terms of a "bent-bond" $\mathrm{F}_2^{}{}_{}{}^{-}$ molecule ion. An electron-nuclear double-resonance (ENDOR) study of the $V_{\mathrm{KA}}$ center has provided definite confirmation of the assumed model. The difference in the ENDOR spectra of different ESR lines has been explained by a diagonalization of the complete spin Hamiltonian matrix which includes the hyperfine interactions of the unpaired electron with both the molecular nuclei and the lattice nuclei.