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

A new ESR center has been produced in NaF crystals containing lithium impurities by producing VK 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 Li⁺ impurity ion has been named the "VKA center." The ESR spectrum can be interpreted in terms of a "bent-bond" F₂^_^- molecule ion. An electron-nuclear double-resonance (ENDOR) study of the VKA 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.