Superhyperfine structures of the relaxed excited state of the F centers in KCl observed by zero-frequency optical detection of electron-nuclear double resonance

The superhyperfine (shf) spectrum of the relaxed excited state (RES) of the F centers in KCl has been observed by detecting decrement dips of the quantum efficiency eta(F) of the F luminescence in its dependence on the magnetic field B below 0.31 T at 4 K. This method is called zero-frequency optical detection of electron-nuclear double resonance (ZF-ODENDOR) described earlier by the Jaccard group. The shf spectrum depends on the angle Phi between B and the crystalline axis. From curve-fitting analysis of its Phi dependence, the isotropic and anisotropic shf interaction constants (a and b) of the RES are determined up to the 32nd shell as a function of rho being the shell distance from an anion vacancy divided by a lattice constant. From the rho dependence of the a values, the envelope wave function (EWF) of the RES is estimated as a \2s]-like EWF admired with a small fraction (13%) of \2p]-like EWF (Began and Fitchen's model). The amplification factors A(+) = 819 and A(-) = 950, and an orbital extension constant eta = 0.65 for the EWF are adopted. Thus, the advantage of the vibronic model of the RES, that is theoretical extension of Began and Fitchen's model, is supported. The rho(-3) dependence of the b(1) values is confirmed in the range rho>3.5.