Electron nuclear double resonance of divalent thulium in calcium fluoride

An investigation of the ground state of $^{169}$Tm$^{2+}$ in CaF$_2$ has been carried out by the endor method. The positions of excited crystal field states were known accurately from the work of Kiss (1962) and with this information it was possible to obtain a value of $\mu_n = (-)0.234 $\pm$ 0.003 n.m.$ for the nuclear moment of $^{169}$Tm which may be compared with the atomic beam value of $\mu_n$ = -0.229 $\pm$ 0.003 n.m. (Ritter 1962). The hyperfine interactions of the Tm$^{2+}$ ion with the four nearest fluorine shells have been measured. Both the thulium and fluorine endor line widths were investigated at X band and at K band and the results are discussed.