In this paper, double resonance signals associated with CW spectral ho
leburning measurements of unintentional Ho3+ impurities in crystals of
YLiF4 are reported. The double resonance signals are detected in the
microwave and radiofrequency region, The observed microwave resonances
are at 4.460(1) and 4.473(1) GHz and attributed to ground state hyper
fine splittings. Two radiofrequency resonances at 29.85(8) and 36.86(8
) MHz are also detected and assigned to superhyperfine transitions of
the two inequivalent fluorine nn sites. This assignment is supported b
y Zeeman measurements.