Electron spin echo spectra and characterization of electronic ground states for lanthanide ions in acidic water:ethanol glasses.

X-band EPR absorption spectra were obtained by field-swept echo-detection for 10 mM Ce3+, Nd3+, Sm3+, Tb3+, Er3+, Tm3+, and Yb3+ in glassy acidic 1:1 water:ethanol at 4.2 to 6 K. The slowly-varying signals extend over thousands of gauss and are more readily detected by spin echo than by continuous wave EPR. For lanthanide ions spin-orbit coupling is strong and J is a good quantum number. The microwave power required to achieve a π/2 pulse depends on quantum numbers J and mJ and the gJ for the levels involved in the EPR transition, so it can be used to characterize the electronic ground state. For Nd3+, Sm3+, Er3+, and Tm3+ the power required for a π/2 pulse is consistent with values calculated for the expected value of gJ and transitions involving mJ = ±1/2 or mJ = ±1,0. However for Ce3+, Gd3+, Tb3+, and Yb3+ the microwave power required for a π/2 pulse is larger than predicted. For Ce3+, Tb3+, and Yb3+ it is proposed that mixing of levels results in contributions to the transitions from higher values of mJ. For Gd3+ the discrepancy is attributed to overlapping transitions with varying values of mJ.