The determination of the energy of the Γ7state of Dy3+on cubic sites in CaF2using EPR

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Abstract
For calculations of orbit-lattice parameters for Dy3+ on cubic sites in CaF2 a very precise value of the energy Delta of the Gamma 7, first excited, state is required. A precise determination has been made using two methods. Off diagonal matrix elements of the Zeeman interaction HZ cause anisotropy in the EPR of the Gamma 7 state. From measurements at about 36 and 61 GHz, Delta =8.9(2) cm-1. The off diagonal matrix elements of HZ also cause a splitting of the +or-3/2 from or to +or-1/2 transitions of the Gamma 8 quartet. From this splitting at the two frequencies, Delta =8.3(2) cm-1. The incompatibility of these two precise determinations of Delta casts considerable doubt on the reliability of the frequently used method of determining the energies of excited states using small effects in EPR produced by small admixtures of these states.