The fine spectral structures of pair and quartet centers of Nd ions in crystals were investigated by using selective laser absorption saturation and time-resolved pump/probe techniques at 8 to 30K. Spectral hole–antihole pairs were observed under laser excitation of the pair Nd ions. The main absorption lines reflected a splitting of the lowest Stark level of the 4G5/2 state, caused by a strong coherent interaction between Nd ions in clusters with total splitting values of 2.4 and 3.3/cm for pair and quartet centers, respectively. An energy diagram, including singly- and doubly-excited states, was built up for a strongly coherent interacting pair.

Fine Level Splitting of Aggregate Neodymium Centers in CaF2 Crystals. V.V.Fedorov, W.Beck, T.T.Basiev, A.Y.Karasik, C.Flytzanis: Chemical Physics, 2000, 257[2-3], 275-81