POLARIZATION DEPENDENCE OF 2-PHOTON EXCITATION-SPECTRA IN THE S-8(7 2)-]P-6(7/2), P-6(5/2), AND P-6(3/2) TRANSITION REGIONS OF GD3+ IN (C4H4O5)(3)]CENTER-DOT-2NACLO(4)CENTER-DOT-6H(2)O/

The relative intensities and polarization properties of two-photon abs orption (TPA) transitions are examined throughout the S-8(7/2) --> P-6 (7/2), P-6(5/2), and P-6(3/2) excitation regions of Gd3+(4f(7)) in sin gle crystals of Na-3[Gd(oda)(3)] . 2NaClO(4) . 6H(2)O (where oda denot es an oxydiacetate ligand of chemical formula C4H4O52- = (OOCCH2OCH2CO O-)-O--). In these crystals the Gd3+ ions are located at sites of D-3 point symmetry, and the Gd(oda)(3)(3-) coordination complexes have chi ral, tris-terdentate chelate structures. These crystals exhibit natura l optical activity, and they differentially absorb left- and right-cir cularly polarized light in both one-photon and two-photon excitations of the Gd3+ 4f --> 4f (intraconfigurational) electronic transitions. I n the present study, results are reported for fluorescence-detected TP A measurements performed under three different excitation polarization conditions: left-circularly polarized, right-circularly polarized, an d linearly polarized. In each case, excitation was with a single beam of laser radiation directed along the unique axis of a uniaxial single -crystal sample. The results include relative intensities and polariza tion properties determined for transitions to each of the nine Stark l evels split out of the P-6(7/2), P-6(5/2), and P-6(3/2) multiplets of Gd3+ (4f(7)). Experimental measurements are analyzed in terms of a mod ified Judd-Pooler perturbation model that explicitly incorporates spin -dependent interaction terms. Calculated versus experimentally determi ned ratios of circularly polarized to linearly polarized transition in tensities are used as a diagnostic of the efficacy of the various calc ulational methods in rationalizing the experimental results. The calcu lations show some modest success in reproducing many of the qualitativ e features of the experimental results, but they fail to account for m any of the quantitative details.