The light-emission and photophysical properties of CsCaCl3:Tm2+ (1.04%), CsCaBr3:Tm2+ (0.48%), and CsCaI3:Tm2+ (0.76%) are presented. We find that Tm2+ is a multiple emitter under 21,834 cm-1 laser excitation at low temperatures in all three compounds. Several distinct types of emission are observed and characterized: sharp and long-lived 4f-4f emission in the infrared (IR) and up to four broad and fast decaying emission bands in the near-IR and visible, originating from the 4f-5d states of Tm2+. The optical spectroscopic properties of the samples are compared, and we find that the measured differences in the relative intensities and the shifts in the position of the emissions can be related to the chemical influence on the absorption and emission properties of Tm2+. Thus, it nicely illustrates the principle of chemical variation on the optical spectroscopic properties. An investigation of the temperature dependence of the luminescence yields important information about the dynamics of the excited states. The interplay and competition between radiative and nonradiative pathways is explained and modeled using a single configurational coordinate approach.

Spectroscopic and crystallographic data are presented for salts containing the [V(OH(2))(6)](3+) cation, providing a rigorous test of the ability of the angular overlap model (AOM) to inter-relate the electronic and molecular structure of integer-spin complexes. High-field multifrequency EPR provides a very precise definition of the ground-state spin-Hamiltonian parameters, while single-crystal absorption measurements enable the energies of excited ligand-field states to be identified. The EPR study of vanadium(III) as an impurity in guanidinium gallium sulfate is particularly instructive, with fine-structure observed attributable to crystallographically distinct [V(OH(2))(6)](3+) cations, hyperfine coupling, and ferroelectric domains. The electronic structure of the complex depends strongly on the mode of coordination of the water molecules to the vanadium(III) cation, as revealed by single-crystal neutron and X-ray diffraction measurements, and is also sensitive to the isotopic abundance. It is shown that the AOM gives a very good account of the change in the electronic structure, as a function of geometric coordinates of the [V(OH(2))(6)](3+) cation. However, the ligand-field analysis is inconsistent with the profiles of electronic transitions between ligand-field terms.

Variable-temperature spectroscopic and crystallographic studies on the chromium(II) Tutton's salts, (MI)2Cr(X2O)6(SO4)2, where MI = ND4+, Rb+, or Cs+, and X = H or D, are reported. Inelastic neutron scattering (INS) and multifrequency EPR experiments facilitate a rigorous definition of the ground-state electronic structure from 1.5 up to 296 K, which is unprecedented for a high-spin d4 complex. Modeling of the INS data using a conventional S = 2 spin Hamiltonian reveals a dramatic variation in the axial and rhombic zero-field-splitting parameters. For the ammonium salt, D and E are -2.454(3) and 0.087(3) cm(-1) at 10 K and -2.29(2) and 0.16(3) cm(-1) at 250 K, respectively. A temperature variation in the stereochemistry of the [Cr(D2O)6]2+ complex is also identified, with an apparent coalescence of the long and medium Cr-O bond lengths at temperatures above 150 K. The corresponding changes for the rubidium and cesium salts are notable, though less pronounced. The experimental quantities are interpreted using a 5Ee Jahn-Teller Hamiltonian, perturbed by anisotropic strain. It is shown that good agreement can be obtained only by employing a model in which the anisotropic strain is itself temperature dependent. A new theoretical approach for calculating variable-temperature EPR spectra of high-spin d4 complexes, developed within the 5Ee coupling model, is described. Differences between spin-Hamiltonian parameters determined by INS and EPR are consistent with those of the different time scales of the two techniques.