Luminescence, raman and absorption spectrophotometric studies of selected lanthanide and actinide compounds in the solid state

Raman, absorption and luminescence spectroscopy has been used extensively in our laboratory to recognize crystal structures or to identify changes in the structural pattern of solid compounds at different temperatures and pressures. These techniques have also been employed to determine the chemical environment of f element ions in different compounds and solutions. Polarized Raman spectroscopy was used to assign the Raman-active bands of selected lanthanide oxyhalide single crystals. Cerium oxychloride was synthesized for the first time in the present research. The polarized luminescence, absorbance and electronic Raman spectra from single crystal europium oxychloride, recorded at 300 and 77 K, were measured, interpreted, and used to calculate crystal field parameters. Although a suitable UV excitation source was unavailable, luminescence from the upper levels was obtained by resonance enhanced two-photon excitation. The same techniques were applied to both a collection of coaxial single crystals and polycrystalline europium oxychloride under pressure using a diamond anvil cell. The spectra at high pressure suggest the presence of Eu¹¹ ion. The two-photon sequential excitation technique was also employed, for the first time, to study the electronic levels of Cm¹¹¹ and Cf¹¹¹ in trihalides. Such luminescence is often weak due to an efficient nonradiative de-excitation process due to closely spaced energy levels. Nevertheless, because of the low background encountered in two-photon processes, the energy of many levels can be obtained. These energy values were used to determine ion site symmetries and in some cases to calculate crystal field parameters. The effect of pressure on the Raman, absorption and luminescence spectra of CmCl₃ was investigated. The curium trichloride behavior was compared to previous studies on lanthanide trihalides and along with new studies on NdBr₃ to confirm the possibility of a new high pressure phase.