The 5d←4f excited states of [Ce(OH₂)₉]³⁺

Abstract

Five absorption bands of the allowed 5d←4f transitions of Ce³⁺ were detected in the ultraviolet region between 37 and 51 × 10³ cm^-1 by σ- and π-polarized absorption, luminescence excitation, and MCD spectra with the single crystals of Ce³⁺ doped lanthanum ethylsulphate enneahydrate. In the crystal, Ce³⁺ is in a D _3h ligand field of nine water molecules such as in [Ce(OH₂)₉]³⁺.

Two resolved luminescence bands detected in 30 and 32 × 10³ cm^-1 at liquid nitrogen temperature are assigned to the transitions to the ² F _5/2 and ² F _7/2 substates of the ground ² F(4f ¹) state split by the spin-orbit coupling of a cerium 4f electron. On the other hand, the five absorption bands are assigned to five Kramers doublets of excited ² D (5d ¹) state split by the ligand-field interaction and the spin-orbit coupling of a cerium 5d electron.

A greater Stokes shift between absorption and emission maxima observed in the crystal indicates a destabilization of the coordination bonds in the excited state.