4fn→4fn-15d transitions of the light lanthanides:: Experiment and theory -: art. no. 045113

The 4f(n)-->4f(_n-1)5d(fd) excitation spectra of the light lanthanides (Ce3+, Pr3+, Nd3+, Sm3+, and Eu3+) incorporated in LiYF4, CaF2, and YPO4 are investigated in the ultraviolet and vacuum-ultraviolet spectral region (100-250 nm). In these host lattices fine structure (zero-phonon lines and vibronic lines) is observed for fd transitions involving the lowest 5d crystal-field state. The observation of zero-phonon lines makes it possible to analyze the complicated structure in the fd spectra and to compare the experimentally observed spectra with energy-level calculations for the 4f(n-1)5d states. Energy-level and intensity calculations were performed by an extension of the commonly used theory for energy-level calculations of 4f(n) states. A good agreement between experiment and theory is obtained for the overall structure using the crystal-field splitting (from the spectra of Ce3+), the parameters for the splitting of the 4f(n-1) core (from the literature on energy level calculations for 4,f(n) states) and the spin-orbit coupling of the 5d electron and Coulomb interaction between 4f and 5d electrons (from atomic parameters using the computer code of Cowan).