4fn↔4fn−15d transitions of the trivalent lanthanides: experiment and theory

Emission and excitation spectra of 4fn↔4fn−15d transitions of lanthanide ions in LiYF4 are reported and are succesfully reproduced by energy level calculations using a theoretical model that extends established models for the 4fn configuration to include fd states. Some interesting trends are observed. Lifetime measurements for the spin-allowed fd emission show that the electric dipole matrix element for the fd transition decreases through the lanthanide series. Also the splitting between the high spin and low spin fd states decreases through the lanthanide series. Both effects are reproduced by our model.