Energy levels of Er3+ in LiYF4

A preliminary analysis of the absorption and fluorescence spectra of Er 3+ (4f 11 ) in LiYF 4 has been made. With the aid of previous work on Er 3+ in LaF 3 , various states have been identified. The Racah parameters giving the best overall agreement between the predicted `free ion' spectrum and the spectrum of Er 3+ :LiYF 4 are identical with those for LaF 3 , that is E 1 = 6747 cm -1 , E 2 = 31·63 cm -1 , E 3 = 635·8 cm -1 and ζ = 2345 cm -1 . An attempt has also been made to determine the nature of the crystal-field potential by considering the rare earth site as a tetragonally distorted cube. The most suitable crystal-field parameters were found to be B 2 0 = -115 cm -1 , B 4 0 = -171 cm -1 , B 4 4 = -661 cm -1 , B 6 0 = +25·5 cm -1 and B 6 4 = -168 cm -1 .