HOST CATION EFFECTS ON FLUORESCENCE SPECTRUM OF EU3+ IN OXYSULFIDES

Fluorescence spectra of M2O2S:Eu3+ (M=Lu, Y, Gd, La) are investigated in the 4000-9000-Å region. Nearly complete identification of the crystal components of 7F0-6, 5D0-3 is made, and the results are interpreted by means of intermediate-coupling and crystal-field splitting calculations. A rise of the barycenters of 5DJ, as well as a contraction of the over-all crystal splitting of 7FJ and 5D J with increasing host cation size, accounts for the blue shift of the fluorescence spectrum in the above series. The results can be qualitatively understood as an approach to the free Eu3+ ion, but quantitative interpretation remains obscure.