Satellite Lines Due to Ion-Pairs in the Luminescence Spectra of Y2O2S:Eu3+

In the luminescence spectra of the 5 D 0 → 7 F 1 transition of Y 2 O 2 S:Eu 3+ , satellite lines separated from the main lines by several cm -1 were observed. Under the excitation by 365 mµ radiation, the intensity of the main line increases linearly with the concentration of Eu 3+ , whereas that of the satellite lines increases as the 1.36 th power of the concentration. When Gd 3+ is codoped in Y 2 O 2 S:Eu 3+ keeping the concentration of Eu 3+ constant, the intensity of the satellite lines relative to the main line increases with the concentration of Gd 3+ . It is concluded that the satellite lines originate from the splitting and shift of the crystalline-field components resulting from a slight lattice distortion around a pair of Eu 3+ ions or that of an Eu 3+ ion and a Gd 3+ ion which occupy two nearest cation sites.