Observation of Eu2+ in Y2O2S:Eu3+ and Y2O2S:Eu3+, Tb3+

Europium(II) has been observed in Y2O2S:Eu3+ and Y2O2S:Eu3+,Tb3+ phosphors by ESR spectroscopy. It is notable that the intensity of the ESR peaks corresponding to Eu2+ is increased when terbium ion is incorporated, which may be explained partially by the redox mechanism. According to the energy level considerations, the energy state of Eu2+ is above the Fermi level of the Y2O2S lattice. Hence, the Eu2+ valence state is unlikely to exist in Y2O2S. Europium(II) may exist as EuS in our sample. Intensity of photoluminescence of Y2O2S:Eu3+(4%),Tb3+(0–1.3%) is decreased as the concentration of Tb3+ increases. Decrease in the intensity of charge transfer band in the excitation spectra is more severe compared with the decrease in the intensity of the peaks of f-f transition.