Raman Spectra for Eu Doped Ln2O2S Phosphors

Raman spectra for Ln 2 O 2 S: Eu (Ln=Lu, Y, Gd and La) have been measured at room temperature. The observed four Raman lines are divided into low and high-frequency groups, each consisting of A 1g and E g modes in representations of D 3d crystal point group. The high-frequency lines shift toward low frequency with increasing unit cell volume, and the low-frequency lines decrease in frequency with increasing crystal mass. The Raman active modes are assigned as even vibrations of the Ln 2 O 2 parallelogram in the unit cell on the basis of the factor group analysis, The Raman lines shift continuously with increasing Eu concentration in Y 2(1- x ) Eu 2 x O 2 S and no additional mode appears. This fact indicates that the mixed oxysulfide crystal is not a mixture of the lattices of its components, but a unique lattice.