Luminescence of Eu2+ in strontium and barium thiogallates

Solid state investigation of the MSGa2S3 systems (M = Sr, Ba) gives evidence of the existence of the following thiogallates: SrGa2S4, Sr2Ga2S5, BaGa4S7, BaGa2S4, Ba2Ga2S5, Ba3Ga2S6, Ba4Ga2S7, and Ba5(GaS4)2. When substituted for the alkaline earth, Eu2+ shows an emission in most host lattices. The emission band shifts to longer wavelengths with increasing MGa atomic ratio of the host lattice. For most thiogallates, despite low phonon energies and small Stokes shifts, quenching of the Eu2+ emission starts below 300 K. Reasons for such behaviors are discussed.