Luminescence of Eu2+ in strontium and barium thiogallates

Luminescence in Sulfides: A Rich History and a Bright Future

Sulfide-based luminescent materials have attracted a lot of attention for a wide range of photo-, cathodo- and electroluminescent applications. Upon doping with Ce³⁺ and Eu²⁺, the luminescence can be varied over the entire visible region by appropriately choosing the composition of the sulfide host. Main application areas are flat panel displays based on thin film electroluminescence, field emission displays and ZnS-based powder electroluminescence for backlights. For these applications, special attention is given to BaAl₂S₄:Eu, ZnS:Mn and ZnS:Cu. Recently, sulfide materials have regained interest due to their ability (in contrast to oxide materials) to provide a broad band, Eu²⁺-based red emission for use as a color conversion material in white-light emitting diodes (LEDs). The potential application of rare-earth doped binary alkaline-earth sulfides, like CaS and SrS, thiogallates, thioaluminates and thiosilicates as conversion phosphors is discussed. Finally, this review concludes with the size-dependent luminescence in intrinsic colloidal quantum dots like PbS and CdS, and with the luminescence in doped nanoparticles.

Photoluminescence of ZnGa2S4 : Eu2+

ZnGa2S4:Eu2+ shows a light green emission at room as well as at low temperatures. The maximum of the band of the 4f65d1 → 4f7 emission is located at about 536 nm (18657 cm–1) and depends slightly on the excitation energy. The respective excitation band has a maximum at 470 nm (21277 cm–1). These results lead to the assumption that the Eu2+ ions are substituted at octahedral voids of the host lattice rather than at cationic sites. This is to be expected also because of the different ionic radii of the cations. Further emission and excitation bands are detected at higher energies in ZnGa2S4:Eu2+ as well as in undoped ZnGa2S4 which depend strongly on the respective excitation and emission energies and can, thus, be assigned to host lattice bands.