Photoluminescence characteristics of BaS:Eu,Dy and the mechanism affected by S-related defects

BaS:Eu,Dy phosphors were prepared by high temperature solid-state method with BaSO4 as matrix raw material, Eu2O3 and Dy2O3 or Eu2(SO4)3·8H2O and Dy2(SO4)3·8H2O as doped ion raw materials. BaSO4 can be completely reduced after 3 h sintering at 1200 °C in CO atmosphere and pure BaS was obtained in one step. Meanwhile, the rare earth ions were embedded in the host lattices and had no impact on the main structure of the products. However, X-ray diffraction peaks shift shows rare earth doping can cause lattice distortion with the increase of sintering temperature. The luminescence characteristics of BaS:Eu,Dy, BaS:Eu, BaS:Dy and BaS are compared in order to study the luminescence mechanism. It is confirmed that the broad emission locating in the near-infrared (NIR) region should be assigned to 4f65 d1→4f7 transition of Eu2+, and the emission locating in the visible region comes from S-related defects in the matrix. Sulfur-rich is particularly detrimental to NIR luminescence. In relatively S-rich systems, there is serious energy transfer between Eu2+ and S-related defects, which leads to fluorescence quenching. The products are in S-rich state when Eu2(SO4)3·8H2O and Dy2(SO4)3·8H2O are selected as raw materials of doped ions. BaS:Eu,Dy inclines to emit visible light with the sintering temperature increasing. By contrast, the products are in Sulfur-deficiency state when Eu2O3 and Dy2O3 are used as raw materials of doped ions and BaS:Eu,Dy only gives NIR emission.