LUMINESCENCE OF Bi 3+ and Eu 2+ DOUBLE CENTERS DOPED IN CaS HOST

In this work, double-center-doped luminescent material CaS:Bi3+, Eu2+ was made via flux NH4Cl by sintering in excess sulfur environment. The sample had a purplish red net luminescent color. Excitation spectra at both red, 650 nm and blue, 487 nm were taken. The red emission from Eu2+ center was mainly come from the 4f65d1 absorption in the CaS host. The blue emission from the Bi3+ center on the other hand showed no big difference from the singly doped CaS:Bi3+ materials in excitation spectrum. Emission spectra were obtained at excitaton of 270 nm and 300 nm. Stokes shift was moved about 20-30 nm, under different point excitation. Emission peaks of both Bi3+ and Eu2+ centers appeared at 463 nm, 642.5 nm by 270 nm excitation and 487 nm, 620 nm by 300 nm excitation respectively. After-glow decay curves were also obtained and the shapes of decay curves are similar and it is due to the single hole-trap system by lattice defects.