Comparative study of the luminescence of Bi doped LaOCl and LaOBr phosphor powders

In this work, Bi3+ doped lanthanum oxyhalides (LaOX, X = Cl or Br) were prepared via the solid-state reaction method in order to compare their photoluminescence (PL) properties and stability. Their structure and morphology were assessed using X-ray diffraction and scanning electron microscopy, while the annealing temperature and doping concentration were optimized for maximum PL emission intensity. The 3P1 → 1S0 emission transitions of Bi3+ ions in LaOCl:Bi and LaOBr:Bi were located in the ultraviolet at 344 nm and 358 nm, for excitation at 266 nm and 273 nm, respectively. The red-shift and lower intensity emission of LaOBr:Bi compared to LaOCl:Bi was attributed to the stronger nephelauxetic effect in the bromide host. Although LaOCl:Bi was not completely stable when stored exposed to the atmosphere for several months, LaOBr:Bi was significantly less stable and also showed accelerated degradation when exposed to a 254 nm UV lamp. Although previous reports for scintillators and upconversion phosphors based on these hosts have found LaOBr to be preferable, direct comparison of PL for these materials doped with Bi3+ ions showed that the LaOCl host was superior.