Preparation and Luminescence Properties of Ba₅Si₈O₂₁ Long Persistent Phosphors Doped with Rare-Earth Elements

The phosphors of formula Ba₅Si₈O₂₁:Eu²⁺,Dy³⁺ were synthesized and studied in order to improve their properties. Their synthesis conditions were evaluated as a function of precursors, crucible composition, flux agents, dopants and temperatures. The samples were characterised by means of a systematic investigation through elemental, kinetic, mineralogical (both qualitative and quantitative), and morphological analysis. This study allows for a careful evaluation of the parameters that influence the formation and properties of Ba₅Si₈O₂₁:Eu²⁺,Dy³⁺ phosphors. As for the synthesis conditions, the use of Na₂SiO₃, BaCO₃ and NH₄Cl as precursors was very important to reduce the temperature and time of synthesis. The reducing atmosphere produced with purified coal was cheaper and gave results similar to the more traditional gas mixture (H₂/N₂). At the end of this study, a phosphor with improved long persistent phosphorescence (LPP) characteristics was obtained with Ba/Si = 0.7, Eu/Si = 2.8 × 10^-3 and Dy/Si = 3.6 × 10^-3 following a 6 h-synthesis in a quartz crucible.