Broadband orange phosphor by energy transfer between Ce3+ and Mn2+ in Ca3Al2Ge3O12 garnet host

Abstract

Ca3Al2Ge3O12 phosphors, singly doped with Ce3+ and co-doped with Mn2+, were synthesized by the solid-state reaction in ammonia atmosphere at 1200 °C using Li2CO3 as a flux. The band gap energy of the host was determined to be 3.7 eV. In these phosphors, Ce3+ ions exclusively occupy the Ca2+ site, while Mn2+ ions occupy both the Ca2+ and Al3+ sites. Under 420 nm excitation, the Ce3+:Ca3Al2Ge3O12 phosphor emits bluish-green light from Ce3+ (470 nm) with a Stokes shift established at 2280 cm−1. The Ce3+/Mn2+:Ca3Al2Ge3O12 phosphor excited at 420 nm emits orange light (580 nm) from Mn2+ in the Ca2+ site due to the Ce3+→Mn2+ energy transfer almost exclusively to this site. Ce3+ emission in the co-doped phosphor is very weak, even for relatively small concentrations (1%) of Mn2+. For Mn2+ concentration of 5% it disappears almost completely. Luminescence quantum yields of these phosphors amount to 24% and 20% in the case of Ce3+:Ca3Al2Ge3O12 and Ce3+/Mn2+:Ca3Al2Ge3O12, respectively. The critical distance for Ce3+ → Mn2+ energy transfer was calculated to be 6.2 Å and the efficiency of the energy transfer was estimated as 88%. These parameters suggest a non-uniform distribution of doped ions and the formation of Ce-Mn clusters.