Ce3+-Activated γ-Ca2SiO4 and Other Olivine-Type ABXO4 Phosphors for Solid-State Lighting

Yellow-emitting phosphors activated by Ce 3+ are key components of white light-emitting diodes (LEDs) based on the blue (Ga,In)N LED. In these phosphors, the electronic environment around Ce 3+ determines its photoluminescence wavelengths. Placing Ce 3+ in octahedral sites in oxides can potentially lead to yellow or orange phosphors that can compete with the important commercial phosphor, Y 3 Al 5 O 12:Ce. However, there are very few examples of such materials. In this article, we explore the photoluminescent behavior of Ce 3+ in oxides with the olivine structure, whereby two distorted octahedral doping sites exist. We demonstrate that the promising new yellow phosphor γ-Ca 2 SiO 4:Ce requires a second dopant, Al 3+, to avoid the formation of the undesired β polymorph. Our results indicate that the yellow emission is indirectly caused by the complex polymorphism of Ca 2 SiO 4, particularly the low temperature formation of the γ-phase. The dramatic shift in emission from yellow to light-blue when this phosphor is heated to 800 ° C is explained in terms of the redistribution of Ce 3+ in the lattice. A similar effect is observed when Si 4+ is substituted by Ge 4+ . The light-blue emission of Ca 2 GeO 4:Ce,Al is reported as well as the photoluminescent properties of the Ca 2 (Ge,Si)O 4:Ce,Al solid solution.