Ce3+-Activated γ-Ca2SiO4and Other Olivine-Type ABXO4Phosphorsfor Solid-State Lighting.

Yellow-emitting phosphors activatedby Ce3+are keycomponents of white light-emitting diodes (LEDs) based on the blue(Ga,In)N LED. In these phosphors, the electronic environment aroundCe3+determines its photoluminescence wavelengths. PlacingCe3+in octahedral sites in oxides can potentially leadto yellow or orange phosphors that can compete with the importantcommercial phosphor, Y3Al5O12:Ce.However, there are very few examples of such materials. In this article,we explore the photoluminescent behavior of Ce3+in oxideswith the olivine structure, whereby two distorted octahedral dopingsites exist. We demonstrate that the promising new yellow phosphorγ-Ca2SiO4:Ce requires a second dopant,Al3+, to avoid the formation of the undesired β polymorph.Our results indicate that the yellow emission is indirectly causedby the complex polymorphism of Ca2SiO4, particularlythe low temperature formation of the γ-phase. The dramatic shiftin emission from yellow to light-blue when this phosphor is heatedto 800 °C is explained in terms of the redistributionof Ce3+in the lattice. A similar effect is observed whenSi4+is substituted by Ge4+. The light-blueemission of Ca2GeO4:Ce,Al is reported as wellas the photoluminescent properties of the Ca2(Ge,Si)O4:Ce,Al solid solution. [ABSTRACT FROM AUTHOR]