A strategy to increase phosphor brightness: Application with Ce3+-doped Gd3Sc2Al3O12

Abstract

Y3Al5O12 (YAG) doped with Ce3+ ions is widely used as a phosphor for the generation of white light in LEDs. However, the material presents intrinsic drawbacks: (1) a yellow emission band lacking a red component, leading to a “cold” white light and (2) limited cerium incorporation (~ 3mol%), resulting in poor absorption and thus limiting the external quantum efficiency (EQE) of the LED device. In order to increase phosphor absorption and thus phosphor brightness, we propose here an original strategy based on the increase of Ce content in a phosphor compound, while preserving a high internal luminescence quantum yield. For this purpose, we introduce Ce3+-doped Gd3Sc2Al3O12 (GSAG: Ce). Gd3(1-x)Ce3xSc2Al3O12 polycrystalline samples were prepared through a solid-state microwave-assisted reaction, with x varying from 0 to 0.5; Ce3+ ions can be incorporated into the GSAG matrix with a concentration up to approximately x=0.18 (i.e. 18mol%) without the formation of a parasitic phase. The maximum emission wavelength is located at 573nm for a doping concentration of x=0.1, giving an orange feature to the emission. The internal luminescence quantum yield (Φ) is 52% for Ce concentration up to x=0.03. The EQE, which is proportional to the product of Φ by the Ce concentration when considering a thin transparent phosphor layer is predicted to be about 30% stronger when using GSAG doped with 10mol% Ce (x=0.1), with respect to YAG doped with 2mol% Ce (x=0.02).