Rare earth doped core-shell particles as phosphor for warm-white light-emitting diodes

Light-emitting diodes (LEDs) are efficient, energy-saving light sources. Unfortunately, designing phosphors for LEDs that emit warm white light is not straightforward. We solvothermally prepared rare earth doped alkaline earth sulfides with a core-shell structure in order to obtain a physical separation between different dopants (europium and cerium). Cathodoluminescence of a single phosphor particle in an electron microscope proves simultaneous Eu2+ and Ce3+ broad band emission. The emission color can be tuned by variation of the composition, core size, and shell thickness. Upon excitation of SrS:Eu2+-SrS:Ce3+ core-shell structures at 430 nm, white light emission with good color rendering and a color temperature around 3000 K is obtained.