Article pubs.acs.org/JPCC
High-Quality White Light Using Core−Shell RE3+:LaPO4 (RE = Eu, Tb, Dy, Ce) Phosphors James A. Dorman,† Ju H. Choi,† Gregory Kuzmanich,‡ and Jane P. Chang*,† †
Department of Chemical and Biomolecular Engineering, UCLA, Los Angeles, California 90095, United States Department of Chemistry and Biochemistry, UCLA, Los Angeles, California 90095, United States
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ABSTRACT: Rare-earth (RE = Eu, Dy, Tb, and Ce) ion doped core and core−shell LaPO4 phosphors were synthesized to elucidate the effect of spatial distribution of dopants on the emission spectra. The core−shell architecture was designed as a single particle that can be excited by a single wavelength and yield a balanced white light appearance with long emission lifetimes. Specifically, a multishell architecture was employed to separate the Eu3+ and Tb3+ within the phosphor to circumvent the energy transfer between them, passivate the surface quenching sites, and control Ce3+ doping to sensitize other RE ions. To assess the effectiveness of these core−shell phosphors, the International Commission on Illumination (CIE) coordinates and luminescence lifetimes are quantified as the figures of merit. The Eu3+:LaPO4|Ce3+,Dy3+:LaPO4| Tb3+:LaPO4 layering resulted in CIE coordinates of (0.34, 0.35) using 365 nm excitation, nearly at center of the white light regime at (0.35, 0.35). Finally, the emission lifetimes were measured to be 0.85, 4.34, and 3.26 ms and resulted in a total increase of 31, 36, and 16% over the RE3+:LaPO4 reference phosphors, where RE = Dy, Tb, and Eu, respectively. The synthesized phosphor material has high-quality white light with improved emission lifetimes, suitable for application in white light LED devices.
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INTRODUCTION Since the introduction of solid-state lighting, there has been a push to create high-efficiency, high-quality white light using light-emitting diodes (LEDs).1,2 Solid-state LEDs are promising due to emission efficiencies as high as 95%, much greater than that of incandescent (5%) and fluorescent light sources (∼20%).3 Unfortunately, the light emitted from the LEDs is only a few nanometers wide, requiring additional materials, typically inorganic phosphors, to expand the emission spectrum.4 Many phosphors are doped with rare earth (RE) ions due to the highly stable f−f energy level transitions and a broad range of emission wavelengths.5 To achieve high-quality, high-efficiency white light, these dopants are incorporated into complex inorganic hosts that are difficult and/or expensive to produce.6−8 Typically, the individual RE-doped phosphors are blended at specific ratios, as opposed to using multi-RE ion doped phosphors, when applied to an LED for light conversion. The current state-of-the-art white light LED phosphors are Ce3+,Tb3+:Ca4Y6(SiO4)6O or Mn2+,Cr3+:MgAl2O4, which partially converts UV or blue light (
