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Understanding the Interactions between Vibrational Modes and Excited State Relaxation in Y3–xCexAl5O12: Design Principles for Phosphors Based on 5d–4f Transitions
journal contribution
posted on 2018-01-29, 23:50 authored by Yuan-Chih Lin, Paul Erhart, Marco Bettinelli, Nathan C. George, Stewart F. Parker, Maths KarlssonThe oxide garnet Y3Al5O12 (YAG),
when a few percent of the activator ions Ce3+ substitutes
for Y3+, is a luminescent material widely used in phosphor-converted
white lighting. However, fundamental questions surrounding the defect
chemistry and luminescent performance of this material remain, especially
in regard to the nature and role of vibrational dynamics. Here, we
provide a complete phonon assignment of YAG and establish the general
spectral trends upon variation of the Ce3+ dopant concentration
and temperature, which are shown to correlate with the macroscopic
luminescence properties of Y3–xCexAl5O12. Increasing
the Ce3+ concentration and/or temperature leads to a red-shift
of the emitted light, as a result of increased crystal-field splitting
due to a larger tetragonal distortion of the CeO8 moieties.
Decreasing the Ce3+ concentration or cosubstitution of
smaller and/or lighter atoms on the Y sites creates the potential
to suppress thermal quenching of luminescence because the frequencies
of phonon modes important for nonradiative relaxation mechanisms are
upward-shifted and hence less readily activated. It follows that design
principles for finding new Ce3+-doped oxide phosphors emitting
at longer wavelengths require tetragonally distorted environments
around the CeO8 moieties and a sufficiently rigid host
structure and/or low activator-ion concentration to avoid thermal
quenching of luminescence.
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Keywords
phonon modesvibrational dynamicsExcited State RelaxationCeO 8 moietiesVibrational Modeshost structureactivator-ion concentrationmacroscopic luminescence propertiescrystal-field splittingY sitesdesign principlesYAGdefect chemistryoxide garnet Y 3 Al 5 O 12phonon assignmentoxide phosphorsDesign Principlesnonradiative relaxation mechanisms
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