Excitation dependent quenching of luminescence in LED phosphors

Droop, the decrease of efficiency with increased power density, became a major topic with InGaN LEDs, after its introduction in 2007. This paper provides insight into droop in localized center luminescence phosphors, exemplified here by Eu2+ doped materials. This topic is of increasing importance, a...

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Published in:Physica status solidi. PSS-RRL. Rapid research letters 2016-04, Vol.10 (4), p.310-314
Main Authors: Shchekin, Oleg B., Schmidt, Peter J., Jin, Fahong, Lawrence, Nate, Vampola, Kenneth J., Bechtel, Helmut, Chamberlin, Danielle R., Mueller‐Mach, Regina, Mueller, Gerd O.
Format: Article
Language:English
Subjects:
Absorption
Color
cross relaxation
droop
europium
Excitation
excited state absorption
Indium gallium nitrides
Light emitting diodes
Luminescence
Materials science
nitrides
Phosphors
Quenching
Reduction
Solid state physics
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Summary:Droop, the decrease of efficiency with increased power density, became a major topic with InGaN LEDs, after its introduction in 2007. This paper provides insight into droop in localized center luminescence phosphors, exemplified here by Eu2+ doped materials. This topic is of increasing importance, as high brightness blue LEDs have reached outputs >1 W/mm2. The nonlinearities in phosphor quantum efficiency result in drive‐dependent color point shift and reduction of overall efficiency of phosphor converted white LEDs which utilize Eu2+ activated phosphors. The efficiency quenching can be traced back to two processes, well‐known in laser physics, excited state absorption or/and cross relaxation by Foerster/Dexter transfer. Both processes lead to reduction in phosphor efficiency, but they can be differentiated. Understanding the root cause of efficiency quenching opens ways to minimize the practical consequences. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) Red phosphors used to improve color quality of white LEDs are investigated as the excitation levels are increased. These phosphors show droop, a decrease of efficiency with drive, which is of practical importance and interesting as to its origin. This Letter addresses the reason and claims a responsible loss process, second order in the concentration of excited centers, most likely an excited state absorption (ESA) of the Eu2+ centers.
ISSN:1862-6254
1862-6270
DOI:10.1002/pssr.201600006