Excitation dependent quenching of luminescence in LED phosphors. Issue 4 (5th February 2016)

• Record Type: Journal Article
• 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.
• Is Part Of: Physica status solidi. Volume 10:Issue 4(2016)
• Page Start: 310
• Page End: 314
• Publication Date: 2016-02-05
• Subjects: light‐emitting diodes -- phosphors -- quenching -- europium -- nitrides -- luminescence -- droop -- excited state absorption -- cross relaxation; Solid state physics -- Periodicals; 530.4105
• DOI: 10.1002/pssr.201600006
• Languages: English
• ISSNs: 1862-6254

Abstract

Abstract : 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 Eu 2+ doped materials. This topic is of increasing importance, as high brightness blue LEDs have reached outputs >1 W/mm 2 . 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 Eu 2+ 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) Abstract : 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 Eu 2+ centers.