Toward scatter-free phosphors in white phosphor-converted light-emitting diodes

Hoo Keun Park,Ji Hye Oh,Young Rag Do

doi:10.1364/oe.20.010218

Abstract

Scatter-free phosphors promise to suppress the scattering loss of conventional micro-size powder phosphors in white phosphor-converted light-emitting diodes (pc-LEDs). Large micro-size cube phosphors (~100 μm) are newly designed and prepared as scatter-free phosphors, combining the two scatter-free conditions of particles based on Mie’s scattering theory; the grain size or grain boundary was smaller than 50 nm and the particle size was larger than 30 μm. A careful evaluation of the conversion efficiency and packaging efficiency of the large micro-size cube phosphor-based white pc-LED demonstrated that large micro-size cube phosphors are an outstanding potential candidate for scatter-free phosphors in white pc-LEDs. The luminous efficacy and packaging efficiency of the Y3Al5O12:Ce3+ large micro-size cube phosphor-based pc-LEDs were 123.0 lm/W and 0.87 at 4300 K under 300 mA, which are 17% and 34% higher than those of commercial powder phosphor-based white LEDs (104.8 lm/W and 0.65), respectively. In addition, the introduction of large micro-size cube phosphors can reduce the wide variation in optical properties as a function of both the ambient temperature and applied current compared with those of conventional powder phosphor-based white LEDs.

Highlights

White light phosphor-converted light-emitting diodes are obtained via a combination of the transmission of the blue emission through phosphors from blue InGaN LEDs and the broad yellow emission from Y3Al5O12:Ce3+ (YAG:Ce) phosphors because the blue and yellow emissions are complementary colors [1,2,3,4]
The YAG:Ce phosphor-based white phosphor-converted light-emitting diodes (pc-LEDs) comprise a significant portion of the LED white lighting market due to their broad emission spectrum, high absorption strength, excellent thermal quenching, high quantum efficiency, excellent chemical stability, and fast decay time
The development of highly efficient pc-LEDs with scatter-free phosphors has been undertaken by various research groups, significant progress has not yet been made in replacing the commercialized micro-size powder phosphor (MPP) due to the problems encountered during the new scatter-free phosphor implementation

Summary

Introduction

White light phosphor-converted light-emitting diodes (pc-LEDs) are obtained via a combination of the transmission of the blue emission through phosphors from blue InGaN LEDs and the broad yellow emission from Y3Al5O12:Ce3+ (YAG:Ce) phosphors because the blue and yellow emissions are complementary colors [1,2,3,4]. The internal quantum efficiency (IQE) of the YAG:Ce micro-size powder phosphor (MPP) is over 0.9 [5, 6], considerable effort has been made to develop highly efficient YAG:Ce-based white pcLEDs for applications in solid state lighting, because micro-size powder-based pc-LEDs provide limited conversion efficiency (CE) for emission from the powder phosphor layer. This low CE (~0.62 at a YAG:Ce MPP concentration of 25 wt% in paste) is due to the high scattering and reflecting loss of the blue excitation and yellow emission light from the coated micro-size phosphor particles [7, 8]. It is necessary to develop a new morphologically modified YAG:Ce phosphor that can satisfy the requirements for scatter-free phosphors and be implemented in a pcLED package, so that they can replace MPPs in conventional white pc-LEDs

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Conclusion