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Highly-efficient, tunable green, phosphor-converted LEDs using a long-pass dichroic filter and a series of orthosilicate phosphors for tri-color white LEDs

Ji Hye Oh, Jeong Rok Oh, Hoo Keun Park, Yeon-Goog Sung, and Young Rag Do

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Abstract

This study introduces a long-pass dichroic filter (LPDF) on top of a phosphor-converted LED (pc-LED) packing associated with each corresponding tunable orthosilicate ((Ba,Sr)2SiO4:Eu) phosphor in order to fabricate tunable green pc-LEDs. These LPDF-capped green pc-LEDs provide luminous efficacies between 143–173 lm/W at 60 mA in a wavelength range between 515 and 560 nm. These tunable green pc-LEDs can replace green semiconductor-type III-V LEDs, which present challenges with respect to generating high luminous efficacy. We also introduce the highly-efficient tunable green pc-LEDs into tri-color white LED systems that combine an InGaN blue LED and green/red full down-converted pc-LEDs. The effect of peak wavelength in the tunable green pc-LEDs on the optical properties of a tri-color package white LED is analyzed to determine the proper wavelength of green color for tri-color white LEDs. The tri-color white LED provides excellent luminous efficacy (81.5–109 lm/W) and a good color rendering index (64–87) at 6500 K of correlated color temperature (CCT) with the peak wavelength of green pc-LEDs. The luminous efficacy of the LPDF-capped green monochromatic pc-LED and tri-color package with tunable green pc-LEDs can be increased by improving the external quantum efficiency of blue LEDs and the conversion efficiency of green pc-LEDs.

©2011 Optical Society of America

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Figures (9)
Fig. 1
Fig. 1 Schematic diagrams of four different types of full down-converted green LEDs using color conversion materials. Different green pc-LEDs are fabricated using: (a) blue or n-UV/violet LED and a high concentration of phosphors, (b) blue LED and densely sintered translucent ceramic phosphors, (c) blue LED and a CdMgZnSe multiple quantum well structures, (d) blue LED and phosphors capped with a long-pass dichroic filter (LPDF).

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Fig. 2
Fig. 2 (a) The relative luminous efficacies and (b) color purity of green pc-LEDs with and without a LPDF as a function of the phosphor concentration using G550 green phosphor in paste. (c) The luminous efficacy of selected green pc-LEDs with and without a LPDF with similar 1931 CIE color coordinates to the corresponding phosphor as a function of the peak wavelength of a tunable green pc-LED. All measurements were performed under equal-current conditions (60 mA).

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Fig. 3
Fig. 3 (a) Photoluminescence spectra and (b) Color coordinates of a series of orthosilicate green phosphors excited by blue light. (c) Electroluminescence spectra and (d) color coordinates of six different LPDF-capped green pc-LEDs associated with corresponding green phosphors.

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Fig. 4
Fig. 4 (a) Luminous efficacy, (b) Luminous flux, and (c) Color coordinates of conventional InGaN green LED and six tunable LPDF-capped green pc-LEDs as functions of applied current (arrow indicates the increase of current). (d) Luminous efficacy, (e) Luminous flux, and (f) Color coordinates of conventional InGaN green LED and six tunable LPDF-capped green pc-LEDs as functions of ambient temperature (arrow indicates the increase of temperature).

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Fig. 5
Fig. 5 (a) The measured luminous efficacy at 60 mA and the luminous efficiency of the radiation (LER) of six tunable green pc-LEDs. (b) EQE values for a blue (B0.49), a green III-V LED and a family of tunable green pc-LEDs.

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Fig. 6
Fig. 6 The color purity and emission spectra of each green pc-LED with a LPDF as a function of the viewing angle: (a) G515, (b) G521, (c) G530, (d) G540, (e) G550, (f) G560.

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Fig. 7
Fig. 7 (a) Normalized EL emission spectra and (b) Commission Internationale d’Eclairage (CIE) color coordinates of a blue LED, (Sr,Ca)AlSiN3:Eu red pc-LED, and six tunable (Ba,Sr)2SiO4:Eu) green pc-LEDs.

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Fig. 8
Fig. 8 The overlapped integrated emission spectra of each LED in a RB,MGB,MB three-package white-light along with the peak wavelength of the tunable green pc-LEDs at (a) 6500 and (b) 3500 K. The fractional applied current of the primary LEDs in each RB,MGB,MB three-package white light along with the peak wavelength of the tunable green pc-LEDs at (c) 6500 and (d) 3500 K..

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Fig. 9
Fig. 9 (a) Luminous efficacy and (b) color rendering index of RB,MGB,MB three-package white-light at 6500 and 3500 K as a function of the peak wavelength of a tunable green pc-LED.

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Equations (1)

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η e−pc = η lm−m /LER= η e × η con = η e ×( η p × η pkg )
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