Abstract

An innovative spectral conversion scheme for light emitting diodes using fluorescent microspheres has been demonstrated. An optimally mixed proportion of green and red fluorescent microspheres were coated onto a high-extraction-efficiency GaN micro-LED with emission centred at 470 nm. The microspheres self-assemble into ordered hexagonally arrays, forming regular and uniform coating layers. Devices with cool and warm white emission were achieved. The bluish-white LED has a luminous efficacy of 27.3 lm/W (at 20 mA) with CIE coordinates of (0.26, 0.28) and 8500K CCT, while the yellowish-white LED has a luminous efficacy of 26.67 lm/W (at 20 mA) with CIE coordinates of (0.36, 0.43) and 13000K CCT.

© 2008 Optical Society of America

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References

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  1. N. Narendran, N. Maliyagoda, L. Deng, and R. Pysar,"Characterizing LEDs for general illumination applications: mixed-color and phosphor-based white sources," Proc. SPIE 4445, 137-147 (2001).
    [CrossRef]
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    [CrossRef]
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    [CrossRef]
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    [CrossRef]
  7. H. W. Choi and S. J. Chua, "Honeycomb GaN micro-light-emitting diodes," J. Vac. Sci. Tech. B 24, 800-802 (2006).
    [CrossRef]
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    [CrossRef]
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    [CrossRef]
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    [CrossRef]
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    [CrossRef]
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    [CrossRef]
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    [CrossRef]

2007

Y. J. Lee, P. C. Lin, T. C. Lu, H. C. Kuo, and S. C. Wang, "Dichromatic InGaN-based white light emitting diodes by using laser lift-off and wafer-bonding schemes," Appl. Phys. Lett. 90, 161115-161118 (2007).
[CrossRef]

X. Wang, H. Lin, C. M. Li, and S. Tanabe, "Spectral power distribution and quantum yields of a Eu3+-doped heavy metal tellurite glass under the pumping of a violet light emitting diode," Meas. Sci. Technol. 18, 1348-1352 (2007).
[CrossRef]

2006

Y. Xuan, D. C. Pan, N. Zhao, X. L. Ji, and D. G. Ma, Nanotechnology, "White electroluminescence from a poly(N-vinylcarbazole) layer doped with CdSe/CdS core-shell quantum dots," Nanotechnology 17, 4966 (2006).
[CrossRef]

2005

G. Heliotis, P. N. Stavrinou, D. D. C. Bradley, E. Gu, C. Griffin, C. W. Jeon, M. D. Dawson, "Spectral conversion of InGaN ultraviolet microarray light-emitting diodes using fluorene-based red-, green-, blue-, and white-light-emitting polymer overlayer films," Appl. Phys. Lett. 87, 103505-103508 (2005).
[CrossRef]

2002

R. M. Mach, G. O. Mueller, M. R. Krames, and T. Trottier, "High-power phosphor-converted light-emitting diodes based on III-Nitrides," IEEE J. Sel. Top. Quantum Electron. 8, 339-345 (2002).
[CrossRef]

2001

N. Narendran, N. Maliyagoda, L. Deng, and R. Pysar,"Characterizing LEDs for general illumination applications: mixed-color and phosphor-based white sources," Proc. SPIE 4445, 137-147 (2001).
[CrossRef]

1999

J. C. Hulteen, D. A. Treichel, M. T. Smith, M. L. Duval, T. R. Jensen, and R. P. Van Duyne, "Nanosphere Lithography: Size-Tunable Silver Nanoparticle and Surface Cluster Arrays," J. Phys. Chem. B 103, 3854-3863 (1999).
[CrossRef]

1997

J. C. de Mello, H. F. Wittmann, and R. H. Friend, "An improved experimental determination of external photoluminescence quantum efficiency," Adv. Mater. 9, 231 (1997).
[CrossRef]

1995

J. C. Hulteen, and R. P. Van Duyne, "Nanosphere lithography: A materials general fabrication process for periodic particle array surfaces," J. Vac. Sci. Technol. A 13, 1553-1558 (1995).
[CrossRef]

Adv. Mater.

J. C. de Mello, H. F. Wittmann, and R. H. Friend, "An improved experimental determination of external photoluminescence quantum efficiency," Adv. Mater. 9, 231 (1997).
[CrossRef]

Appl. Phys. Lett.

G. Heliotis, P. N. Stavrinou, D. D. C. Bradley, E. Gu, C. Griffin, C. W. Jeon, M. D. Dawson, "Spectral conversion of InGaN ultraviolet microarray light-emitting diodes using fluorene-based red-, green-, blue-, and white-light-emitting polymer overlayer films," Appl. Phys. Lett. 87, 103505-103508 (2005).
[CrossRef]

Y. J. Lee, P. C. Lin, T. C. Lu, H. C. Kuo, and S. C. Wang, "Dichromatic InGaN-based white light emitting diodes by using laser lift-off and wafer-bonding schemes," Appl. Phys. Lett. 90, 161115-161118 (2007).
[CrossRef]

IEEE J. Sel. Top. Quantum Electron.

R. M. Mach, G. O. Mueller, M. R. Krames, and T. Trottier, "High-power phosphor-converted light-emitting diodes based on III-Nitrides," IEEE J. Sel. Top. Quantum Electron. 8, 339-345 (2002).
[CrossRef]

J. Phys. Chem. B

J. C. Hulteen, D. A. Treichel, M. T. Smith, M. L. Duval, T. R. Jensen, and R. P. Van Duyne, "Nanosphere Lithography: Size-Tunable Silver Nanoparticle and Surface Cluster Arrays," J. Phys. Chem. B 103, 3854-3863 (1999).
[CrossRef]

J. Vac. Sci. Technol. A

J. C. Hulteen, and R. P. Van Duyne, "Nanosphere lithography: A materials general fabrication process for periodic particle array surfaces," J. Vac. Sci. Technol. A 13, 1553-1558 (1995).
[CrossRef]

Meas. Sci. Technol.

X. Wang, H. Lin, C. M. Li, and S. Tanabe, "Spectral power distribution and quantum yields of a Eu3+-doped heavy metal tellurite glass under the pumping of a violet light emitting diode," Meas. Sci. Technol. 18, 1348-1352 (2007).
[CrossRef]

Nanotechnology

Y. Xuan, D. C. Pan, N. Zhao, X. L. Ji, and D. G. Ma, Nanotechnology, "White electroluminescence from a poly(N-vinylcarbazole) layer doped with CdSe/CdS core-shell quantum dots," Nanotechnology 17, 4966 (2006).
[CrossRef]

Proc. SPIE

N. Narendran, N. Maliyagoda, L. Deng, and R. Pysar,"Characterizing LEDs for general illumination applications: mixed-color and phosphor-based white sources," Proc. SPIE 4445, 137-147 (2001).
[CrossRef]

Other

G. O. Mueller, R. B. Mueller-Mach, P. J. Schmidt, T. Justel, G. Sorce, United States Patent 6707353 (2004).

G. H. Negley, United States Patent 6967116 (2005).

I. Speier and M. Salsbury, "Color temperature tunable white light LED System," Proc. SPIE 6337, 63371F1-12 (2006).
[CrossRef]

H. W. Choi and S. J. Chua, "Honeycomb GaN micro-light-emitting diodes," J. Vac. Sci. Tech. B 24, 800-802 (2006).
[CrossRef]

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Figures (5)

Fig. 1.
Fig. 1.

Schematic diagram of microsphere-array coated hexLED.

Fig. 2.
Fig. 2.

(a) EL spectrum of the blue LED excitation source. PL spectrum of the (b) green, (c) red and (d) mixture of green and red microspheres.

Fig. 3.
Fig. 3.

SEM images of (a) monolayer and (c) multilayered arrays of microspheres coated on a GaN substrate. The corresponding schematics diagrams are shown in (b) and (c).

Fig. 4.
Fig. 4.

EL spectra (biased at 20 mA) of uncoated (black solid line) and fluorescent microsphere coated LED (coloured lines). The inset shows the magnified spectral region of fluorescence from green and red microspheres

Fig. 5.
Fig. 5.

Emission spectra from the fluorescent microsphere device.

Equations (1)

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Φ E = 400 nm 700 nm P ( λ ) d λ

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