Jpn. J. Appl. Phys. 45 (2006) pp. L910-L912  |Previous Article| |Next Article|  |Table of Contents|
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Letter

Effects of Phosphor Application Geometry on White Light-Emitting Diodes

Hisashi Masui1,2, Shuji Nakamura1,2 and Steven P. DenBaars1,2

1Materials Department, College of Engineering, University of California, Santa Barbara, CA 93106-5050, U.S.A.
2NICP/ERATO UCSB Group, Japan Science and Technology Agency, University of California, Santa Barbara, CA 93106-5050, U.S.A.

(Received June 14, 2006; accepted July 22, 2006; published online August 25, 2006)

We fabricated white light-emitting diode lamps with three types of commercial yellow-emitting phosphors and studied the effects of phosphor application geometry. Two advantages were confirmed when low-concentration phosphor/silicone mixtures were employed: a 20% increase in output luminous flux and a reduced shift in the chromaticity coordinates upon change in diode current. We propose a simple model to describe these experimental results. According to the model, the results were attributed to reduced phosphor self-absorption (in the yellow spectral range) and reduced absorption saturation (in the blue spectral range), respectively, of the low-concentration mixture. The mathematical expression of the model will be effective for designing white light-emitting diodes based on the phosphor down-conversion technique.

URL: http://jjap.jsap.jp/link?JJAP/45/L910/
DOI: 10.1143/JJAP.45.L910
KEYWORDS:solid-state lighting, light-emitting diode (LED), phosphor down-conversion, absorption saturation, self-absorption


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References | Citing Articles (9)

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  6. E. Rosencher and B. Vinter: Optoelectronics (Cambridge University Press, U.K., 2002) p. 98.
  7. Here we make an estimation. A 10-mW blue-LED die emits 2 ×1016 photons per second. A white LED uses 1 µg of YAG-based phosphor, which contains 1 ×1015 units of Y3Al5O12. If Ce has replaced Y by 6%, 2 ×1014 atoms of Ce exist in 1 µg of phosphor. This means a Ce atom receives a photon every ten milliseconds. This rate will compete with the relaxation rate of the phosphor.
  8. Since the LED lamps were not spherical, differences in the light path length x in different directions became a concern as discussed later in the text. LED lamps with a crude adjustment in the path length were fabricated as well by applying clear silicone partially within a lamp encapsulation. They indicated the same trend in performance as the homogeneously encapsulated LEDs did.

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