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High luminous flux from single crystal phosphor-converted laser-based white lighting system

Michael Cantore, Nathan Pfaff, Robert M. Farrell, James S. Speck, Shuji Nakamura, and Steven P. DenBaars

Open Access Open Access

Abstract

The efficiency droop of light emitting diodes (LEDs) with increasing current density limits the amount of light emitted per wafer area. Since low current densities are required for high efficiency operation, many LED die are needed for high power white light illumination systems. In contrast, the carrier density of laser diodes (LDs) clamps at threshold, so the efficiency of LDs does not droop above threshold and high efficiencies can be achieved at very high current densities. The use of a high power blue GaN-based LD coupled with a single crystal Ce-doped yttrium aluminum garnet (YAG:Ce) sample was investigated for white light illumination applications. Under CW operation, a single phosphor-converted LD (pc-LD) die produced a peak luminous efficacy of 86.7 lm/W at 1.4 A and 4.24 V and a peak luminous flux of 1100 lm at 3.0 A and 4.85 V with a luminous efficacy of 75.6 lm/W. Simulations of a pc-LD confirm that the single crystal YAG:Ce sample did not experience thermal quenching at peak LD operating efficiency. These results show that a single pc-LD die is capable of emitting enough luminous flux for use in a high power white light illumination system.

© 2015 Optical Society of America

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Figures (4)
Fig. 1
Fig. 1 Illustration of the LED epitaxial area and LDepitaxial area needed to produce enough power to replace a 60 W incandescent bulb.

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Fig. 2
Fig. 2 Photograph of the experimental setup showing a 50 cm integrating sphere, a YAG:Ce single crystal phosphor disc at the center of the integrating sphere, and a commercial GaN-based LD located at the side access port of the integrating sphere that was aligned so that it was incident on the phosphor disc. The YAG:Ce single crystal phosphor disc was oriented so that laser beam was incident at an angle 30° from the surface normal of the disc to avoid reflections back to the LD.

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Fig. 3
Fig. 3 (a) Dependence of luminous flux and luminous efficacy of the pc-LD on current. (b) Spectra of the pc-LD at 1.4 and 3 A.

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Fig. 4
Fig. 4 Calculations of luminous efficacy and CCT for a two component pc-LD where the LD wavelength was varied from 400 nm to 470 nm in steps of 5 nm and the spectra of the YAG:Ce phosphor is the same as the spectra that was presented in Fig. 3(b). The calculations assume that the WPE of the LD is 31.6% and that the quantum efficiency of the YAG:Ce phosphor is 95%.

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Tables (1)

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Table 1 Laser diode properties.

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