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Efficient and stable laser-driven white lighting
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Image of FIG. 1.

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FIG. 1.

Excitation and emission spectra, collected at the relative maxima of (a) the blue-emitting phosphor (λ = 335 nm; λ = 452 nm), (b) the green-emitting phosphor (λ = 395 nm; λ = 530 nm), (c) the red-emitting phosphor (λ = 395 nm; λ = 630 nm). (d) shows the relative emission intensities collected at 402 nm excitation.

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FIG. 2.

Schematic illustrations of the experimental setup used to measure laser excited phosphor samples in an integrating sphere. The phosphor encapsulated silicone disk, mounted on a transparent quartz substrate, is positioned with the surface at a slight angle to the incoming laser beam. The resulting device operates in reflection mode due to the dense phosphor pellet, illustrated for (a) the near-UV excited RGB phosphors and (b) the blue excited YAG:Ce.

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FIG. 3.

SPD for phosphor samples (a) RGB and (b) RGB excited using a near-UV (λ = 402 nm) laser diode and (c) the corresponding CIE chromaticity coordinates show white light with a variety of color temperatures is attainable. Photographs of the RGB phosphor sample (d) without and (e) with laser excitation.

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FIG. 4.

(a) Calculated SPD for target white light composed of YAG:Ce and a blue laser diode, (b) experimentally measured SPD with a similar ratio of laser to phosphor emission as that of the calculated SPD, (c) the corresponding CIE chromaticity coordinates, and a photograph of the YAG:Ce phosphor sample (d) without and (e) with laser excitation. The SPDs show the fits to three Gaussian curves, representing the fraction of emitted white light from laser emission and phosphor emission.


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Table I.

Measured properties including the correlated color temperature (CCT), color rendering ( ), luminous flux (ϕ), and luminous efficacy (η) of the resulting white light using the near-UV (λ = 402 nm) laser diode in combination with phosphor samples RGB and RGB and using the blue (λ = 442 nm) laser diode in combination with YAG:Ce.


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Laser-based white lighting offers a viable option as an efficient and color-stable high-power solid-state white light source. We show that white light generation is possible using blue or near-UV laser diodes in combination with yellow-emitting cerium-substituted yttrium aluminum garnet (YAG:Ce) or a mixture of red-, green-, and blue-emitting phosphors. A variety of correlated color temperatures (CCT) are achieved, ranging from cool white light with a CCT of 4400 K using a blue laser diode to a warm white light with a CCT of 2700 K using a near-UV laser diode, with respective color rendering indices of 57 and 95. The luminous flux of these devices are measured to be 252 lm and 53 lm with luminous efficacies of 76 lm/W and 19 lm/W, respectively. An estimation of the maximum efficacy of a device comprising a blue laser diode in combination with YAG:Ce is calculated and the results are used to optimize the device.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Efficient and stable laser-driven white lighting