Conformal phosphor coating using capillary microchannel for controlling color deviation of phosphor-converted white light-emitting diodes. Optics Express, 20, 5092-5098

Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan, 430074, China.
Optics Express (Impact Factor: 3.49). 02/2012; 20(5):5092-8. DOI: 10.1364/OE.20.005092
Source: PubMed


We demonstrated a conformal phosphor coating method for phosphor-converted white light-emitting diodes (LEDs) using capillary microchannel formed by a fixture. The mixture of the phosphor particles and the silicone spontaneously flows in capillary microchannel and was pinned at the edge of the fixture due to the surface tension effect. The present coating method was applied to different packaging types with both the conventional chip and the vertical injection chip. Experimental results show this method can efficiently improve the angular color uniformity (ACU). Compared with those samples packaged by conventional dispensing coating, angular color correlated temperature (CCT) deviation of the test samples by the present method can reduce from 1500K to 200K for the average CCT 5200K from -90° to +90 view angles, and reduce from 5000K to 1000K for the average CCT 9150K. Additionally, this method can prevent the packaging non-consistency that the average CCT varies from package to package due to the deviation of phosphor-silicone mixture volume. In the experiments, even when the phosphor-silicone mixture volume varies from 0.3 µl to 0.5 µl, the deviation of the average CCT is less than 80K.

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Available from: Xiaobing Luo, Oct 01, 2014
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    • "In order to enhance ACU, conformal phosphor coating by which phosphor layer is uniformly distributed around the chip was proposed. Many methods, such as settling, spin coating, self-exposure, electrophoretic deposition, and pulsed spray have been applied for conformal coating [8]–[10]. However, these methods have some limits. "
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    ABSTRACT: Conformal phosphor distribution is a well known way to improve optical performance for white light emitting diode (LED) packaging. However, it is difficult to be realized by mature and cheap dispensing coating methods. In this paper, with consideration given to the effect of boundary constraint on liquid wetting morphology, a method to achieve phosphor conformal distribution is presented by conventional dispensing coating with controlling the slanting angle of reflector cups. The numerical simulations and experiments on phosphor dispensed into reflector cups with different slanting angles are conducted. The results show that uniform phosphor distribution can be obtained when the slanting angle is the same as the contact angle between the phosphor slurry and the reflector cup side wall. The rule can be used to guide the design of the reflector cup and a simple change of reflector cup can realize phosphor conformal coating for white LEDs by the low cost traditional dispensing coating process.
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    ABSTRACT: A given corelated color temperature (CCT) for phosphor converted light emitting diodes (pcLED) can be achieved by different phosphor gel concentrations or volumes. Though the CCT is the same, other optic performances may be distinguishable. In this paper, the variety of lumen efficiency and angular color unity (ACU) for LED with given CCT were investigated by Monte Carlo ray-tracing simulations. It is found that though the CCT is the same, the lumen efficiency and the ACU change distinctly with different phosphor gel concentration and volume. For the CCT of 4200 K, 4700 K, and 6000 K, the lumen efficiencies have a variety of 4.1%, 5.9%, and 4.0%, respectively, while the ACUs have a change of 7.4%, 20.1%, and 30.5%, respectively. It is also found that lumen efficiency increases with the increment of the volume of phosphor gel for the same CCT.
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    ABSTRACT: In this study, a method based on the definition of illuminance was presented to design freeform lens for uniform illumination in direct-lit light emitting diode (LED) backlight with high distance-height ratio (DHR). The principle and algorithms of the design method were introduced and several design examples were presented and discussed. Compared with traditional hemispherical lens, the freeform lens designed by the present method can improve the illuminance uniformity greatly, especially when the DHR is large. Monte Carlo simulations show that when the DHR is 3, the uniformity of lighting performance of the optimized freeform lens could be improved as high as 0.8788 while that of the traditional hemispherical lens is only 0.1417.
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