| dc.description.abstract | Recently, white LEDs based on phosphor conversion have accounted for a considerable proportion of the LED market. To meet the requirements of sustainable development, continual enhancement of LED luminous efficiency is crucial. A remote phosphor package is an efficient method for enhancing luminous efficiency. In this study, the light extraction efficiency of a remote phosphor white LED was enhanced using a hemiellipsoidal antireflection subwavelength structure PET film, which was fabricated to reduce the Fresnel reflection of the LED package surface. The completed antireflection subwavelength structure PET film was integrated on the remote phosphor LED surface through a UV-curing adhesive process. The measured results show that the luminous efficiency was enhanced by approximately 11.76% when the ASS film was used. Moreover, the optical properties of color coordinates, color temperature, and color rendering of remote phosphor LEDs were within the measurement error of the measuring equipment when the ASS film was present.
However, in typical remote phosphor white LEDs, the phosphor-scattered blue light and phosphor-emitted yellow light have different radiant intensity distributions. Therefore, the angular color distribution becomes non-uniform, and a yellow ring phenomenon appears in the illuminating plane.The utility of low-cost and controllable TiO2 diffuser-loaded encapsulation provided an effective method for improving the angular color uniformity of remote phosphor white LEDs. An inert TiO2 diffuser content of 0.2 wt.% and a phosphor content of 16.0 wt.% in the phosphor layer were determined to be the optimum conditions for obtaining low angular CCT variance, high luminous efficiency, and maintaining the CCT of white LEDs, simultaneously. We found that the angular color uniformity could be improved by 31.82% in the TiO2 diffuser-loaded encapsulation remote phosphor LED, compared with the non-diffuser remote phosphor LED. At a driving current of 350 mA, the luminous flux of the TiO2 diffuser-loaded encapsulation remote phosphor LED was increased by 8.65% relative to the non-diffuser remote phosphor LED. Finally, we showed that incorporating the TiO2 diffuser into the phosphor layer of the remote phosphor white LED did not influence the reliability of the LED.
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