title: Cymbal-shaped phosphor structure for phosphor-converted white LEDs.
abstract: High efficiency phosphor-converted white light-emitting diodes with superior color uniformity have been investigated. It is proposed that the cymbal-shaped phosphor structure can improve the uniformity of the angle-dependent correlated color temperature (CCT) and also increase the luminous intensity compared to the conventional dispensing phosphor structure. In this experiment, we form the cymbal-shaped structure, which features a bump upon the central surface of the bottom layer, by employing an injection process after the dispensing coating. The upper bump phosphor layer not only enhances the extraction efficiency of lights, but also compensates the difference of the excitation optical path in the dispensing bottom layer between the normal-concentrated forward-scattered blue rays and those emitted with larger angles. This considerably eliminates the "blue center" phenomenon. The CCT deviation have been reduced from 315 K to 120 K using the cymbal-shaped phosphor coating method, and the light extraction efficiency (LEE) is enhanced by 8.5% compared with conventional dispensing phosphor-converted white LEDs. This new cymbal-shaped design was verified both experimentally and theoretically.
authors.forename: Haibo
authors.initials: H
authors.lastname: Rao
authors.forename: Caineng
authors.initials: C
authors.lastname: Li
authors.forename: Qi
authors.initials: Q
authors.lastname: Zhang
authors.forename: Chunyu
authors.initials: C
authors.lastname: Zhou
authors.forename: Wei
authors.initials: W
authors.lastname: Zhang
authors.forename: Kun
authors.initials: K
authors.lastname: Zhang
authors.forename: Da
authors.initials: D
authors.lastname: Zhou
authors.forename: Qiaolin
authors.initials: Q
authors.lastname: Lei
authors.forename: Xuemei
authors.initials: X
authors.lastname: Wang