Phosphors and White LED Packaging
Both phosphors and the LED packaging play a crucial role in optical properties of white LEDs. The selection criteria of the host lattice, activator ions as well as phosphors utilized in white LEDs are firstly discussed, followed by the overview of the tec
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Phosphors and White LED Packaging Rong-Jun Xie and Naoto Hirosaki
Abstract Both phosphors and the LED packaging play a crucial role in optical properties of white LEDs. The selection criteria of the host lattice, activator ions as well as phosphors utilized in white LEDs are firstly discussed, followed by the overview of the technologically important phosphors, including yttrium aluminum garnets, alkaline earth orthosilicates, alkaline earth sulfides/thiogallets, and (oxo) nitridosilicates (i.e., nitrides). Typically, (oxo)nitridosilicate phosphors are highlighted and introduced in this chapter as they have significantly red-shifted photoluminescence spectra, abundant emission colors and high reliability. Then, the LED packaging configurations, such as “phosphor-in-cup,” “remote-phosphor,” and quantum dot (QD) white LEDs, are discussed in terms of their luminous efficacy, color rendering index, and color temperature. Finally, some issues on phosphors (materials searching, color tuning, particle size, and geometry) and white LEDs (packaging configurations and reliability assessments) are addressed.
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Introduction
Although there are lots of issues needed to be addressed in white LEDs, such as chip processing, light extraction efficiency, heat sink structures, resin materials, reliability, and life test this chapter focuses on phosphors materials and their applications in white LED packaging. White light-emitting diodes are attracting considerable attention from both academic and industrial communities, because they are generally accepted as the next-generation energy saving and green solid-state lighting sources. A world record of 130 lm/W at 1A drive current for white LEDs with the color temperature
R.-J. Xie (✉) ⋅ N. Hirosaki National Institute for Materials Science (NIMS), Tsukuba, Japan e-mail: [email protected] © Springer Nature Singapore Pte Ltd. 2017 T.-Y. Seong et al. (eds.), III-Nitride Based Light Emitting Diodes and Applications, Topics in Applied Physics 133, DOI 10.1007/978-981-10-3755-9_14
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of 4700 K was announced recently by Nichia [1], and Cree also claimed a R&D record of 254 lm/W at a drive current of 350 mA [2]. Nevertheless, such performance levels greatly surpass that of fluorescent tubes (∼80–100 lm/W), and far exceed that of incandescent (∼17 lm/W) and halogen (∼25 lm/W) lamps. Thanks to the great progress in optical qualities (luminous efficacy, color temperature, color rendition, lifetime, etc.), white LEDs are now penetrating into the lighting market very rapidly, which are steadily replacing incandescent lamps and fluorescent tubes for general lighting, cold cathode fluorescent lamps (CCFL) for liquid crystal display TVs for backlighting, or substitute Xeon lamps for automotive headlights. The use of white LEDs will significantly save huge electrical energy, and reduce carbon emissions [3]. For example, the worldwide energy saving would reach ∼1000 TW ⋅ h/year if all traditional lighting sources were replaced by white LEDs. This corresponds to a bu
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