Abstract
A three-layered phosphor structure was designed and prepared by the spin coating of BaSi2N2O2:Eu (cyan-emitting) and (Sr,Ca)AlSiN3:Eu (red-emitting) phosphor films on the yellow-emitting Y3Al5O12:Ce (YAG:Ce) phosphor ceramic synthesized by the solid-state reaction under vacuum sintering. In order to achieve high color rendering lighting, the influence of the composition and structure of the three-layered phosphors on the optical, thermal, and electrical properties of the chip-on-board (COB) packaged white-light-emitting diodes (WLEDs) was studied systematically. The WLED with the structure of “red+cyan+yellow” (R+C+Y) three-layered phosphor generated neutral white light and had a luminous efficacy of 75 lm/W, the fidelity index (Rf) of 93, the gamut index (Rg) of 97, and the correlated color temperature (CCT) of 3852 K. Under the excitation of laser diode (LD), the layer-structured phosphor yielded the white light with a luminous efficacy of 120 lm/W, color rendering index (CRI) of 90, and CCT of 5988 K. The result indicates that the three-layered phosphor structure is a promising candidate to achieve high color rendering and high luminous efficacy lighting.
Highlights
Solid-state lighting devices based on white-light-emittingJ Adv Ceram 2021, 10(4): 729–740 attractive excitation sources to achieve high brightness and high-quality white light if combined with phosphors, because the external quantum efficiency of laser diode (LD) increases linearly as a function of operating current without the problem of “efficiency droop” [2,3].A typical approach to obtain high-power white light is to combine high-brightness blue light-emitting diodes (LEDs) or LDs with appropriate yellow phosphor converters [4,5,6]
The highly efficient Y3Al5O12:Ce (YAG:Ce) ceramic phosphors have been investigated extensively, and they often manifest high efficiency but suffer from low color rendering index (CRI) value, which indicates that the white light produced by using YAG:Ce is not accepted for general lighting
When the Eu ions are doped in (Sr,Ca)AlSiN3, the emission peak which can be attributed to the transition of 4f65d1 → 4f7 is located at 634 nm [37,38,39,40]
Summary
J Adv Ceram 2021, 10(4): 729–740 attractive excitation sources to achieve high brightness and high-quality white light if combined with phosphors, because the external quantum efficiency of LDs increases linearly as a function of operating current without the problem of “efficiency droop” [2,3]. Composite phosphor ceramics consisting of both red- and yellow-emitting phosphors are expected to realize high color rendering lighting. The composite ceramics had severe interfacial chemical interactions because of the composition difference between these two phosphors To overcome this interfacial reaction problem, it would be a good way to coat a red phosphor film on the YAG:Ce ceramic. Many red phosphors with excellent performance have been studied recently [21,22] Among these red phosphors, (Sr,Ca)AlSiN3:Eu is considered as the ideal red-emitting phosphor for high-power LEDs (hp-LEDs) or LDs because it has wide excitation and emission bands, as well as high thermal quenching temperatures [23,24,25]. To realize high color rendering, the red-emitting (Sr,Ca)AlSiN3:Eu and the cyan-emitting BaSi2N2O2:Eu phosphors were chosen, and their films were coated on the YAG:Ce phosphor ceramic. IES TM-30-15 evaluation system, in which the fidelity index (Rf) and the gamut index (Rg) are used to evaluate the color rendering of the light simultaneously, was used in the evaluation of the white LED devices
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