Composition and structure design of three-layered composite phosphors for high color rendering chip-on-board light-emitting diode devices

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 (R_f) of 93, the gamut index (R_g) 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.