Abstract
β-sialon (Si6-zAlzOzN8-z):Eu oxynitride phosphor is suitable to be used as a green phosphor for the wide-color gamut white LEDs backlighting system, when combined with a blue LED chip and CaAlSiN3:Eu red phosphor, because of its sharp and asymmetric emission spectrum shape.[1, 2] The display color gamut can be widened by the utilization of β-sialon:Eu because its emission spectrum is blue shifted and width of the emission spectrum is narrowed with decreasing z value down to less than 0.1. [3] β-sialon:Eu with low z values of less than 0.1 hereinafter referred to “sharp β-sialon:Eu”. However, the color gamut of the display with sharp β-sialon:Eu and CaAlSiN3:Eu is restricted due to the large full-width at half maximum of the emission spectrum of CaAlSiN3:Eu (> 90 nm).In this work, we attempted to use the K2SiF6:Mn phosphor as an alternative red phosphor which has a sharp emission spectrum, and a sharp β-sialon:Eu as the green phosphor, for the purpose of improving the display color gamut and brightness. White LEDs were fabricated by combining a InGaN blue LED chip peaked at 445nm and sharp β-sialon:Eu (z=0.05) as a green phosphor and K2SiF6:Mn or CaAlSiN3:Eu as a red phosphor. Figure 1 shows emission spectra of fabricated white LEDs and the transmittance spectra of RGB filter are also shown in Fig. 1. Table I shows the color gamut and the brightness of the displays using the white LEDs as the backlight devices. The display using K2SiF6:Mn showed wider NTSC ratios and higher brightness compared to that using CaAlSiN3:Eu. The superiority of the display using K2SiF6:Mn shown in Table I was mainly attributed to the very narrow emission spectrum of the red phosphor. Moreover, the color gamut of the display with the sharp β-sialon:Eu phosphor and K2SiF6:Mn phosphor was mostly able to cover the NTSC triangles as shown in Fig. 2. [1] N. Hirosaki, R-J. Xie, K. Kimoto, T. Sekiguchi, Y. Yamamoto, T. Suehiro, and M. Mitomo, Appl.Phys.Lett. 86, 211905 (2005). [2] R.-J. Xie, N. Hirosaki, and T. Takeda, Appl. Phys. Express. 2, 200401 (2009). [3] K. Takahashi, K. Yoshimura, M. Harada, Y. Tomomura, T. Takeda, R.-J. Xie, and N. Hirosaki, Sci. Adv. Mater. 13, 015004 (2012). Figure 1
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