Abstract
A series of CaZnOS: Bi3+, Sm3+, Li+ phosphors are prepared by solid-state reaction method at high temperature in H2/N2 atmosphere. The site occupation of activators and luminescence properties, as well as energy transfer mechanism were investigated in detail. The Ca2+ positions are occupied by the Bi3+ and Sm3+ ions according to the XRD Rietveld refinement. Under the excitation at 366 nm, the CaZnOS: Bi3+, Sm3+, Li+ phosphors show an intense broad emitting band peaking at 490 nm owing to the 3P1,0→1S0 transition of Bi3+, and four red emitting bands within the wavelength range of 550–750 nm which can be assigned to the 4G5/2→6HJ (J = 5/2, 7/2, 9/2 and 11/2) transition of Sm3+. The emission color changes from blue-green to orange-red, and the decay time drastically decreased with increasing Sm3+ concentration, attributing to the energy transfer from Bi3+ to Sm3+. In addition, the co-doped phosphor exhibits better thermal quenching property compared with single activated samples. A cold-white LED was fabricated by using single CaZnOS: Bi3+, Sm3+, Li+ as the wavelength conversion phosphor combined with a UV LED chip, and the obtained LED exhibits the high Ra (88.9) and CCT (8836 K).
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