The luminescence properties of CaZnOS: Bi3+, Sm3+, Li+ phosphors with tunable emissions and energy transfer for white emission

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 ³P_1,0→¹S₀ transition of Bi³⁺, and four red emitting bands within the wavelength range of 550–750 nm which can be assigned to the ⁴G_5/2→⁶H_J (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).