Synthesis and luminescent properties of spindle-like CaWO4:Sm3+ phosphors

Spindle-like CaWO₄:Sm³⁺ phosphors were prepared via a Polyvinylpyrrolidone (PVP)-assisted sonochemical process, and characterized by using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and photoluminescence spectroscopy (PL). The XRD results suggested that the prepared samples are single-phase. The FE-SEM images indicated that the prepared CaWO₄:Sm³⁺ phosphors are composed of many spindles with maximum average diameter of 150 nm and maximum average length of 500 nm. Under 404 nm excitation, the characteristic emissions corresponding to ⁴G_5/2 → ⁶H_J (J = 5/2, 7/2, 9/2 and 11/2) transitions of Sm³⁺ in CaWO₄ phosphors were observed. The color coordinates for 1 mol% Sm³⁺ doped CaWO₄ phosphor were calculated to be (0.595, 0.404). The fluorescent concentration quenching of Sm³⁺ doped spindle-like phosphors was studied based on the Van Uitert's model, and it was found that the electric dipole–dipole (D–D) interaction is the dominant energy transfer mechanism between Sm³⁺ ions in the CaWO₄:Sm³⁺ phosphors. The critical energy transfer distance was estimated.