New Ce³⁺-activated thiosilicate phosphor for LED lighting-synthesis, luminescence studies, and applications

A new Ce³⁺-activated thiosilicate phosphor, BaLa ₂Si₂S₈:Ce³⁺, was synthesized by using solid-state methods in a fused silica ampule and found to crystallize in the structure type of La₂PbSi₂S₈. The crystal structure has been characterized by synchrotron X-ray diffraction and refined with Rietveld methods. This novel cyan-emitting phosphor can be excited over a broad range from UV to blue light (380-450 nm) and generates a broadband emission peaking at 471 nm with a quantum efficiency of 36%. Nonradiative transitions between Ce³⁺ ions in BaLa₂Si₂S ₈:Ce³⁺ have also been demonstrated to be attributable to dipole-dipole interactions, and the critical distance was calculated to be 17.41 Å. When BaLa₂Si₂S₈:Ce³⁺ phosphor was utilized to incorporate with yellow-emitting (Sr,Ca) ₂SiO₄:Eu²⁺ phosphor and red-emitting CaAlSiN₃:Eu²⁺ phosphor on a 430 nm blue LED chip, a warm white light LED device with color rendering index of ∼96 was obtained. The results indicate that cyan-emitting BaLa₂Si₂S ₈:Ce³⁺ can serve as a potential phosphor for incorporation in fabrication of solid-state lighting. The preparation, spectroscopic characterization, quantum efficiency, decay lifetime, thermal-quenching behavior, and related LED device data are also presented.