Sr/Ba substitution induced higher thermal stability far red-emitting Ba 1- y Sr y LaLiWO 6 :Mn 4+ phosphors for plant growth applications.

A series of red-emitting BaLaLiWO 6 :Mn 4+ (BLLW:Mn 4+ ) phosphors were successfully synthesized by a high-temperature solid-state reaction method. The crystal structure and luminescence properties of the obtained samples were systematically investigated. The emission spectra exhibited a deep red emission band peaking at 716 nm with a full width at half-maximum (FWHM) of 44 nm under 340 nm excitation. The optimal Mn 4+ molar concentration was about 1.2%. In addition, the luminescence mechanism was analyzed using a Tanabe Sugano energy level diagram. With the substitution of Sr for Ba, there was a red shift in the emission spectrum and a blue shift in the excitation spectrum. The emission intensity of BLLW:1.2%Mn 4+ at 150 °C was about 22% of the initial value at room temperature. In contrast, the emission intensity of SrLaLiWO 6 :1.2%Mn 4+ still maintained 79% of the initial emission intensity at room temperature at 150 °C. This was due to the fact that with the substitution of Sr for Ba, the W-O bond length gradually decreases, which gradually enhanced the crystal field strength of Mn 4+ .