Sr/Ba substitution induced higher thermal stability far red-emitting Ba1−ySryLaLiWO6:Mn4+ phosphors for plant growth applications

Abstract

A series of red-emitting BaLaLiWO₆:Mn⁴⁺ (BLLW:Mn⁴⁺) 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 Mn⁴⁺ 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%Mn⁴⁺ at 150 °C was about 22% of the initial value at room temperature. In contrast, the emission intensity of SrLaLiWO₆:1.2%Mn⁴⁺ 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 Mn⁴⁺.