Structurally stable Mn4+-doped oxide phosphor with improved thermal stability for agricultural lighting

Abstract

Structural and thermal stability are two essential conditions in phosphor research, which are related to the structure of the host and the position of 4T2 energy lever in Mn4+-activated phosphors. Here, Mn4+-activated CaGdAlO4 phosphor with superior structural stability was synthesized through systematically screening the aluminate family of ABAlO4 (A = Mg, Ca, Sr, Ba; BSc, Lu, Y, Gd, La). Sr2+ was subsequently introduced to modulate the 4T2 state level of Mn4+ for achieving better thermal stability in CaGdAlO4:Sr2+,Mn4+ phosphor. The luminescence quenching temperature T1/2 show a parabolic trend with the increasing of Sr2+ dopant in Ca1-yGdAlO4:ySr2+, Mn4+ phosphors, and change from 403 K to 426 K and 387 K in CaGdAlO4:Mn4+, Ca0.4GdAlO4:0.6Sr2+,Mn4+ and SrGdAlO4:Mn4+ three samples, respectively. The corresponding crystal-field calculations confirm that a certain amount of Sr2+ doping can improve the 4T2 state of Mn4+ and obtain better thermal stability in the phosphor. All the samples have deep-red emission located at 712 nm, which matches well with the absorption spectra of green vegetables. This deep-red light accelerate morphological formation and increase vegetable biomass. This work is expected to stimulate more exploration of Mn4+-doped oxide phosphors with better structural and thermal stability for emerging applications of agricultural lighting.