Enhanced self-activated far-red photoluminescence from Sr₃LiSbO₆ phosphors by Gd³⁺ doping for plant growth

Sr₃LiSbO₆ phosphors were prepared by high temperature solid state reaction method. The crystal phase, morphology and optical properties were characterized by X-ray powder diffraction spectroscopy, scanning electronic microscope, absorption and photoluminescence (PL) spectra. The XRD Rietveld refinement was performed to obtain the detailed crystal structure of Sr₃LiSbO₆. The electronic structure was analyzed by density functional theory (DFT) calculation. Sr₃LiSbO₆ possessed indirect band structure and the band-gap were determined to be 3.17 eV. Self-activated far-red emissions at 630-800 nm were detected under the excitation at 340 nm, which was proposed to originate from the transition between interstitial oxygen defective state to six hybrid 4d¹⁰5s⁰ states of Sb⁵⁺ according to the results of PL spectra of samples annealed at different atmospheres. The PL intensity can be significantly enhanced by 2.9 times after doping 2 mol% Gd³⁺ ions in Sr₃LiSbO₆. The internal quantum efficiency of Sr₃LiSbO₆:2 mol%Gd³⁺ was determined to be 25.2%. The influence of the Gd³⁺ doping on the self-activated PL lifetimes of Sr₃LiSbO₆ and the thermal quenching property of Sr₃LiSbO₆:2 mol%Gd³⁺ was studied.