Regulation of the Crystal Structure and Luminescence Properties of a BaLa_1.6ZnO₅:0.4Eu³⁺ Phosphor by Gd³⁺-Mg²⁺ Codoping for Solar Energy Utilization

Converting solar UV to red/far-red (VTR/FR) light can boost crop photosynthesis and morphogenesis. Consequently, broadband ultraviolet excitation and red/far-red emission phosphors are important VTR/FR light-conversion auxiliaries (LCAs) in solar greenhouses and solar cells. In this study, we have designed and synthesized a series of solid solution BaLa_2-<i>_x-y</i>Gd_<i>y</i>Zn_1-<i>z</i>Mg_<i>z</i>O₅:<i>x</i>Eu³⁺ phosphors. A Gd³⁺-Mg²⁺ cosubstituted La³⁺-Zn²⁺ strategy has been employed to regulate the crystal structure and local crystal field strength of the solid solution. At a low level of Gd³⁺-Mg²⁺ doping, the phosphor exhibited a tetragonal symmetric (BaLa₂ZnO₅) structure and an <i>I</i>4<i>/mcm</i> space group. The Eu³⁺ ⁵D₀ → ⁷F₄ transition generated intense far-red (706 nm) luminescence. At higher doping levels, the crystal structure switched to an orthorhombic low-symmetry (BaGd₂ZnO₅) <i>Pbnm</i> space group and ⁵D₀ → ⁷F₂ transition with a red emission at 627 nm. The optimized tetragonal BaLa_0.8Gd_0.8Zn_0.89Mg_0.11O₅:0.4Eu³⁺ phosphor exhibited effective UVA excitation with a far-red emission (706 nm) and high external/internal quantum efficiency (EQE/IQE = 46.3/88.7%). The optimized orthorhombic BaLa_0.2Gd_1.4Zn_0.3Mg_0.7O₅:0.4Eu³⁺ phosphor exhibited UVB excitation with a red emission (627 nm) and EQE/IQE = 46.4/94.3%. The luminescent film laminated glasses (LFLGs) made with the two phosphors had good VTR/FR performance in sunlight, showing potential in greenhouse and solar cell applications.