Chemical Unit Cosubstitution and Excess Cation Substitution as a Design Strategy for Synergetically Enhancing the Luminescence Performance of Znga2o4 : Cr3+ Phosphors Used for Plant Growth Leds

Cationic substitution is a common material modification strategy. Generally, it follows the principles of radius matching, valency equilibrium and stoichiometric substitution. However, radius-mismatched, nonstoichiometric-ratio ion substitution can achieve unexpected experimental results. Such unexpected results are very important for expanding the research of materials, but the modification mechanism is still unclear. In this work, the optical performance of ZnGa2O4:0.02Cr3+ (ZGO:0.02Cr3+) is effectively regulated by chemical unit cosubstitution (Ge4+-Li+/Na+ for Ga3+-Zn2+) and excess cation substitution synergetic strategies. Ge4+-Li+ and Ge4+-Na+ replace the lattice position of Ga3+-Zn2+ to enhance the photoluminescence (PL) intensity and quantum efficiency (QE) of ZGO:0.02Cr3+. The optimal doping contents of Ge4+-Li+ and Ge4+-Na+ are all 0.3 mol (PL intensity reaches 130.3% and 153.4%, QE=77.4% and 85.1%). With further addition of Li+ ions, the emission intensity and QE continued to increase to 176.4% and 83.8%, respectively. The mechanism of the synergistic effect on optical properties is explained via Rietveld refinement, band gap energy and thermoluminescence. Finally, LED devices were fabricated by using ZGO:0.02Cr3+, 0.03Ge4+, 0.11Li+ phosphor to indicate the effect on plant growth. The growth period was reduced and the fruit quality was improved in dwarf potted tomato, which shows the application prospect in plant growth of ZGO: 0.02Cr3+ phosphor