Sol-Gel-Synthesized Mn⁴⁺-Doped Sr₉Gd₂W₄O₂₄ Red Phosphor: Structural, Optical, and EPR Studies for Deep-Red LEDs and...

Double perovskite materials, such as strontium-gadolinium tetra tungstate (Sr₉Gd₂W₄O₂₄), offer tunable luminescence by adjusting composition and structure, making them ideal for LED and display applications. In this study, Sr₉Gd₂W₄O₂₄ phosphors doped with various concentrations of Mn⁴⁺ ions were synthesized using the sol-gel method and systematically investigated to elucidate their structural, optical, and luminescent properties. The XRD and FTIR confirmed the crystal structure and phase purity, while the DRS studies revealed a suitable band gap for optoelectronic applications. Under the excitation of 343 nm, the phosphors exhibit intense red emission at 681 nm, attributed to ²E_g → ⁴A_2g transition of Mn⁴⁺. The photoluminescence color photometry analysis revealed emission in the red region with a color purity of 96.21%. Crystal field analysis helps to estimate factors such as Racah parameters and nephelauxetic parameters. These parameters suggest that Mn⁴⁺ experience a strong crystal field within the Sr₉Gd₂W₄O₂₄ matrix and a moderate degree of covalency between Mn⁴⁺-O^2- bonds. Electron paramagnetic resonance studies were also performed on the current phosphor to investigate the dopant's coordination in the host. The results suggest potential application in deep-red LEDs for plant growth and advanced ceramics for optoelectronics.