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

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 2Eg → 4A2g 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+-O2- 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.