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Description
Single-component white light phosphors with high thermal stability and balanced photometric properties are essential for next-generation solid-state lighting. In this work, Dy3+-activated SrGd2O4 phosphors were successfully synthesized using a hydrothermal method followed by calcination, and the influence of symmetry-driven site engineering on their structural, optical, and luminescent properties was systematically investigated. X-ray powder diffraction confirmed the formation of a pure orthorhombic SrGd2O4 phase, while peak shifts revealed preferential substitution of Dy3+ ions at Sr2+ sites up to 7 mol%, followed by partial occupation of Gd3+ sites at higher concentrations. Ultraviolet–visible (UV-vis) diffuse reflectance spectra showed strong UV absorption, with a gradual reduction in the band gap from 5.05 to 4.87 eV upon Dy3+ incorporation, suggesting modulation of the electronic structure. Photoluminescence studies revealed characteristic Dy3+ emissions at 480 nm (4F9/2 → 6H15/2), 572 nm (4F9/2 → 6H13/2), and 635 nm (4F9/2 → 6H11/2). The asymmetry-ratio analysis confirmed the dominance of electric dipole transitions and revealed symmetry-dependent site occupancy of Dy3+ ions. Lifetime measurements showed millisecond decay dynamics, with efficient Gd3+ → Dy3+ energy transfer and dipole–dipole–mediated concentration quenching. Among all compositions, the optimized SG-7Dy phosphor exhibited balanced white emission with chromaticity coordinates (0.305, 0.324), close to natural daylight, along with low colour purity (~12%), improved colour rendering index, and high luminous efficacy. Temperature-dependent photoluminescence analysis demonstrated stable white light emission with an activation energy of 0.72 eV, confirming strong resistance to thermal quenching. Thermoluminescence studies revealed Dy3+-mediated trap engineering that optimizes shallow and intermediate trap levels, enhancing persistent luminescence behaviour. Thermal analyses (TGA and DSC) confirmed excellent thermal stability with minimal mass loss and no significant phase transitions. Overall, symmetry-engineered SrGd2O4:Dy3+ phosphors enable efficient single-phase white-light emission with excellent thermal stability, making the optimized SG-7Dy composition a promising candidate for advanced white-light-emitting diode (w-LED) applications.