Unlocking novel halogen germanate phosphors for full-spectrum lighting and ultra-sensitive temperature sensing

Exploring multiple emission bands from single rare-earth doped phosphors and developing design principles to enhance brightness and temperature sensing capabilities are key challenges in advanced optical applications and research. Herein, we report a novel Sr₆Ge₂O₇Cl₆:Eu²⁺ (SGOC:Eu²⁺) phosphor and that exhibits three emission bands at 400, 501, and 670 nm. These bands are resolved into four Gaussian peaks, attributed to 5d-4f transitions of Eu²⁺ ions occupying four distinct Sr²⁺ sites. Resolved into four Gaussian peaks, attributed to 5d-4f transitions of Eu²⁺ occupying four distinct Sr²⁺ sites. Energy levels were quantified via Van Uitert equation and lattice distortion analysis. The unique thermal quenching disparity between high-energy (400 nm) and low-energy (501 nm) emissions enables superior temperature sensing, achieving absolute and relative sensitivities of 3.07 % K^-1 (298 K) and 15.22 % K^-1 (498 K), respectively, via fluorescence intensity ratio (I₄₀₀/I₅₀₁). Ge/Si substitution enhances Eu²⁺ incorporation, elevating luminescence intensity by 282 % and quantum efficiency from 23.6 % to 57.5 %, attributed to suppressed non-radiative losses and modified local lattice symmetry. A white LED fabricated with SGOC:Eu²⁺ exhibits exceptional color rendering (Ra = 96). This work highlights the critical role of multi-site engineering in designing high-performance phosphors for ultra-sensitive optical thermometry and efficient solid-state lighting, providing a blueprint for next-generation photonic materials.