Tailoring red and deep-red light: Bi3+ doped Sr2Gd0.2Eu0.8F7 phosphors for next-generation horticultural LEDs

• Synthesis of Bi 3+ -codoped Sr 2 GdEuF 7 nanophosphors in powder form • Efficient red-light output with untypically strong 5 D 0 → 7 F 4 emission at ∼ 700 nm. • 250 % of PL enhancement is obtained for the optimized sample codoped with 1 % of Bi 3+. • T-dependent PL measurements demonstrate high stability of emission up to 200 °C. • LED device fabricated from a nanophosphor with 1 % Bi 3+ on a 395 nm chip. Eu 3+ -activated inorganic phosphors are widely used in general lighting and display technologies due to their strong orange/red ( 5 D 0 → 7 F 1,2 ) emissions with wavelengths shorter than 630 nm. However, phosphors activated by Eu 3+ that strongly emit in the deep-red region, driven by the 5 D 0 → 7 F 4 transition (>700 nm), are relatively uncommon. This limitation hinders their applicability in horticultural light emitting diodes, where light in the photosynthetically active radiation range, particularly deep-red photons, is crucial for regulating plant growth. Hereby, we prepared Bi 3+ -doped Sr 2 Gd 0.2 Eu 0.8 F 7 nanoparticles using the hydrothermal synthesis method, to address this challenge. Introducing Bi 3+ significantly enhanced Eu 3+ emission under near-UV excitation, with an optimal 1 mol% Bi 3+ concentration yielding a 250 % increase in integrated emission intensity and a long emission lifetime of 9.3 ms compared to the Bi 3+ -free sample. The optimized phosphor also demonstrated exceptional thermal stability, retaining 93 % of its room-temperature emission at 200 °C. These results highlight that Bi 3+ -doping of Sr 2 Gd 0.2 Eu 0.8 F 7 host is a promising strategy for designing thermally robust, deep-red-emitting nanophosphors. Such properties underline their potential for next-generation horticultural LED applications aimed at improving plant growth efficiency.