Thermally stable Ca2YAl3Ge2O12: Eu3+ deep-red emitting phosphors with anomalous intense 5D0→7F4 transition for plant growth LEDs

Developing high-efficiency and thermally stable deep-red-emitting phosphors is crucial for advancing agricultural illumination. Eu 3+ -activated phosphors hold significant potential in plant growth light-emitting diodes (LEDs). However, achieving highly efficient deep-red emission of Eu 3+ remains challenging owing to the weak 5 D 0 → 7 F 4 transition and thermal quenching. In this study, novel Ca 2 YAl 3 Ge 2 O 12 : Eu 3+ phosphors were successfully synthesized via high-temperature solid-state reaction. Under the excitation of 394 nm, the phosphors exhibited deep-red emission in the wavelength range of 550–750 nm. Notably, the strongest anomalous emission peak was found at 708 nm, corresponding to the 5 D 0 → 7 F 4 transition of Eu 3+ ions, which can be explained using structural analysis. Additionally, the phosphors showed good thermal stability, and its emission intensity at 423 K maintained about 84 % of that at 298 K. The internal quantum efficiency reached 67 %. Furthermore, a prototype LED device was fabricated using the optimized phosphors, and its emission spectrum widely overlaps with the absorption band of plant pigments. These results indicate that the Ca 2 YAl 3 Ge 2 O 12 : Eu 3+ phosphors possess great potential applications in plant growth LEDs.