Deep‐Red Ca₃Al₂Ge₃O₁₂:Eu³⁺ Garnet Phosphor with Near‐Unity Internal Quantum Efficiency and High Thermal Stability for Plant Growth Application

Abstract Trivalent europium (Eu³⁺) doped phosphors usually radiate orange or red light owing to distinct transitions from the ⁵D₀ excited level to the ground states of ⁷F₁ and ⁷F₂. However, Eu³⁺ activated phosphors with a dominant deep‐red emission due to ⁵D₀→⁷F₄ transition are relatively rare. In this work, the synthesis and photoluminescence properties of Ca₃Al₂Ge₃O₁₂:Eu³⁺ deep‐red phosphor with an intense ⁵D₀→⁷F₄ transition are reported. Irradiating this new garnet phosphor with 394 nm near‐ultraviolet light generates a dominant deep‐red emission band centered at 707 nm. The phosphor has a high internal quantum efficiency of 98.4% and excellent luminescence thermal stability, maintaining 78.8% of the room temperature emission intensity at 150 °C. Based on the unique spectral feature of this new compound, a phosphor‐converted deep‐red LED prototype device is fabricated, producing an output power of 27.3 mW with a photoelectric conversion efficiency of 4.0% at 200 mA. Plant growth experiments are also conducted to demonstrate the obvious positive effects of the fabricated deep‐red LED on plant growth, further indicating that the as‐prepared Ca₃Al₂Ge₃O₁₂:Eu³⁺ deep‐red phosphor can act as a promising luminescence converter for plant growth LED bulbs.