Cr³⁺ Activated Garnet Phosphor with Efficient Blue to Far‐Red Conversion for pc‐LED

Abstract Far‐red (FR) phosphor‐converted light‐emitting diodes (pc‐LEDs) driven by blue LED chips are novel light sources for applications in phototherapy, photosynthesis, natural light simulation, and so on but still bear low electricity‐to‐FR light conversion efficiency (≤ 23%) due to deficiency of phosphors that have both high blue light absorptance and high FR internal quantum efficiency (IQE) for the realization of efficient blue to FR conversion. FR Ca₃Sc₂Si₃O₁₂ (CSSG):Cr³⁺ garnet phosphor has ultra‐high IQE (> 90%) but low blue light absorption. Here, a twofold increase of blue light absorption cross‐section is reported with still high FR IQE via Lu³⁺−Mg²⁺ substitution for Ca²⁺−Sc³⁺ in CSSG:Cr³⁺ to form Ca_3–xLu_xMg_xSc_2–xSi₃O₁₂:Cr³⁺ garnet solid solution, which is attributed to enhanced mixing of odd‐parity configuration into 3d configuration of Cr³⁺ induced by the cations substitution. Optical properties, crystal field strengths, and thermal stabilities of the solid solution phosphors are studied as a function of x. After complete replacement of Sc³⁺, the as‐fabricated FR pc‐LED emits at 750 nm with 65.7% blue‐to‐FR quantum conversion efficiency and consequently offers an electricity‐to‐FR light conversion efficiency over 30%. Moreover, the solid solution phosphors show high quenching temperatures in the range of 580–610 K. The results can advance the development of efficient FR phosphors and pc‐LEDs for various applications.