Broadband near‐infrared (NIR) phosphor‐converted light emitting diode (pc‐LED) is demanded for wearable biosensing devices, but it suffers from low efficiency and low radiance. This study reports a broadband NIR Ca3‐xLuxHf2Al2+xSi1−xO12:Cr3+ garnet phosphor with emission intensity enhanced by 81.5 times. Chemical unit co‐substitution of [Lu3+−Al3+] for [Ca2+−Si4+] is responsible for the luminescence enhancement and further alters the crystal structure and electronic properties of the garnet. Using the optimized phosphor, a NIR pc‐LED with photoelectric efficiencies of 21.28%@10 mA, 15.75%@100 mA and NIR output powers of 46.09 mW@100 mA, 54.29 mW@130 mA is fabricated. The high power NIR light is observed to penetrate upper arms (≈8 cm). For application in NIR spectroscopy, the NIR pc‐LED is used as light source to measure transmission spectra of water, alcohol, and bovine hemoglobin solution. These results indicate the NIR garnet phosphor to be a promising candidate for NIR pc‐LED.

The garnet Ca2LuZr2Al3O12 (CLZA) is a promising broad-band NIR phosphor for blue LED chips when it is doped with Cr3+.

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 Ca3–xLuxMgxSc2–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.