Broadband Near‐Infrared Cr⁴⁺‐Doped Garnet Phosphors through Divalent Calcium Charge Compensation for Advanced Crystal Fiber Amplifiers

Abstract Near‐infrared‐II (NIR‐II) phosphors are extensively used as NIR phosphor‐converted light‐emitting diodes across various applications. Nonetheless, their application in fiber communication remains underexplored. Furthermore, efficiency challenges persist in developing broadband NIR crystal fiber amplifiers. A series of the Y 3− y Al 5− x O 12 : x Cr, y Ca 2+ phosphors with boosted Cr 4+ concentration via calcium charge compensation is synthesized, and the optimized sample is fabricated to crystal fibers to reveal the application of the NIR‐II phosphors to fiber communication. The fabricated Cr 4+ ‐doped crystal fiber, exhibiting broadband Cr 4+ emission within 1100–1600 nm, effectively covers the high‐transmission loss region caused by water absorption in the telecommunication band. Comprehensive characterization and analyses of the Cr 4+ are discussed. Y 2.84 Al 4.9 O 12 :0.1Cr,0.16Ca 2+ crystal fiber, fabricated through phosphor synthesis, pellets’ production, and the laser‐heated pedestal growth method, exhibits superior photoluminescence compared to the commercial Cr 4+ ‐doped Y 3 Al 5 O 12 crystal fiber. Here the potential of NIR‐II phosphors is highlighted in enhancing fiber communication and valuable insights for their future application are provided.