Dual Divalent Cations‐Doped Near‐Infrared Garnet Phosphors with Charge Compensation and Surface Modification for Next‐Generation Broadband Fiber Amplifiers

Abstract Near‐infrared (NIR)‐II phosphor‐converted light‐emitting diodes (NIR‐II pc‐LEDs) have been extensively developed using NIR‐II phosphor with commercial LEDs. However, the application of NIR‐II phosphor in optical communications remains underexplored. In this work, a phosphor series of Y 3−x−y Al 4.9 O 12 :0.1Cr,xCa 2+ ,yMg 2+ is simultaneously tuned with Mg 2+ and Ca 2+ , resulting in Y 2.76 Al 4.9 O 12 :0.1Cr,0.16Ca 2+ ,0.08Mg 2+ (YAG:0.1Cr,0.16Ca,0.08Mg) crystal fiber, with a length of 2.65 cm and a diameter of 216.95 µm, is grown from the optimized phosphor. The fabrication process involved phosphor synthesis, pellet production, and crystal fiber growth using the laser‐heated pedestal growth method. Proposed dual cations modification allowed to i) enhance NIR‐II broadband emission in 1100–1600 nm by improving the structure due to the incorporation of Mg 2+ ions and ii) provide additional tetrahedral sites for Cr 4+ ions via Mg 2+ /Ca 2+ introduction. The YAG:0.1Cr,0.16Ca,0.08Mg crystal fiber exhibits promoted luminescence compared with the commercial Cr 4+ ‐doped Y 3 Al 5 O 12 crystal fiber, indicating its potential as a fiber amplifier in optical communications.