A High‐Crystallinity Transparent Glass‐Ceramic Enables Encapsulant‐Free, High Quantum Efficiency NIR‐II Miniature Light Source

Abstract The second near‐infrared (NIR‐II) light source is of considerable importance for broad frontier applications in biomedical imaging, non‐destructive testing, and night vision. However, the conventional phosphor‐converted light‐emitting diodes (pc‐LEDs) require polymer encapsulants, which impose a fundamental limitation on NIR‐II light sources owing to severe reabsorption and restricting output power. To overcome this challenge, a monolithic MgGa 2 O 4 :Cr 3+ /Ni 2+ glass‐ceramic is demonstrated that serves as a highly transparent, encapsulant‐free converter. Through precise microstructural control to suppress preferential crystal orientation, the glass‐ceramic achieves ≈90% transmittance together with efficient Cr 3+ to Ni 2+ energy transfer. The resulting glass‐ceramic converted LED (GCc‐LED) delivers intense broadband emission across NIR‐II regions with an ultra‐high external quantum efficiency of 49.4%, and a high NIR output power of 114.1 mW (at 320 mA) is obtained. It also shows excellent thermal stability with a high activation energy of 0.39 eV. The superior performance of the GCc‐LED in high‐contrast bioimaging, night vision, and non‐destructive sensing is further demonstrated. This work establishes an effective way to overcome the material constraint of traditional pc‐LEDs and shows great promise for the development of high‐power, miniature NIR‐II light sources.