Crystallization of Na₂SrGe₆O₁₄:Cr³⁺,Yb^{3+ Glass Ceramics Enabling a Watt-Level Output Power NIR-I/NIR-II Lighting Source}

Near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) lighting sources are applied in non-destructive examination and illumination supplements for night monitoring. As a critical component of NIR pc-LED, NIR phosphors are required to possess a high external quantum efficiency (EQE), super thermal stability, and broadband emission to meet applications. Here, Na2SrGe6O14:Cr3+ (NSGO:Cr) glass ceramics (GC) bulk via highly crystallization from glass precursor is fabricated and demonstrates an ultrabroad emission band centered at 815 nm with a full width at half-maximum (FWHM) of 214 nm and a high EQE of 49.2%. Moreover, Yb3+ co-doping significantly enhances Cr3+ -> Yb3+ energy transfer (ET) due to the stronger Yb3+: F-2(7/2)-F-2(5/2) absorption. Benefiting from the ET process, the Cr/Yb co-doped GC exhibits NIR-I/II emission with improved thermal stability from 30.1% to 65.0%. Furthermore, an encapsulant-free NIR GC-converted LED (GCc-LED) is prepared and exhibits 52.2 mW NIR output power with a high photoelectric conversion efficiency (PCE) of 19.4%. Under a large current of 600 mA, the NIR device exhibits a watt-level output power of 922.4 mW with a PCE of 9.1%. Compared to conventional NIR powder phosphors, NSGO:Cr/Yb GC with high performance can open up an avenue for the fabrication of high power NIR lighting sources.