Crystallization of Na2SrGe6O14:Cr3+,Yb3+ Glass Ceramics Enabling a Watt‐Level Output Power NIR‐I/NIR‐II Lighting Source

Abstract 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, Na 2 SrGe 6 O 14 :Cr 3+ (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, Yb 3+ co‐doping significantly enhances Cr 3+ → Yb 3+ energy transfer (ET) due to the stronger Yb 3+ : 2 F 7/2 ‐ 2 F 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.