Strategies to Realize Efficient and Stable Broadband NIR Emission in Germinate Oxides

Abstract Phosphor‐converted light‐emitting diodes (pc‐LEDs) are efficient and cost‐effective ultrabroadband light sources for miniaturizing various optical systems, but they exhibit poor optical performance due to the lack of efficient near‐infrared (NIR) phosphors with a wide spectral coverage of 700−1100 nm. Although germanate oxides are a promising class of host materials for Cr 3+ to generate broadband NIR light, the preferred formation of [CrO 4 ] 4− and the high vapor pressure of Ge element cause these Cr 3+ activated phosphors to suffer from low internal quantum efficiency (IQE) and poor thermal stability. Here, highly efficient (IQE > 90%) and thermally stable broadband NIR emission of Cr 3+ in the germinate garnet Ca 2 LuMgScGe 3 O 12 (CLMSG) are obtained by exploiting a two‐step sintering method to achieve full reduction of Cr 4+ to Cr 3+ . Further, efficient energy transfer from Cr 3+ to Yb 3+ is leveraged to significantly improve the emission intensity of CLMSG:Cr 3+ in the shortwave infrared range of 900−1100 nm. Finally, an ultrabroadband NIR pc‐LED with a high NIR conversion efficiency (21.5%@10 mA) and high NIR power (116.4 mW@350 mA) is demonstrated to verify the strong capability of CLMSG:Cr 3+ , Yb 3+ in blue‐to‐NIR light conversion. The results open up new ways to realize efficient ultrabroadband NIR‐emitting materials.