Developing the Na2CaZr2Ge3O12:Cr3+ Garnet Phosphor for Advanced NIR pc-LEDs in Night Vision and Bioimaging

Materials emitting near-infrared (NIR) light play a crucial role in the development of phosphor-converted light-emitting diodes (pc-LEDs) for applications ranging from fundamental science like spectroscopic analysis to highly applied uses like night vision and biological imaging. One class of materials that has garnered significant interest for these technical spaces is Cr3+-activated garnets due to their high efficiency and ability to operate at relatively high temperatures. However, their limited emission beyond 800 nm impedes their use as optimal blue LED-pumped NIR-emitting materials. In this study, we present a new garnet-type NIR phosphor, Na2CaZr2Ge3O12:Cr3+, that addresses this challenge─the material exhibits a long-wavelength emission (λem,max = 832 nm) and good thermal quenching resistance while maintaining an excellent internal quantum efficiency (IQE = 98%). These properties are attributed to a crystal environment reconstruction, where a crystal structure distortion is coupled to a weak crystal field, which is uncommon for most rigid garnet-type phosphors. Furthermore, the fabricated NIR pc-LED devices using this material demonstrate superior performance compared with devices employing well-known efficient NIR phosphors operating in this emission range. The light source is subsequently demonstrated in applications spanning night vision, bioimaging, and nondestructive analysis. This study not only provides insights into the luminescence properties of Cr3+-activated garnet materials with desirable performance but also highlights the practical application of NIR-emitting garnet phosphors.