Identifying Near‐Infrared Persistent Luminescence in Cr³⁺‐Doped Magnesium Gallogermanates Featuring Afterglow Emission at Extremely Low Temperature

Room‐temperature persistent phosphors emitting in a wide spectral range are extensively explored owing to their commercial interest in applications such as night‐vision signs and medical imaging. However, phosphors featuring long‐lasting near‐infrared emission at extremely low temperature are barely reported so far. Herein, a design of trivalent chromium‐activated magnesium gallogermanates (Mg 1+ x Ga 2−2 x Ge x O 4 :Cr 3+ ) is demonstrated that exhibit strong near‐infrared afterglow emission at low temperature, e.g., −80 °C. Notably, this new persistent phosphor can be efficiently activated even at these low temperatures. A combination of experimental characterizations together with simulations has identified its novel low‐temperature persistent luminescence and good capacity of stabilizing a large number of very shallow traps. The finding of this low‐temperature near‐infrared afterglow property opens up a new frontier for exploring persistent phosphors and provides an opportunity for novel applications at extreme conditions, such as cryopreservation of biological samples.