Distinguishing Between Thermal Coupling and Spin Interaction for Cr³⁺ NIR Luminescence Through Temperature‐Dependent Lifetime Analysis

Abstract Octahedrally coordinated Cr 3+ ions have been well‐documented for exceptional near‐infrared (NIR) luminescence properties, originating from intra‐configurational d ‐ d transition. While broadband emissions within intermediate crystal fields have been tentatively attributed to either thermally coupled excited states or Cr 3+ ‐Cr 3+ spin interaction. A definitive delineation of the underlying mechanism governing these two luminescence behaviors remains contentious. In this study, this controversy based on the thermal evolution of decay lifetime in gallate garnet and magnetoplumbite lattices is resolved. The temperature‐dependent time decay rate within intermediated crystal fields is evaluated, employing a numerical simulation within a two‐level model framework. The results reveal that the broadband luminescence in Y 3 Ga 5 O 12 :Cr 3+ stems from the thermal coupling of 2 E and 4 T 2 excited states, in which the thermal population of 4 T 2 state by the longer‐lived 2 E level resulted in a pseudo‐exponential decrease in the lifetime as a function of temperature. In contrast, these lifetimes of SrGa 12 O 19 :Cr 3+ and LaMgGa 11 O 19 :Cr 3+ exhibit a significantly slower decay rate with temperature, indicating the emergence of spin interaction, which is verified by calculating the spin interaction energy. Therefore, the works provide an easy‐handle analytical framework to distinguish the physical mechanism of Cr 3+ luminescence in intermediate crystal fields using temperature‐dependent lifetime analysis.