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

Abstract

Octahedrally coordinated Cr3+ 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 Cr3+‐Cr3+ 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 Y3Ga5O12:Cr3+ stems from the thermal coupling of 2E and 4T2 excited states, in which the thermal population of 4T2 state by the longer‐lived 2E level resulted in a pseudo‐exponential decrease in the lifetime as a function of temperature. In contrast, these lifetimes of SrGa12O19:Cr3+ and LaMgGa11O19:Cr3+ 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 Cr3+ luminescence in intermediate crystal fields using temperature‐dependent lifetime analysis.