Coupled trapping and de-trapping dynamics govern spectral evolution in multi-center luminescent systems

In luminescent materials, excitation-time-dependent spectral evolution in connection with nonequilibrium carrier dynamics often remain poorly understood. Here we show that coupled trapping and de-trapping processes govern this behavior in a multi-center luminescent system for the case of Sb³⁺ doped CsCdCl₃, featuring hexagonal and cubic phases. Especially in hexagonal CsCdCl₃:Sb³⁺, multiple emission centers and trap states form competing carrier transfer pathways under steady excitation, leading to a time-dependent redistribution of excitation energy. Trapping introduces spectrally selective absorption overlapping the green Sb³⁺ emission, resulting in trap-assisted reabsorption, while optically stimulated de-trapping preferentially feeds the lower energy Cd-Cl orange-near-infrared emission. The competition among trapping, trap-assisted reabsorption, and de-trapping establishes a dynamic steady state that continuously reshapes the emission spectrum. These results identify coupled trapping and de-trapping dynamics as the microscopic origin of excitation-time-driven spectral evolution in multi-emitter systems.