Transition metal chalcogenides, of which the polycrystalline Cr:ZnS is exemplary, have various applications as mid-IR laser media. An outstanding topic in these materials is direct electric pumping, which populates a charge transfer band. Understanding the relaxation pathways back to the ground state is crucial for optimizing laser emission. Here, we mimic the excitation of the high-lying charge transfer band (Cr + )* + h + ←Cr 2+ using a 400 nm pump and monitor the ground state bleach signal from the Cr 2+ ion using an 800 nm probe, i.e., the recovery of the ground state population following charge transfer. We find the excited state ion decays via two distinct timescales: a fast τ 1 (330 ± 30 fs) and a slower τ 2 (9.4 ± 0.5 ps) lifetime. These results identify the time-constants of ground state recovery which do not lead to population of the mid-IR lasing state ( 5 E ). The identification of these non-radiative pathways may aid the design of more efficient lasing media.
