The 4 T 1 (F) → 4 A 2 (F) Luminescence of the Co 2+ (d 7 ) Impurity Centre in Zinc Selenide Crystals

The 4 T 1 (F) → 4 A 2 (F) transition of Co 2+ (d 7 ) ions in ZnSe is detected by its emission at T ≈ 4 K. The no‐phonon line at v̄ = 5558 cm −1 is demonstrated to coincide with the inverse absorption transition. The luminescence shows medium coupling to ZnSe lattice vibrations. An exponential decay with a time constant τ = 100 μs is recorded. A rich fine‐structure is displayed by the 4 T 1 (P) ← 4 A 2 (F) absorption studied for comparison. Qualitatively, it can be described by spin–orbit and Jahn‐Teller interaction. Finally, the properties of two additional emission bands present in the 4200 to 5600 cm −1 region are illustrated, one of them dominated by a no‐phonon line at 5471 cm −1 . Capture of a hole by a neutral donor is discussed as a possible interpretation of a broad luminescence band peaking near 4600 cm −1 .