Fe–Li complex emission in ZnO

In this work, we report on three new extremely sharp emission lines in zinc oxide (ZnO) related to iron–lithium complexes. The identification is based on a comparison of hydrothermally grown ZnO with high lithium concentration and a lithium-free sample grown by methane based chemical vapor deposition, which both were implanted with iron. After annealing in a mixed oxygen/argon atmosphere at 800 ° C, the lithium-free sample showed no additional lines besides the well-known emission at 693 nm ( 1.7873 4 eV ), whereas the hydrothermally grown sample emitted three intense and sharp lines in photoluminescence (PL) spectroscopy. These emission lines at 705 nm ( 1.7587 3 eV ), 712 nm ( 1.7415 3 eV ), and 732 nm ( 1.6928 3 eV ) were characterized by temperature dependent high resolution continuous wave (cw) and time-resolved PL spectroscopy, as well as by photoluminescence excitation spectroscopy, and are assigned to different Fe–Li complexes. We find a single thermally activated excited state for each of the complex emission lines, different from the 4 T 1 → 6 A 1 transition of Fe 3 + with its at least three excited states. While time-resolved photoluminescence measurements of the Fe 3 + transition show a lifetime of 24.9 ± 0.5 ms, we find a reduced lifetime of 8.5 ± 1 ms for the new zero phonon lines, pointing to stronger mixture of the Fe 3d states with surrounding p-orbitals.