Fe–Li complex emission in ZnO

Abstract

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 693nm (1.78734eV), whereas the hydrothermally grown sample emitted three intense and sharp lines in photoluminescence (PL) spectroscopy. These emission lines at 705nm (1.75873eV), 712nm (1.74153eV), and 732nm (1.69283eV) 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 4T1→6A1 transition of Fe3+ with its at least three excited states. While time-resolved photoluminescence measurements of the Fe3+ transition show a lifetime of 24.9±0.5ms, we find a reduced lifetime of 8.5±1ms for the new zero phonon lines, pointing to stronger mixture of the Fe 3d states with surrounding p-orbitals.

Enhanced Thermal Diffusivity and Photocatalytic Dye Degradation Capability of Zinc Ferrite/Silver/Silver Chloride Nanocomposites

“…The strong and sharp red emission obtained around 734nm for CS0 and CS1 samples (Fig. 6) can be attributed to the stronger admixture of p-states of the neighboring oxygen atoms into the Fe 3+ d-states by virtue of the shorter lattice parameter in the presence of chloride ions as given in reports [21] which also confirms the proportion of AgCl in CS0 and CS1 given in XRD and EDAX results. A weak green emission around 533nm is due to the recombination of electrons deeply trapped in oxygen vacancies in the zinc ferrite with photogenerated holes.…”

Growth and Structure of Single-Crystal ZnO Nanorods Codoped with Fe and Li for Multiferroic Applications

“…38 ZnO nanorods with 2.05% Fe and 1.95% Li exhibit strong luminescence due to dopant defects, and band-to-band transition and luminescence are strongly suppressed due to more efficient recombination through deep levels associated with Li and Fe. The emission band covering the range from 2.0 eV (600 nm) to 1.7 eV (730 nm) is associated with a series of differently charged complexes Fe Zn −Li Zn and Li−O complexes 32,55 as well as complexes Fe Zn 3+ ions. 56 Velaźquez et al 57 showed that the NIR emission band covering the range from 1.7 eV (730 nm) to 1.4 eV (880 nm) arises due to radiative transitions in Li−Li nanoclusters located in ZnO interstices.…”

“…XAS research by Giuli et al 30 demonstrated aliovalent substitution of Fe 3+ for Zn 2+ in Zn 0.9 Fe 0.1 O samples accompanied by the formation of cationic vacancies or interstitial oxygen around incorporated Fe 3+ ions for charge compensation. Kutin et al 31 and Muller et al 32 reported EPR and photoluminescence research on Fe 3+ −Li + complexes in ZnO, where Fe 3+ and Li + ions substitute for Zn 2+ sites in the same basal plane, and Fe 3+ and Li + ions substitute for Zn 2+ in an axial cationic site and one of the nearest basal plane sites, and vice versa. Regarding lithiation of Zn 0.9 Fe 0.1 O, Giuli et al 33 wrote that cationic vacancies play a crucial role upon initial lithiation leading to partial reduction of Fe 3+ to Fe 2+ ions.…”