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Title: Concentration effect of H/OH and Eu{sup 3+} species on activating photoluminescence from ZnO:Eu{sup 3+} thin films

We identified the conditions necessary for photoluminescence from Eu{sup 3+} ions doped in ZnO thin films to occur via indirect excitation of ZnO host crystal with a 325-nm laser light. The ZnO:Eu films were sputter-deposited on Si(100) substrates at room temperature with H{sub 2}O vapor flowing as the oxygen source gas. A very narrow emission peak at 612 nm, assigned to {sup 5}D{sub 0}−{sup 7}F{sub 2} transition of Eu{sup 3+} ions, appeared after annealing at 200–300 °C in a vacuum or at 500 °C in an O{sub 2} ambient. At temperatures higher than these, the 612-nm emission peak attenuated and emission spectra exhibited weaker double peaks at 612 and 620 nm. This observation suggested that most Eu{sup 3+} ions withdrew from the most emission-active sites, and occupied two distinct chemical sites. With further increasing temperature, the double peaks merged to become broader, indicating that Eu{sup 3+} ions occupied sites more randomly. Emission intensity was the highest at an Eu content of 0.9 at. % and concentration quenching was observed as Eu content was increased. Substitution of Zn{sup 2+} cation sites with Eu{sup 3+} ions was confirmed from the primary X-ray diffraction peaks of ZnO(002); the ZnO lattice expanded as largermore » numbers of Eu{sup 3+} ions were incorporated. After the films were post-annealed at high temperatures, the diffraction angles approached those of undoped ZnO crystals, which reflected shifting Eu{sup 3+} ions into grain boundaries. The photoabsorption of OH species within a wavelength range of 2700–3000 nm and the Eu{sup 3+} emission intensity revealed correlated behavior. These results confirmed that the presence of OH and/or H species in the film is necessary for emissions from Eu{sup 3+} ions to appear. When OH and/or H species were diminished after high-temperature annealing, Eu{sup 3+} ions existing at substitutional sites became unstable and their emissions were consequently deactivated. The origin of emission-active Eu{sup 3+} ions can be explained in terms of either the defect mediated energy transfer model or the substitutional model.« less
Authors:
 [1] ;  [2]
  1. NTT Microsystem Integration Laboratories, 3-1 Morinosato Wakamiya, Atsugi, Kanagawa 243-0198 (Japan)
  2. Kurume National College of Technology, 1-1-1 Komorino, Kurume, Fukuoka 830-8555 (Japan)
Publication Date:
OSTI Identifier:
22217914
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 114; Journal Issue: 15; Other Information: (c) 2013 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ANNEALING; CATIONS; CRYSTALS; DOPED MATERIALS; EMISSION SPECTRA; ENERGY TRANSFER; EUROPIUM IONS; EXCITATION; GRAIN BOUNDARIES; PHOTOLUMINESCENCE; QUENCHING; SPUTTERING; THIN FILMS; WATER VAPOR; X-RAY DIFFRACTION; ZINC IONS; ZINC OXIDES