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Title: Luminescence properties of lanthanide and ytterbium lanthanide titanate thin films grown by atomic layer deposition

Lanthanide based luminescent materials are highly suitable as down conversion materials in combination with a UV-absorbing host material. The authors have used TiO{sub 2} as the UV-absorbing host material and investigated the energy transfer between TiO{sub 2} and 11 different lanthanide ions, Ln{sup 3+} (Ln = La, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb) in thin films grown by atomic layer deposition. They have also investigated the possibility to improve the overall energy transfer from TiO{sub 2} to Yb{sup 3+} with a second Ln{sup 3+}, in order to enhance down conversion. The films were grown at a substrate temperature of 300 °C, using the Ln(thd){sub 3}/O{sub 3} (thd = 2,2,6,6-tetramethyl-3,5-heptanedione) and TiCl{sub 4}/H{sub 2}O precursor pairs. The focus of the work is to explore the energy transfer from TiO{sub 2} to Ln{sup 3+} ions, and the energy transfer between Ln{sup 3+} and Yb{sup 3+} ions, which could lead to efficient down conversion. The samples have been characterized by x-ray diffraction, x-ray fluorescence, spectroscopic ellipsometry, and photoluminescence. All films were amorphous as deposited, and the samples have been annealed at 600, 800, and 1000 °C in order to investigate the correlation between the crystallinity and luminescence. The lanthanum titanium oxide samples showed a weakmore » and broad emission centered at 540 nm, which was absent in all the other samples, indicating energy transfer from TiO{sub 2} to Ln{sup 3+} in all other lanthanide samples. In the amorphous phase, all samples, apart from La, Tb, and Tm, showed a typical f-f emission when excited by a 325 nm HeCd laser. None of the samples showed any luminescence after annealing at 1000 °C due to the formation of Ln{sub 2}Ti{sub 2}O{sub 7}. Samples containing Nd, Sm, and Eu show a change in emission spectrum when annealed at 800 °C compared to the as-deposited samples, indicating that the smaller lanthanides crystallize in a different manner than the larger lanthanides. Energy transfer from Ln{sup 3+} to Yb{sup 3+} was observed neither in the amorphous or annealed samples. On the other hand, Yb{sup 3+} was found to be an efficient sensitizer for Ho{sup 3+}'s 1200 nm emission.« less
Authors:
; ;  [1] ;  [2]
  1. Department of Chemistry, Centre for Materials Science and Nanotechnology, University of Oslo, Sem Sælandsvei 26, 0371 Oslo (Norway)
  2. Department of Physics, Centre for Materials Science and Nanotechnology, University of Oslo, Sem Sælandsvei 24, 0371 Oslo (Norway)
Publication Date:
OSTI Identifier:
22489763
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Vacuum Science and Technology. A, Vacuum, Surfaces and Films; Journal Volume: 34; Journal Issue: 1; Other Information: (c) 2015 American Vacuum Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; AMORPHOUS STATE; ANNEALING; ENERGY TRANSFER; FLUORESCENCE; HOLMIUM IONS; LANTHANUM; PHOTOLUMINESCENCE; SENSITIZERS; THIN FILMS; TITANATES; TITANIUM CHLORIDES; TITANIUM OXIDES; X RADIATION; X-RAY DIFFRACTION; YTTERBIUM; YTTERBIUM IONS