Abstract
Samarium-doped anatase TiO2 (A-TiO2:Sm) and rutile (R-TiO2:Sm) single phase thin films are fabricated by laser ablation and post-annealing at different temperatures. A-TiO2:Sm samples exhibit intense PL emission, whilst R-TiO2:Sm samples exhibit weak PL emission. The local crystal structure of Sm-dopants is investigated using X-ray absorption fine structure (XAFS) measurements. The thin films showing strong PL emission have lower crystal symmetry than the other samples, which show weak PL emission. We report the relationship between changing the symmetry of the local structure and activation of the luminescent center. The local structure of Sm3+ thin films annealed at 600°C to 800°C, which possess an activated semi-stable Sm3+ ions luminescent center, dramatically changes from having high symmetry to low symmetry. While the phase transitioned R-TiO2:Sm and fabricated as R-TiO2:Sm samples showed highly symmetric. Hence, the coordination around the doped-Sm3+ ions is the key factor for exhibiting an intense PL emission. Therefore, activation of the luminescent center is strongly connected with the distorted local crystal symmetry, which is proposed as one of the factors defining the transfer probability. In this work, we discuss the connection between coordination around Sm3+ ions and PL intensity, and optical and electrical properties of a n+-ITO/TiO2:Sm/p-NiO/p+-Si hetero junction LED preparing with optimal fabricating condition.
Highlights
The samples were annealed at different temperatures, and analyzed by X-ray diffraction (XRD), PL and X-ray absorption fine structure (XAFS)
The samples annealed at 700 ̊C of anatase TiO2 (A-TiO2) exhibited the strongest PL emission, and the samples annealed at 1100 ̊C of A-TiO2 and fabricated as R-TiO2 crystal phase showed a weak PL emission
The result of the XAFS analysis revealed the local structures of A- and R-TiO2
Summary
Rare earth element doped semiconductors and oxide materials have been studied. The chemical properties of both the doped rare earth and host materials can be considered to determine the atomic coordination of the doped rare earth element-O luminescent center. This fact indicates that analyzing the symmetry of rare earth-O would enable determination of the optimal conditions for the production of applicable materials with a luminescent center
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