TITLE:
Photoluminescence and Structural Analysis of Samarium Doped TiO2 Thin Films and Their Applications to Visible LEDs
AUTHORS:
M. Murayama, K. Yoda, K. Shiraishi, S. Guan, S. Komuro, X. Zhao
KEYWORDS:
Rare-Earth, Semiconductor, Photoluminescence, XAFS, LEDs
JOURNAL NAME:
Optics and Photonics Journal,
Vol.8 No.5,
May
31,
2018
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.