Photoluminescence and Structural Analysis of Samarium Doped TiO<sub>2</sub> Thin Films and Their Applications to Visible LEDs

Abstract

Samarium-doped anatase TiO 2 (A-TiO 2 :Sm) and rutile (R-TiO 2 :Sm) single phase thin films are fabricated by laser ablation and post-annealing at different temperatures. A-TiO 2 :Sm samples exhibit intense PL emission, whilst R-TiO 2 :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 Sm 3+ thin films annealed at 600˚C to 800˚C, which possess an activated semi-stable Sm 3+ ions luminescent center, dramatically changes from having high symmetry to low symmetry. While the phase transitioned R-TiO 2 :Sm and fabricated as R-TiO 2 :Sm samples showed highly symmetric. Hence, the coordination around the doped-Sm 3+ 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 Sm 3+ ions and PL intensity, and optical and electrical properties of a n +-ITO/TiO 2 :Sm/p-NiO/p +-Si hetero junction LED preparing with optimal fabricating condition.

Photoluminescence Enhancement and Change in the Second Nearest Neighbor Distance of Sm‐Doped TiO2 Thin Films

“…For the emitting samples, the EXAFS fitting reveals a distortion in the bond lengths. This is consistent with our previous work, which showed the window of annealing temperatures for efficient Sm‐related emission is the range 400 to 900 °C . This indicates a low symmetry model, in which each of the F. N. N. and the S. N. N. has different bond lengths.…”

“…Every spectrum appeared at the same peak position as the standard, indicating that Sm ions formed, in TiO 2 matrix, in the triply ionized state for all samples in the series. XAFS measurements were also carried out for other samples in R‐TiO 2 series, however as no further changes in the R‐TiO 2 samples with increased annealing temperatures was already reported, we select three different R‐TiO 2 samples for comparison with the A‐TiO 2 sample series.…”

“…Rare earth elements in crystalline host dielectrics show strong and sharp emission spectra, across a wide range of visible and near‐IR wavelengths and have thus attracted much attention in recent years as potential phosphor materials for lighting applications. Rare earth‐doped wide band gap semiconductors are particularly interesting because of their application in LEDs and other optoelectronic devices . In this study, Sm was selected as a luminescent center, which exhibits intense emission bands in the red and near‐IR wavelength regions.…”

PMMA as an Additive for Nanostructured TiO2 Thin Films for Heterojunction Visible-Blind Photodetectors

“…The TiO 2 thin films/nanostructure-based photodetectors reported so far are either of very high responsivity at the cost of a very long response time (∼10 s of seconds) or have a very low responsivity value with comparatively fast response time (∼ms). , The reason is that very high responsivity is achieved in such devices through trap-assisted photoconductive gain, which in turn makes the response time of the devices very long. To address the growing demands of fabrication of TiO 2 -based photodetectors with high detectivity/responsivity along with fast response time, some attempts have been made by doping TiO 2 with various metal ions, e.g., N, In, Y, Er, Cu, etc., − and by depositing epitaxial TiO 2 on LaO and GaN crystals through magnetron sputtering, CVD, etc. , However, these are very expensive techniques. In the present work, the problems mentioned above are addressed by employing a simple yet inexpensive technique.…”

Optimization of Crystal Structure Based on Experimentally Obtained XRD Patterns for Fluorescence of Sm<sup>3+</sup>-Doped TiO<sub>2</sub> Thin Films by Machine Learning

“…Of these, rutile and anatase types of titanium oxide (TiO 2 ) thin films are the most likely candidates. In our group's previous research [9] [10] [11] [12] [13], we found that the best way to increase the luminescence derived from RE ions is to add them to anatase TiO 2 (A-TiO 2 ), and when Sm 3+ or Nd 3+ ions are added to TiO 2 , they replace the Ti sites and are incorporated into the TiO 2 matrix. According to a detailed X-ray absorption fine structure (XAFS) analysis, the difference in luminescence is explained by the change in the ligand structure of the REs when added to the rutile and anatase crystal lattices.…”