Effects of annealing temperature and Eu concentration on structural and photoluminescence properties of Eu-doped SnO2 thin films

Significance 

Semiconductors can be defined as partially conductive solids; i.e. possess electrical conductivity between that of a conductor and an insulator. Rare earth-doped semiconductors have been known to exhibit sharp intra-4f optical transitions at emission wavelengths ranging from the infrared to ultraviolet regions of the UV spectrum depending on the rare-earth element used. The excitation mechanisms due to the rare-earth elements in host materials are generally divided into direct and indirect types. The former has a low excitation efficiency because intra-4f optical transitions are electric dipole forbidden while in the latter, excitation of rare-earth ions is induced by carrier-mediated energy transfer from the host semiconductor. Among various wide-gap semiconductors, SnO2 is a promising host material. SnO2 is n-type wide-gap semiconductor with excellent chemical and mechanical stability. In particular, there have been many reports on the phosphor properties of Eu-doped SnO2 nanoparticles that exhibit red emission. Unfortunately, the effects of fabrication conditions on the properties of Eu-doped SnO2 thin films prepared by metal organic decomposition have not been thoroughly studied.

Recently, a research paper authored by Associate Professor Junji Sawahata from the National Institute of Technology, Ibaraki College assessed the effects of annealing temperature and Europium (Eu) concentration on the structural and optical properties, particularly luminescence properties, of Eu-doped SnO2 thin films prepared by metal organic decomposition. He offered to utilize the metal organic decomposition (MOD) process since it was an attractive process for preparing oxide thin films owing to its simple fabrication approach that involved spin-coating of MOD solutions and annealing. His work is currently published in the research journal, Thin Solid Films.

In brief, the research method employed commenced with Eu-doped SnO2 thin films preparation using the MOD technique. The mixed solution utilized was spin-coated onto silicone substrates that were cleaned with UV/ozone irradiation. The spin-coated samples were then dried and subsequently annealed in unique atmospheric conditions. The researcher then evaluated the prepared samples’ structural properties by X-ray diffraction. He then performed Fourier transform infrared spectroscopy measurements. Lastly, he characterized the surface morphology of the samples by atomic force microscopy after which he undertook photoluminescence measurements.

The author found out that the films had a tetragonal rutile crystal structure, and the crystallinity improved with increasing annealing based on the various measurements he had undertaken. Additionally, he noted that structural deterioration and a change in bond energy were observed with increasing Eu concentration. He also observed that concentration quenching occurred when the Eu concentration exceeded 7.2 at.%.

In summary, the study by Associate Professor J. Sawahata presented successful preparation of Eu-doped SnO2 thin films by the MOD method through a pyrolysis of organic acid salts. In general, he investigated the effects of annealing temperature and Eu concentration on the structural and photoluminescence (PL) properties. Altogether, the results he obtained pointed out that the PL and structural properties of Eu-doped SnO2 thin films prepared using this technique were strongly dependent on the annealing temperature and the Eu concentration.

About the author

Dr. Junji Sawahata

Associate Professor, National Institute of Technology, Ibaraki College, Japan. 2007, Ph.D. in Engineering, University of Tsukuba.

Research interests include the fabrication and characterization of transparent conductive oxides and rare earth doped semiconductors.

Reference

Junji Sawahata. Effects of annealing temperature and Eu concentration on the structural and photoluminescence properties of Eu-doped SnO2 thin films prepared by a metal organic decomposition method. Thin Solid Films, volume 656 (2018) page 1–5.

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