研究者詳細 - 植田　和茂

論文 - 植田　和茂

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Host-to-Activator Energy Transfer Developed by Eu<sup>3+</sup> Doping at B Sites in Perovskite-Type Strontium Stannate Phosphor 査読有り国際誌

Ueda K., Ogata T., Nakamura K., Honma T.

Journal of Physical Chemistry C 128 ( 25 ) 10660 - 10667 2024年06月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

Site-selective doping and site-dependent luminescence of Eu3+ were examined in the perovskite-type strontium stannate host, SrSnO3, which is reported as a transparent oxide semiconductor (TOS). The X-ray diffraction patterns and the spectra of the X-ray absorption near edge structure (XANES) for the Eu L3 edge revealed that the site-selective doping of Eu3+ was achieved almost completely by Mg2+ and La3+ or Nb5+ codoping. The site-dependent Eu3+ luminescence was clearly observed in the codoped samples, and the luminescence derived from the magnetic dipole transitions from the 5D0 to 7F1 states was seen intensively from Eu3+ at the B sites, Eu3+(B). The intense luminescence from Eu3+(B) was found to occur only in the samples with a high Eu3+(B) proportion attained by La3+ or Nb5+ codoping. It is also noteworthy that the intense Eu3+(B) luminescence was obtained not by the charge transfer excitation for Eu3+(B) but by the excitation for the host of the SrSnO3 TOS, revealing the efficient energy transfer from the host to Eu3+(B). The finding indicates that both the Eu3+ luminescence and semiconducting features could be available in SrSnO3, which is preferable for optoelectronic applications such as cathodoluminescence and electroluminescence.

DOI： 10.1021/acs.jpcc.4c01967

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Site-Selective Eu<sup>3+</sup> Doping and Enhanced Luminescence from Eu<sup>3+</sup> at B Sites in Perovskite-Type Strontium Zirconate and Hafnate 査読有り国際誌

Ueda K., Ogata T., Mitsuda S., Nakamura K., Honma T.

Journal of Physical Chemistry C 127 ( 31 ) 15641 - 15647 2023年08月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

To achieve efficient Eu3+ luminescence, site-selective doping of Eu3+ was attempted in perovskite-type (ABO3) SrMO3 (M = Zr, Hf). In contrast to CaMO3 and BaMO3, it was found that the doping sites of Eu3+ (EuSr• or EuZr′/EuHf′) could be highly controlled in SrMO3 by a codoping technique. This was mainly because the size of Sr2+ was suitable for the site-selective doping of Eu3+ in SrMO3. The codoping of small Ga3+ at B sites (GaZr′/GaHf′) was carried out for A-site doping of Eu3+, whereas the codoping of large La3+ at A sites (LaSr•) or small Nb5+ at B sites (NbZr•/NbHf•) was conducted for B-site doping of Eu3+. As a result, the proportion of Eu3+ at A and B sites became more than 90% by the A-site and B-site doping, respectively, from the analysis of X-ray absorption near-edge structures for the Eu L3 edge. Eu3+ ions were driven to intentional sites by codoping due to the dual effects of charge compensation and ionic size balance. The high Eu3+ proportion at B sites, viz. the almost complete B-site doping, led to the findings of significant enhancement of Eu3+ luminescence, which was derived from the magnetic dipole transitions from 5D0 to 7F1 states. The quantum efficiencies of the enhanced luminescence from SrMO3 doped with Eu3+ at B sites exceeded 50% at room temperature.

DOI： 10.1021/acs.jpcc.3c03621

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Site-Dependent Luminescence from Pr<sup>3+</sup> in Double-Perovskite-Type Alkaline Earth Lanthanum Tantalates 査読有り国際誌

Ueda K., Oya A., Nagashima S., Ogata T., Honma T., Omata T.

Journal of Physical Chemistry C 127 ( 18 ) 8833 - 8839 2023年05月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

Site-dependent photoluminescence (PL) from Pr3+ was investigated in Pr3+-doped alkaline earth lanthanum tantalates with a double-perovskite-type structure (AA’)[BB’]O6. Pr3+ was partly substituted for La3+ in both (CaLa)[CaTa]O6 (CLTO) and (Ba2)[LaTa]O6 (BLTO). The results of X-ray absorption near-edge structure of the Pr L3 absorption edge strongly supported that Pr3+ ions were located at A sites in CLTO:Pr3+ and at B sites in BLTO:Pr3+. In the PL excitation (PLE) spectra, both CLTO:Pr3+ and BLTO:Pr3+ showed intense peaks in the UV region, which were assignable to the 4f-5d transitions in Pr3+. The energy for the 4f-5d excitation peak in BLTO:Pr3+ was found to be lower than that in CLTO:Pr3+, which was primarily attributed to the low energy of Pr3+ 5d states resulted from a large crystal field at B sites. On the Pr3+ 4f-5d excitation by UV light, CLTO:Pr3+ showed white PL due to the transitions from both 3PJ and 1D2 levels, whereas BLTO:Pr3+ exhibited red PL caused by the transitions from only 1D2 levels. The low energy of Pr3+ 5d states at B sites was responsible for the quenching of the blue-green luminescence from 3PJ levels in BLTO:Pr3+

DOI： 10.1021/acs.jpcc.3c01208

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Effects of Codoping on Site-Dependent Eu<sup>3+</sup> Luminescence in Perovskite-Type Calcium Zirconate and Hafnate 査読有り国際誌

Ueda K., Ogata T., Honma T.

Inorganic chemistry 62 ( 5 ) 2146 - 2152 2023年02月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

The single doping of Eu3+ and codoping with Ga3+ or La3+ into perovskite (ABO3)-type CaZrO3 and CaHfO3 were carried out to investigate the effect of codoping on the photoluminescence (PL) features of Eu3+, attempting the site-selective Eu3+ doping at either A or B sites. To comprehend the Eu3+ PL features, the accurate locations of Eu3+ were examined by X-ray absorption near edge structure (XANES) and the proportions of Eu3+ located at A or B sites (Eu3+(A) or Eu3+(B); EuCa• or EuZr'/EuHf') were analyzed. No considerable differences in the XANES spectra and in the proportions of Eu3+(A) and Eu3+(B) were observed in the single-doped samples. On the other hand, the shape of the XANES spectra and the Eu3+ proportion markedly differed in the codoped samples. Ga3+ codoping (GaZr'/GaHf') achieved Eu3+(A) proportions of more than 90%, and La3+ codoping (LaCa•) resulted in the largest Eu3+(B) proportions of approximately 40%. In both PL and PL excitation spectra, the site-dependent spectral features were changed depending on the proportion of Eu3+(A) and Eu3+(B), especially the PL peaks at 595 nm were intensified most in the La3+ codoped samples. Consequently, the site-dependent Eu3+ PL features in CZO and CHO were found to become more conspicuous by the effect of Ga3+ or La3+ codoping. The results also revealed that the codoped ions work not only to compensate for the charge of aliovalent Eu3+ but also to drive Eu3+ to the intentional doping sites.

DOI： 10.1021/acs.inorgchem.2c03809

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Site-Dependent Tb<sup>3+</sup>Luminescence by Energy Transfer from Ce<sup>3+</sup>in Ce<sup>3+</sup>-Tb<sup>3+</sup>Codoped LaLuO<inf>3</inf> 査読有り国際誌

Nagashima S., Ueda K., Omata T.

Journal of Physical Chemistry C 126 ( 14 ) 6499 - 6504 2022年04月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

Ce3+-Tb3+codoped LaLuO3was prepared by doping Tb3+site-selectively at a La or Lu site and doping Ce3+simultaneously at a La site. X-ray diffraction analysis revealed the expansion and contraction of the unit-cell volume according to the substituting sites of Ce3+and Tb3+, confirming the occupation of Ce3+at a La site and Tb3+at a La or Lu site. Photoluminescence due to energy transfer from Ce3+to Tb3+was investigated by exciting the 4f-5d transition band of Ce3+. The site-dependent Tb3+luminescence spectra revealed that the energy transfer occurred from Ce3+to not only Tb3+at La sites but also Tb3+at Lu sites. Because Tb3+at both sites can show green luminescence by Ce3+4f-5d excitation, as well as Tb3+4f-5d excitation, in Ce3+-Tb3+codoped LaLuO3, the excitation wavelength range for Tb3+luminescence was widely extended up to 380 nm, which is attainable with near-UV LEDs.

DOI： 10.1021/acs.jpcc.2c01074

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Energy Diagrams of Lanthanide Energy Levels in Perovskite-Type Calcium-Based Double Oxides Examined by X-Ray Photoelectron Spectroscopy 招待有り査読有り国際誌

Ueda K., Yamamoto R., Shimizu Y.

Physica Status Solidi (B) Basic Research 258 ( 12 ) 2021年12月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

The energy levels of 4f ground states for trivalent lanthanide ions (Ln3+) in CaMO3 (M=Ti, Sn, Zr, Hf) are examined using X-ray photoelectron spectroscopy (XPS). Some Ln3+ 4f energy levels referred to the valence band maximum (VBM), especially for Tb3+, are evaluated from the Ln3+ 4f states extracted by the difference XPS spectra between nondoped and Ln3+-doped materials. The energy position of the zigzag curves for the Ln3+ 4f energy levels are referred to the Tb3+ 4f energy levels obtained from the XPS measurements. Energy gaps and Ln2+ 4f energy levels are also estimated from the absorption and photoluminescence excitation spectra of nondoped and Eu3+-doped materials. On the basis of the experimental values, the energy diagrams aligned at the VBM are illustrated and compared to understand the Ln 4f energy levels in the electronic structures of the perovskite-type calcium-based double oxides.

DOI： 10.1002/pssb.202100450

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Host Lattice-Excitation-Enhanced Photoluminescence in Eu<sup>3+</sup>-Doped LaInO<inf>3</inf>Epitaxial Films 査読有り

Oshime N., Ueda K., Takashima H.

Crystal Growth and Design 21 ( 5 ) 2663 - 2667 2021年05月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

Oxide-phosphor epitaxial films having a large lattice mismatch with the substrate may significantly alter the photoluminescence (PL) properties of the bulk or powder. We investigated the PL characteristics of phosphor Eu0.10La0.90InO3 (ELIO; lattice mismatch of approximately 5-7% with SrTiO3 (STO)) epitaxially grown on an STO single crystal (001). X-ray diffraction patterns indicated that the ELIO epitaxial film on STO (001) formed a 90° domain with a size of tens of nanometers and underwent 4.62% lattice expansion. Intense orange-red luminescence was observed from the ELIO epitaxial film under ultraviolet excitation, similar to the case of the ELIO powder. The PL excitation spectra indicated that host lattice (HL) excitation, rather than charge-transfer excitation, led to the red luminescence in the ELIO epitaxial film, in contrast to that in the ELIO powder. The efficient HL excitation in the ELIO epitaxial film will be advantageous for the fabrication of thin-film-type EL devices with an ELIO emitting layer.

DOI： 10.1021/acs.cgd.0c01531

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Site-Dependent Eu<sup>3+</sup> Photoluminescence in Double Perovskite-Type Alkaline Earth Lanthanum Tantalates 査読有り

Ueda K., Yoshino T., Shimizu Y., Honma T., Massuyeau F., Jobic S.

Journal of Luminescence 229 2021年01月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

Site-dependent Eu3+ photoluminescence (PL) was examined utilizing the structural difference of two Eu3+ doped alkaline earth lanthanum tantalates with the B-site-ordered double perovskite-type structure (AA’)[BB’]O6, viz. (CaLa1−xEux)[CaTa]O6 (CLTO:Eu3+) and (Ba2)[La1−xEuxTa]O6 (BLTO:Eu3+) (x = 0.01, 0.10). The locations of the Eu3+ ions were experimentally determined by X-ray absorption near edge structure of the Eu LIII edge and confirmed to be A sites in CLTO:Eu3+ and B sites in BLTO:Eu3+ as expected from the nominal compositions. Intense charge transfer (CT) excitation bands were observed in the UV region in the PL excitation spectra of both materials. Because of the shorter bond lengths and larger electronic repulsion at B sites than A sites, the CT excitation band of Eu3+ at B sites in BLTO:Eu3+ was blue-shifted compared to that of Eu3+ at A sites in CLTO:Eu3+. By UV excitation in the CT bands, both materials showed red luminescence. However, due to the difference in the site symmetry of A and B sites, the Eu3+ emission was mainly derived from the 5D0 – 7F2 transitions in CLTO:Eu3+ and from the 5D0 – 7F1 transitions in BLTO:Eu3+ in relation with Eu3+ at A and B sites, respectively. The lifetimes of the emission were also dependent on the Eu3+ sites resulting in the longer lifetimes of Eu3+ ions at B sites than those at A sites.

DOI： 10.1016/j.jlumin.2020.117683

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希土類イオン添加ペロブスカイト型酸化物蛍光体のサイト別発光とサイト間エネルギー移動招待有り査読有り

植田和茂

セラミックス ( 日本セラミックス協会 ) 55 ( 11 ) 800 - 805 2020年11月

Site dependence of Tb<sup>3+</sup> luminescence in double perovskite-type alkaline earth lanthanum tantalates 査読有り

Ueda K., Tanaka S., Yamamoto R., Shimizu Y., Honma T., Massuyeau F., Jobic S.

Journal of Physical Chemistry C 124 ( 1 ) 854 - 860 2020年01月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

Tb3+ doped alkaline earth lanthanum tantalates with the B-site-ordered double perovskite-type structure (AA′)[BB′]O6 (namely, (CaLa1−xTbx)[CaTa]O6 (CLTO:Tb3+) and Ba2[La1−xTbxTa]O6 (BLTO:Tb3+) with x = 0.01, 0.10) were prepared, and their Tb3+ photoluminescence (PL) properties were examined and explained based on the occupied crystal sites (A or B sites). The locations of the Tb3+ activators were elucidated by analyzing powder X-ray diffraction patterns and X-ray absorption near edge structure at the Tb LIII edge. Tb3+ ions are located at A sites in CLTO:Tb3+ and at B sites in BLTO:Tb3+ as indicated in the nominal compositions. Both CLTO:Tb3+ and BLTO:Tb3+ exhibited intense PL excitation (PLE) peaks in the UV region due to the 4f−5d excitation for Tb3+. The PLE peak of Tb3+ in BLTO:Tb3+ showed a marked red-shift compared to that in CLTO:Tb3+ primarily because of the larger crystal fields at the B sites than at the A sites. The main PL peaks associated with the 4f−4f transitions from 5D4 to 7F5 states are also influenced by the crystal field, and the splitting of the PL peaks for Tb3+ at the B sites in BLTO:Tb3+ is more pronounced than that at the A sites in CLTO:Tb3+. In addition, owing to a downshift of the Tb 5d orbitals, the PL in the blue region derived from 5D3−7FJ transitions is quenched for Tb3+ in BLTO:Tb3+

DOI： 10.1021/acs.jpcc.9b09260

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九州工業大学工学部応用化学科の化学実験教育招待有り査読有り

中戸晃之, 竹中繁織, 岡内辰夫, 山村方人, 植田和茂

化学と教育 ( 公益社団法人日本化学会 ) 68 ( 3 ) 114 - 117 2020年01月

記述言語：日本語掲載種別：記事・総説・解説・論説等（学術雑誌）

<p>九州工業大学工学部応用化学科では，2年次前期より3年次後期にかけて，分析化学，物理化学，有機化学，化学工学・無機化学の順序で，学生実験を実施している。実験技術の習得に加え，エンジニアリングデザイン，コミュニケーション，チームワークなどの能力の涵養も目的としている。有機化学実験ではPBL（課題解決型学習）方式を取り入れており，学生アンケートや教員の実感では有効に機能していると考えられる。</p>

DOI： 10.20665/kakyoshi.68.3_114

その他リンク： https://ci.nii.ac.jp/naid/130007993107

Site-Selective Doping and Site-Sensitive Photoluminescence of Eu<sup>3+</sup> and Tb<sup>3+</sup> in Perovskite-Type LaLuO<inf>3</inf> 査読有り国際誌

Ueda K., Tanaka S., Yoshino T., Shimizu Y., Honma T.

Inorganic Chemistry 58 ( 16 ) 10890 - 10897 2019年08月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

© 2019 American Chemical Society. Eu3+ and Tb3+ ions were site-selectively doped into LaLuO3 with the orthorhombic perovskite-type structure (ABO3), and their luminescence properties were examined considering the doping sites (A or B sites). The X-ray diffraction analysis revealed the expansion or contraction of the unit cell volumes of the materials depending on the doping sites. The spectra of X-ray absorption near edge structure for the Eu and Tb LIII edge exhibited different shapes for the ions at A and B sites, confirming the site-selective doping of Eu3+ and Tb3+ in LaLuO3. The photoluminescence (PL) and PL excitation (PLE) spectra of the materials also showed some differences caused by the doping sites. The intensities of the Eu3+ PL peaks derived from the 5D0-7F1 transitions and those from the 5D0-7F2 transitions were markedly different between Eu3+ at A sites and those at B sites because of the different site symmetries. The splitting of the intense Tb3+ PL peaks originating from the 5D4-7F5 transitions and the absence of PL peaks from 5D3-7FJ transitions were found only for Tb3+ at B sites because of the strong crystal field at B sites. In addition to the PL spectra, the positions of PLE peaks originating from charge transfer transitions in Eu3+ and the 4f-5d transitions in Tb3+ depended on the doping sites. The successful site-selective doping enabled us to clarify the site-sensitive luminescence properties of Eu3+ and Tb3+ doped in the perovskite-type LaLuO3.

DOI： 10.1021/acs.inorgchem.9b01273

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Ultraviolet emission from YAlO<inf>3</inf>:Gd<sup>3+</sup> thin film electroluminescent devices fabricated on perovskite-type oxide substrates 査読有り国際誌

Shimizu Y., Ueda K.

Optical Materials 91 371 - 375 2019年05月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

© 2019 Elsevier B.V. Inorganic ultraviolet-electroluminescent (UV-EL) devices with a Gd3+-doped YAlO3 thin film emitting layer were fabricated by radio frequency sputtering. Three kinds of perovskite-type oxide substrates, namely a SrTiO3 single crystal (STO-SC), BaTiO3 single crystal (BTO-SC), and BaTiO3 polycrystalline disk (BTO-PC), were used for the devices. The influence of the substrates on the UV-EL properties of YAlO3:Gd3+ was investigated. It was found that EL threshold voltage, emitting locations, and EL intensity have changed depending on the substrates. The UV-EL attributed to the 6PJ-8S7/2 transitions in Gd3+ was observed in the BTO-PC substrate device with applied voltage of approximately over 200 V and in the STO-SC and BTO-SC substrate devices with that of approximately over 500 V. The STO-SC and BTO-SC devices showed EL only near the edges of a back electrode, whereas the BTO-PC device showed surface EL over the whole electrode. It was considered the local EL at the electrode edges in the SC substrate devices was caused by a concentrated electric field in the vicinity of the electrodes. The BTO-PC device showed not only the lowest EL threshold voltage but also the most intense EL in the three devices. Because the BTO-PC substrate has a high dielectric constant and appropriate surface roughness, which results in a high and uniform electric field over the back electrode, the YAlO3:Gd3+ emitting layer showed intense surface UV-EL with lower applied voltage.

DOI： 10.1016/j.optmat.2019.03.047

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Ln <sup>3+</sup> 4f Energy Levels in CaTiO <inf>3</inf> Analyzed by XPS Measurements 査読有り国際誌

Yamamoto R., Ueda K.

Physica Status Solidi (A) Applications and Materials Science 216 ( 5 ) 1700776(1) - 1700776(5) 2019年03月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim The energy levels of Ln 3+ 4f ground states in CaTiO 3 are analyzed using X-ray photoelectron spectroscopy (XPS). The Ln 4f states in the XPS spectra are extracted utilizing large photoionization cross section differences between Ln 4f and O 2p states. The Ln 3+ 4f energy levels referred to the valence band maximum are evaluated to be 0.8 eV for Pr 3+ , −5.0 eV for Gd 3+ , 0.9 eV for Tb 3+ , and −4.6 eV for Lu 3+ from the extracted XPS spectra. Although the obtained values of Gd 3+ and Lu 3+ 4f levels are deeper in the valence band, the values of Pr 3+ and Tb 3+ 4f levels are in good agreement with those reported previously. The difference in the photoluminescence colors between Pr 3+ -doped CaTiO 3 and CaZrO 3 is simply explained from the Pr 3+ 4f energy levels located in the bandgaps.

DOI： 10.1002/pssa.201700776

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Luminescence and Location of Gd<sup>3+</sup>or Tb<sup>3+</sup>Ions in Perovskite-Type LaScO<inf>3</inf> 査読有り国際誌

Ueda K., Aoki T., Shimizu Y., Massuyeau F., Jobic S.

Inorganic Chemistry 57 ( 15 ) 8718 - 8721 2018年08月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

© 2018 American Chemical Society. The luminescence properties of Gd3+or Tb3+ions at La and Sc sites were investigated in LaScO3with a distorted perovskite-type structure (ABO3). Although the luminescence of lanthanide ions located at B sites is not common and has not been examined in detail, Gd3+or Tb3+luminescence from B sites and A sites is clearly observed in Gd3+- or Tb3+-doped LaScO3. The differences in the luminescence characteristics concern peak positions, peak shapes, and decay time, which are all influenced by the crystal field and the site symmetry. The UV luminescence of Gd3+at B sites shows a red shift compared to Gd3+at A sites, and the green luminescence of Tb3+at B sites contrasts with the blue-violet and green luminescence of Tb3+at A sites. The decay time of the luminescence from B sites is systematically longer than that from A sites in both the Gd3+and Tb3+cases.

DOI： 10.1021/acs.inorgchem.8b01288

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照明の化学2 招待有り査読有り

植田和茂

化学と教育 ( 公益社団法人日本化学会 ) 65 ( 11 ) 578 - 581 2017年11月

担当区分：筆頭著者,　最終著者,　責任著者記述言語：日本語掲載種別：記事・総説・解説・論説等（学術雑誌）

<p>炎色反応といえばいくつかの元素とその色の対応をすぐに思い出されるかもしれないが，天井の蛍光灯を見ても同じように元素とその発光色の対応をすぐに想像できないと思われる。蛍光灯ではいくつかの色を混ぜて白色にしているため，想像できないのも当然であるが，原子からの固有の発光を見ているという点では炎色反応の発色も蛍光灯も同じことである。放電ランプでは放電管中の気体の原子やイオンからの発光を利用し，蛍光灯やLED照明では蛍光体中に添加された微量の陽イオンからの発光を利用している。ここでは，照明として身近に使われる放電ランプ，蛍光灯，LED照明の仕組みと進歩について簡単に解説する。</p>

DOI： 10.20665/kakyoshi.65.11_578

Photo- and cathodoluminescence of Eu<sup>3+</sup>or Tb<sup>3+</sup>doped CaZrO<inf>3</inf>films prepared by pulsed laser deposition 査読有り国際誌

Ueda K., Shimizu Y., Takashima H., Massuyeau F., Jobic S.

Optical Materials 73 504 - 508 2017年11月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

© 2017 Elsevier B.V. Luminescent films of Eu 3+ or Tb 3+ doped CaZrO 3 were epitaxially grown on SrTiO 3 or LaAlO 3 (001) single crystal substrates by pulsed laser deposition (PLD). They showed a high transmittance in the visible region and a smooth surface. Uniform red photoluminescence (PL) was observed from Eu 3+ 5% doped films, and blue and green PL was observed from Tb 3+ 0.5% and 5% doped films, respectively. These PL spectra of the films turned out to be very similar to those of the powder samples. Practically, it has to be noticed the use of a LaAlO 3 substrate is necessary for intense blue luminescence for Tb 3+ 0.5% doped films to avoid optical absorption of emitted light by the SrTiO 3 substrate. The cathodoluminescence (CL) spectra of the red and green luminescent films were almost the same as those PL spectra. In contrast, blue CL was significantly enhanced in CL compared to PL. This was attributed to the shorter lifetime of the 5 D 3 - 7 F J transitions and many excited electron-hole pairs, which were generated rapidly on high energy electron irradiation.

DOI： 10.1016/j.optmat.2017.09.007

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Luminescence and Valence of Tb Ions in Alkaline Earth Stannates and Zirconates Examined by X-ray Absorption Fine Structures 査読有り国際誌

Ueda K., Shimizu Y., Nagamizu K., Matsuo M., Honma T.

Inorganic Chemistry 56 ( 20 ) 12625 - 12630 2017年10月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

© 2017 American Chemical Society. The difference in Tb 3+ green luminescence intensities in doped perovskite(ABO 3 )-type alkaline earth stannates, AeSnO 3 (Ae = Ca, Sr, Ba), and the Mg codoping effect on the luminescence intensities in doped CaMO 3 (M = Sn, Zr) were investigated utilizing the X-ray absorption fine structures (XAFS) of the Tb L III absorption edge. It is considered that the local symmetry at A sites is responsible for the different Tb 3+ luminescence intensities in AeSnO 3 (Ae = Ca, Sr, Ba) doped with Tb ions at A sites. However, it was found from the XAFS spectra that some Tb ions are unintentionally stabilized at B sites as Tb 4+ , especially in BaSnO 3 . Not only the central symmetry for Tb 3+ at A sites but also the presence of Tb 4+ at B sites were considered to bring about the absence of Tb 3+ luminescence in doped cubic BaSnO 3 . No obvious changes in the Tb 3+ local structure at A sites were detected between Tb single doped and Tb-Mg codoped CaMO 3 (M = Sn, Zr) from the extended XAFS oscillation, but the trace of Tb 4+ at B sites in the Tb single doped sample was observed in the X-ray absorption near edge structures. It is, therefore, considered that the Tb 3+ luminescence enhancement by Mg codoping is primarily attributed to the charge compensation rather than the changes in the local structure around Tb 3+ at A sites.

DOI： 10.1021/acs.inorgchem.7b02165

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Thermoelectric properties and figure of merit of perovskite-type Sr1-xLaxSnO3 ceramics 査読有り国際誌

Masahiro Yasukawa, Kazushige Ueda, Satoru Fujitsu, Hideo Hosono

Ceramics International 43 ( 13 ) 9653 - 5657 2017年04月

記述言語：英語掲載種別：研究論文（学術雑誌）

The thermoelectric properties of perovskite-type Sr1−xLaxSnO3 ceramics with x=0.01–0.05 were evaluated from the Seebeck coefficient S, electrical conductivity σ, and thermal conductivity κ measured at high temperatures. The La-doped ceramics were n-type semiconductors exhibiting thermally activated electrical conduction behaviors in the temperature range of 473–1073 K. Eelectron carriers were introduced into the conduction band from doped La atoms up to x=0.03, which was the solubility limit of La at Sr site. The temperature dependence of the κ values for the ceramics was unaffected by both the La content and the microstructures. Estimations of the electronic thermal conductivities by the Wiedemann-Franz law revealed that the phonon thermal conductivities were dominant for all ceramics. The dimensionless figure of merit ZT increased with increasing temperature for all ceramics and reached 0.02–0.05 at 1073 K. In contrast to cubic Ba1−xLaxSnO3 ceramics, bending of the Sn–O–Sn bonds due to octahedral tilting distortion in Sr1−xLaxSnO3 lowered the electron mobility, decreasing the power factor S2σ and ZT values, although it effectively reduced the phonon mean free path, decreasing the κ values.

DOI： 10.1016/j.ceramint.2017.04.136

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Photoluminescence excitation spectra of lanthanide doped YAlO<inf>3</inf> in vacuum ultraviolet region 査読有り国際誌

Shimizu Y., Ueda K., Inaguma Y.

Optical Materials 66 327 - 331 2017年04月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

© 2017 Elsevier B.V.To understand luminescent mechanisms of lanthanide (Ln) doped phosphors, it is important to know the energy positions of unoccupied Ln2+ 4f and Ln3+ 5d states, as well as occupied Ln3+ 4f states, relative to the energy bands of host materials. Photoluminescence excitation (PLE) spectra of Ln doped YAlO3 were measured in a vacuum ultraviolet (VUV) region and the energy positions of Ln2+ 4f and Ln3+ 5d states in the wide-gap YAlO3 were elucidated. Peaks assignable to host lattice excitation were observed in all samples at approximately 8 eV in the PLE spectra. PLE peaks derived from charge transfer (CT) and 4f-5d transitions were observed at lower energy than the bandgap energy. Ln2+ 4f energy levels were obtained from the PLE peak energies for the CT transitions along with the valence band maximum. In contrast, Ln3+ 5d energy levels were evaluated from those for the 4f-5d transitions along with the Ln3+ 4f energy levels, which were obtained previously from X-ray photoelectron spectroscopy measurements. The elucidated Ln2+ 4f and Ln3+ 5d energy levels were exhibited in an energy diagram together with Ln3+ 4f energy levels and host energy bands. The experimental Ln2+ 4f and Ln3+ 5d energy levels were in good agreement with the reported theoretical data.

DOI： 10.1016/j.optmat.2017.02.029

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