EDTA-assisted phase conversion synthesis of (Gd0.95RE0.05)PO4 nanowires (RE = Eu, Tb) and investigation of photoluminescence

Zhihao Wang; Ji-Guang Li; Qi Zhu; Zhengrong Ai; Xiaodong Li; Xudong Sun; Byung-Nam Kim; Yoshio Sakka

doi:10.1080/14686996.2017.1338495

EDTA-assisted phase conversion synthesis of (Gd_0.95RE_0.05)PO₄ nanowires (RE = Eu, Tb) and investigation of photoluminescence

Sci Technol Adv Mater. 2017 Jun 28;18(1):447-457. doi: 10.1080/14686996.2017.1338495. eCollection 2017.

Authors

Zhihao Wang^{1

2

3}, Ji-Guang Li^{1

2

3}, Qi Zhu^{1

2}, Zhengrong Ai¹, Xiaodong Li^{1

2}, Xudong Sun^{1

2

4}, Byung-Nam Kim³, Yoshio Sakka³

Affiliations

¹ Key Laboratory for Anisotropy and Texture of Materials, Northeastern University, Shenyang, China.
² Institute for Ceramics and Powder Metallurgy, School of Materials Science and Engineering, Northeastern University, Shenyang, China.
³ Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Japan.
⁴ School of Environmental and Chemical Engineering, Dalian University, Dalian, China.

Abstract

Hexagonal (Gd_0.95RE_0.05)PO₄·nH₂O nanowires ~300 nm in length and ~10 nm in diameter have been converted from (Gd_0.95RE_0.05)₂(OH)₅NO₃·nH₂O nanosheets (RE = Eu, Tb) in the presence of monoammonium phosphate (NH₄H₂PO₄) and ethylene diamine tetraacetic acid (EDTA). They were characterized by X-ray diffraction, thermogravimetry, electron microscopy, and Fourier transform infrared and photoluminescence spectroscopies. It is shown that EDTA played an essential role in the morphology development of the nanowires. The hydrothermal products obtained up to 180 °C are of a pure hexagonal phase, while monoclinic phosphate evolved as an impurity at 200 °C. The nanowires undergo hexagonal→monoclinic phase transformation upon calcination at ≥600 °C to yield a pure monoclinic phase at ~900 °C. The effects of calcination on morphology, excitation/emission, and fluorescence decay kinetics were investigated in detail with (Gd_0.95Eu_0.05)PO₄ as example. The abnormally strong ⁵D₀→⁷F₄ electric dipole Eu³⁺ emission in the hexagonal phosphates was ascribed to site distortion. The process of energy migration was also discussed for the optically active Gd³⁺ and Eu³⁺/Tb³⁺ ions.

Keywords: 105 Low-Dimension (1D/2D) materials; 40 Optical, magnetic and electronic device materials; 505 Optical / Molecular spectroscopy; EDTA; GdPO4; Phase conversion; nanowires; photoluminescence.