| Synthesis and luminescence property of Li1.11Ta0.89Ti0.11O3: Eu3+, Sm3+ red phosphor |
| Prof. Hiromi Nakano |
| Toyohashi University of Technology |
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| The ternary Li2O-Ta2O5-TiO2 system compounds have been applied to the host materials of new phosphors [1]. The RE (=Eu3+, Sm3+, Er3+, Dy3+ or Tm3+) doped Li1+xTa1-xTixO3 (LTT, 0 < x < 0.25) phosphors, showing various emission colors, have been synthesized to compared their PL properties to those of the LNT phosphors [2]. In the LTT host materials, the most effective activator was Eu3+. The internal quantum efficiency attained the value of over 84 % for the host composition of Li1.11Ta0.89Ti0.11O3 (x = 0.11) [2]. In this work, we have tried to enhance the emission intensities of the LTT phosphors by co-doping of Eu3+ and Sm3+ because the Sm3+ ions have been reported to act as sensitizers for various types of Eu-doped phosphors [3]. The starting powders were mixed and pressed in air at 1423 K for 15 h in a conventional electric furnace. Characterizations were carried out by X-ray diffraction (XRD) and a scanning electron microscope. Excitation and emission spectra of the obtained samples were measured by a spectrometer (model FP-6500, JASCO). Quantum efficiency was measured by a spectral radiometer (MCPD-7000, Otsuka Electronics Co. LTD.,) In order to clarify the effect of Sm3+-ion doping on the photoluminescence properties, the Sm2O3 content was varied from 0 to 0.25 wt%, with a fixed Eu2O3 concentration of 2.5 wt%. We determined the internal quantum efficiency (Fig. 1). The results show that the co-doped phosphor with Sm2O3 at 0.1wt% showed the highest PL intensity, with the internal quantum efficiency being 98 %. The PL intensity of this phosphor, doped with Eu2O3 at 0.25 wt% and Sm2O3 at 0.1 %, was ca. 1.4 times higher than that of the 0.25 wt% Eu3+-doped Li1.11Ta0.89Ti0.11O3 phosphor, indicating that the small amount of Sm3+ acted as an effective sensitizer. The external quantum efficiency was slightly improved up to ca. 20%, although the improvement degree was still unsatisfactorily low, which must be caused by the low absorptivity due to the forbidden 4f-4f transition of the Eu3+ ion. No emission peak of the co-doped phosphor was observed at around 607 and 650 nm by the transition of the Sm3+ ion. The Sm3+ transfers energy to the 5DJ state of Eu3+ without any red-light emission. Hence, the highly efficient red-light emission due to Eu3+ would occur through the 5D0-7FJ transition, without the emission due to Sm3+. References: [1] H. Nakano, K. Ozono, H. Hayashi, S. Fujihara, J. Am. Ceram. Soc. 95(9) (2012) 2795. [2]H. Nakano, S. Suehiro, S. Furuya, H. Hayashi, S. Fujihara, Mater. 6 (2013) 2768. [3] G.-H. Lee, T.-H. Kim, C. Yoon, S. Kang, J. Lumin. 128 (2008) 1922 -1926. |
| Acknowledgements : This work (H. N.) was partially supported by a Grant-in-Aid for Scientific Research (c) No. 25420709 by the Japan Society for the Promotion of Science. |
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