Low Temperature Synthesis of Halide Phosphors Using Novel Water-Assisted Solid-State Reaction Method

In recent years, nano-phosphor materials have attracted much attention due to their significant potential for high-performance micro-LED displays and solid state lighting devices. In addition, nano-phosphors are considered to be promising candidates for spectral-converters to enhance the energy-conversion efficiency of silicon solar cells. Synthesis of nano-phosphors can be categorized in two ways namely, chemical and physical methods. Various methods such as the sol-gel, hydro-thermal, or the polymerized complex methods are usually used to synthesize nano-phosphor materials. However, these methods require expensive and special experimental equipment, raw materials, or solvents. In this study, we synthesized nano-sized halide phosphors using a novel water-assisted solid-state reaction (WASSR) method. This novel soft chemical synthesis method is very simple and can synthesize nano-particle materials just by storing or mixing raw materials added a small amount (typically 10wt%) of water in a reactor at low temperature below 500 K. Typical particle sizes (under 100 nm) of the samples prepared by the WASSR method were smaller than that (2 - 10 micrometer size) of the sample prepared by the conventional solid-state reaction method. For example, a stoichiometric mixture of CsCl, CaCl 2 and EuCl 3 hydrate was mixed for the WASSR synthesis of CsCaCl 3 :Eu 2+ phosphor. Then, a small amount (2 wt%) of water was added to the mixture and mixed using mortar for 1 min to synthesize a single phase of CsCaCl 3 :Eu 3+ . For the reduction of Eu 3+ ion, 6 wt % of hydrazine monohydrate was added to the CsCaCl 3 :Eu 3+ and heated in the closed reactor for 12 h at 493 K. The XRD pattern of the products are in good agreement with that of single phase CsCaCl 3 . The SEM image and the photoluminescence spectra of CsCaCl 3 :Eu 2+ is shown in Figure. CsCa 0.09 Eu 0.01 Cl 3 shows strong blue emission under the excitation of UV light. Our proposed low cost and low-temperature synthesis technique are promising for an industrial application for phosphor materials synthesis processing. Acknowledgment This research was financially supported by the Ministry of Trade, Industry and Energy(MOTIE) and Korea Institute for Advancement of Technology(KIAT) through the International Cooperative R&D program (P0006844_Development of color conversion nanocrystal luminescence materials for next generation display). References [1] T. Kaneko, S. W. Kim, A. Toda, K. Uematsu, T. Ishigaki, K. Toda, M. Sato, J. Koide, M. Toda, Y. Kudo, T. Masaki, and D. H. Yoon, Sci. Adv. Mater., 7, 1502 (2015). [2] S-W. Kim, T. Hasegawa, M. Watanabe, M. Muto, T. Terashima, Y. Abe, T. Kaneko, A. Toda, T. Ishigaki, K. Uematsu, K. Toda, M. Sato, E. Kawakami, J. Koide, M. Toda, Y. Kudo, T. Masaki and D. H. Yoon, Appl. Spect. Rev., 52, 1 (2017). Figure 1