Paper NM-WeP1
Facile Preparation of (NH₄)₂SiF₆ Particles with High Fluorescence Quantum Yield

Wednesday, December 10, 2014, 4:00 pm, Room Mauka

Fluorescence materials are used for a broad range of industry and biomedical technology applications involving electroluminescent displays and fluorescent contrast dye of bioimaging. However, they are confronting some serious problems, such as complicated preparation techniques and low production yield. Therefore, it is necessary to develop new synthesis approaches for realization of facile preparation and large-scale production of fluorescence materials. We have prepared ammonium hexafluorosilicate ((NH₄)₂SiF₆) particles as one of the fluorescence materials using a chemical route with good productivity. These (NH₄)₂SiF₆ particles possess excellent advantages such as high-efficiency fluorescence and long-term photostability compared to the other silicon (Si)-based fluorescence materials. In this presentation, we propose a new way to fabricate (NH₄)₂SiF₆ particles by simplified procedures based on a chemical approach. The features of our synthesis technologies are to adopt the simplified synthesis system in which only Si powders and chemicals consisting of nitric hydrofluoric acid solution were hermetically sealed in polymeric container without any vacuum systems. The (NH₄)₂SiF₆ particles with mean diameter of approximately 700 nm were densely deposited on the Si substrate by using this novel synthesis system. The crystalline structures and the chemical compositions of (NH₄)₂SiF₆ particles were confirmed by X-ray diffraction (XRD) patterns and Fourier transform infrared (FTIR) spectroscopy. The XRD patterns were consistent with the sharp diffraction peaks derived from the cubic phase of crystalline (NH₄)₂SiF₆ with space group of Fm3m(225). For the FTIR characterization, the absorption peaks related to the SiF₆^2- and NH₄+ ions in addition to N-H mode were also observed. These results demonstrate that the (NH₄)₂SiF₆ particles are not only maintained high crystallinity but also composed of ammonium and silicon fluoride as major ingredients. Such (NH₄)₂SiF₆ particles exhibited bright reddish orange fluorescence with a peak wavelength at 630 nm under the irradiation of xenon lamp equipped with optical bandpass filter of 365 nm. The main advantages of (NH₄)₂SiF₆ particles are to attain the high fluorescence quantum yield of 34 %. Additionally, the fluorescence intensity was maintained about 80% of the initial maximum intensity even after aging beyond six months. Therefore, our suggested synthesis technologies can provide a new chemical route for the fabrication of high-brightness and stable fluorescence particles.