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Electrophoretic Deposition and Characterization of Transparent Nanocomposite Films of YVO4:Bi3+,Eu3+ Nanophosphor and Silicone-Modified Acrylic Resin

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journal contribution
posted on 11.02.2014, 00:00 by Yoshiki Iso, Satoru Takeshita, Tetsuhiko Isobe
We fabricated nanocomposite films from an aqueous suspension of red-emitting YVO4:Bi3+,Eu3+ nanoparticles (hydrodynamic size: 22 ± 6 nm) and silicone-modified acrylic resin nanoparticles of (60 ± 15 nm) by electrophoretic deposition under application of a constant voltage. The nanocomposite films were formed from these negatively charged nanoparticles on ITO-coated glass substrates on the anodic side at the volume ratio of nanophosphor:resin ∼ 40:60. According to transmission electron microscopy observations, the YVO4:Bi3+,Eu3+ nanoparticles are well-dispersed around the resin nanoparticles. The fabricated films are transparent to the naked eye under white light because both nanoparticles show no absorption and low light scattering in the visible region. A silicone-modified acrylic resin film without the nanophosphor exhibits no absorption in the UV region (>300.0 nm). However, the fabricated nanocomposite films show near-UV absorption owing to the interband transition between the valence band and the conduction band of the YVO4:Bi3+,Eu3+ nanoparticles. A sharp emission peak corresponding to the 5D07F2 transition of Eu3+ is observed at 619.5 nm, under 365.0 nm excitation, for each nanocomposite film. The photoluminescence intensity at 619.5 nm under 365.0 nm excitation is proportional to 1–10–OD (OD: optical density at 365.0 nm) for film thicknesses ≤6 μm. This is attributed to the low light scattering from both nanoparticles in the nanocomposite film. Conversely, the observed photoluminescence intensity for film thicknesses >6 μm is higher than the value expected from the proportional relationship. This suggests that the excitation of the nanophosphors efficiently occurs due to multiple scattering of excitation light.