New transparent flexible nanopaper as ultraviolet filter based on red emissive Eu(III) nanofibrillated cellulose

A new kind of highly red emissive and transparent nanopapers as ultraviolet filter are produced from lanthanide complex Eu(TTA)(3)(H2O)(2) grafted nanofibrillated cellulose (NFC) by a filtration process using a Buchner funnel. The nanopapers Eu-NFC 14 with different thickness (0.023 mm, 1; 0.04 mm, 2; 0.081 mm, 3 and 0.1 mm, 4) possess a fibres with dimensions of approximately 50 nm in diameter and several micrometres in length. Those nanopapers exhibit excellent ultraviolet A (UVA; 320400 nm) filter property and high optical transmittance (>73% at wavelength of 600 nm). The presence of Eu(TTA)(3)(H2O)(2) in Eu-NFC nanopapers can block 97% UVA (at 348 nm) light and convert it into pure red emission (CIE: x = 0.663, y = 0.333) through the efficient triplet-triplet energy transfer process. The efficient red emission can significantly improve the photo-stability of beta-diketones type UVA filter. It can sustain for 10 h without decomposition under UV irradiation at 365 nm, which makes it possible to be applied in UVA filters. Moreover, its low coefficient of thermal expansion (CTE: 6.39 ppm K-1 of nanocellulose), is superior to petroleum-based materials for red organic light-emitting devices. (C) 2017 Elsevier Ltd. All rights reserved.