Reversible Photodoping of TiO2 Nanoparticles for Photochromic Applications

Urmas Joost, Andris Šutka, Marek Oja, Krisjanis Smits, Nicola Döbelin, Ardi Loot, Martin Jarveku,  Mika Hirsimaki, Mika Valden, and Ergo Nõmmiste

Observations on the strong photochromic effect of crystalline
TiO2 quantum dots (mean size ≈ 4 nm) are presented. The synthesized
quantum dots consist of irregularly shaped anatase TiO2 nanoparticles (NPs)
and are dispersed in butanol (8% by mass). Obtained NPs exhibit a dramatic
photoresponse to UV light, enabling effective transmittance modulation in a
broad wavelength range extending from the visible to near-infrared region, and
even the thermal black body radiation regime beyond 10 μm. The exceptional
photoresponse is attributed to hole-scavenging by butanol, TiO2 self-reduction,
injection of electrons to the conduction band, and consequent localized surface
plasmon resonances in NPs. The observed optical effect is reversible, and the
initial high transmittance state can be restored simply by exposing the NPs to
air. The applied NP synthesis route is economic and can be easily scaled for
applications such as smart window technologies

Published in Chemistry of Materials

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