Nb, Ta and Hf-The tri-dopant tournament for the enhancement of TiO2 photochromism

TiO2 quantum dot (QD) size nanoparticle colloids have shown tremendous photochromic response. Here we show that the of the photochromic response of TiO2 QDs can be further enhanced by doping. Our synthesis approach allows to reach high nominal doping level by substituting up to 20 % of Ti in TiO2 without phase segregation simultaneously keeping particles in ultra-small. We compare the effect of different dopants (Nb5+, Hf4+ and Ta5+) on photochromic properties of TiO2 QDs. We show all dopants in study enhance the response kinetics and total transmittance change. From all three dopants, Nb5+ provides strongest response and fastest coloration while Hf4+ doped TiO2 QDs exhibit fastest recovery when the UV light is off. The presented insight in photochromic properties of doped TiO2 QDs will allow to develop photochromic devices and materials with better performance.