Solid-state electro-active photonic crystals based on Tantalum-doped Titanium Dioxide multilayers

Photonic crystals can manipulate light by impeding transmission through photonic band gaps (PBGs), unlocking vivid structural colors and beating conventional spectrally-selective pigments. Nowadays, research is targeting at active and electrically-driven devices, moving beyond stacks of inert dielectrics. Plasmonic Transparent Conductive Oxides (TCOs) become appealing owned to their adjustable charge carrier density upon external stimuli (electrical biases), that enable electro-active control even in complex photonic architectures. Here, pioneer compact/porous one-dimensional PC multilayers, completely solid and entirely based on the novel and earth-abundant Tantalum-doped Titanium Dioxide TCO (Ta:TiO 2 ), have been developed with pulsed laser deposition through an original one-step method, by mastering the oxygen supply at deposition. Engineered doping and geometry enable tunable PBGs in the visible range. Electro-doping achieves PBG blue-shifts of 11-16 nm under low bias (≤7 V) without liquid electrolytes. These findings unveil the potential of actively-tunable Ta:TiO 2 PCs to foster technological advancements in electro-optic switches, biosensors and anticounterfeit devices. • One-step original fabrication of active-tunable photonic crystals with Ta:TiO 2 TCO • Blue-shift of photonic band gaps (up to 16 nm) achieved with low voltages (≤7 V) • Multilayers with 10% at. Ta and optimized geometry show maximum optical tunability • Modulation mechanism related to the inherent carrier density tunability of the TCO • Multifunctional devices operating in VIS-IR for sensing, anticounterfeiting