Strong, Rapid, and Reversible Photochromic Response of Nb Doped TiO₂ Nanocrystal Colloids in Hole Scavenging Media

Abstract

Understanding photochromicity is essential for developing new means of modulating the optical properties and optical response of materials. Here, we report on the synthesis and exciting new photochromic behavior of Nb5+ doped TiO2 nanoparticle colloids (NCs). We find that, in hole scavenging media, Nb5+ doping significantly improves the photochromic response time of TiO2 nanoparticles. In the infrared regime, Nb-doped TiO2 NCs exhibit 1 order of magnitude faster photoresponse kinetics than the pristine TiO2. Enhanced photochromic response is observed in the visible light regime as well. The transmittance of Nb-doped TiO2 NCs drops to 10% in less than 2 min when irradiated by UV-light in the 500 nm range. The photochromic reaction is fully reversible. The physical origin of the high reaction rate is the high Nb5+ concentration. As a donor dopant, Nb5+ builds up a significant positive charge in the material, which leads to highly efficient electron accumulation during the UV irradiation and results in a rapid photoresponse. EPR experiments identify a new defect type from Nb5+ doping, which alters the physical mechanisms available for transmittance modulation. Our new NCs are economic to synthesize and highly suitable for switchable photochromic applications, e.g., smart windows for modulating visible light and infrared transmittance in built-environments.

Photodoping-Inspired Room-Temperature Gas Sensing by Anatase TiO2 Quantum Dots

“…The concept is inspired from photodoping of ultrasmall (quantum dot size) TiO 2 nanoparticles in hole scavenging media, where photogenerated holes are scavenged via photochemical oxidation of the alcohol while electrons populate the conduction band. , This, in turn, alter the electrical and optical properties of the TiO 2 nanoparticles. In the present case, we use the photodoping concept for detecting ethanol at room temperature in the presence of humidity.…”

Photochromic TiO2/PEGDA organogels

“…For the full TiO 2 QD synthesis procedure, reader is advised to see our previous publication [15]. Briefly, titanium tetra n-butoxide was added to a solution of acetylacetone in n-butanol.…”

“…However, carbonyl groups are very mild hole scavengers at best; thus, the hole scavenging in the present photochromic gels is mainly done by either DMF or ethanol [37]. The introduction of Ti 3+ and oxygen vacancies leads to absorption in the visible light range, while the accumulated electrons are responsible for NIR light absorption due to surface plasmon resonance [15]. All these result in a decrease in transmittance, leading to (1)…”

“…Anatase TiO 2 is most attractive photochromic material among other TMOs material due to non-toxicity, elemental abundancy and strong photoresponse [10]. The photochromic response of anatase TiO 2 can be modified either by changing the hole scavenger [14] or doping [15]. Strong photochromic response from TiO 2 has been demonstrated mainly for colloids so far.…”

Carbon Nitride Nanosheet-Based Photochromic Physical Unclonable Functions for Anticounterfeiting Applications

“…Since the concept of PUFs was first proposed by Pappu et al in 2002, various optical responses (e.g., reflection, scatterings, − diffraction, luminescence, − and a mixture of these optical responses − ) used in conventional anticounterfeiting labels have also been applied to the PUF anticounterfeiting field. Although photochromic phenomena have been widely discovered, − as far as we know, photochromic PUFs have not been reported. In addition, developing new optical PUFs through a low-cost manufacturing process has practical applications in the anticounterfeiting field.…”