Element-specific channels in photo-excitation of V-doped TiO₂ nanoparticles

Abstract

Refined X-ray spectroscopies can be crucial in elucidating charge transfer phenomena which play a key-role in photo-catalysis and other processes relevant for clean energy production. A deep understanding of electron photo-dynamics is, in fact, essential to develop efficient knowledge-based devices. We developed a differential illumination RIXS and HERFD-XAS [1], method on ID26 @ ESRF to investigate charge transfer phenomena with chemical sensitivity; specifically, we studied Vdoped TiO2 nanoparticles, a promising materials system for photo-catalysis, performing measurements around both the V Kα and Ti Kβ emissions. We found that visible light absorption induces the transfer of electrons from the V dopants to the host matrix cations in defective sites. With a steady state model, it was also possible to estimate the lifetime of the excited state. The value we obtained (around 1 ms) suggests that dopant-injected electrons can remain trapped near Ti atoms for a very long time. The procedure we used is completely general and can be successfully applied to detect any kind of long-living charge transfer phenomena in a wide range of possible devices [2].

Tunable Nonthermal Distribution of Hot Electrons in a Semiconductor Injected from a Plasmonic Gold Nanostructure

“…The measured results of photoexcited charge transfer from the gold nanoparticle to TiO 2 are further supported by previous X-ray studies at the Ti K-edge. − Differences in the measured photoexcited effects occur due to the nature of the X-ray transition and the carrier densities used. As discussed previously, the carrier density here is at least 1000 times less than in these reports, so edge-shift effects are not observed.…”

“…First, the transferred charge can create a shift in the X-ray peak energy. In general, the renormalization of a semiconductor band gap or the core–hole exciton energy goes as the cubed root of the carrier density. , For TiO 2 , a shift of <1 eV was measured for an excitation density of >10 W/cm 2 at the Ti K edge. − Here, the lower-power, broad-band Xe lamp leads to an excitation density of ∼10 mW/cm 2 . The Ti L edge is also measured instead of the Ti K edge.…”

Ultrafast Charge Carrier Dynamics in Vanadium-Modified TiO2 Thin Films and Its Relation to Their Photoelectrocatalytic Efficiency for Water Splitting

“…In this work, we concentrate on extending light absorption of TiO 2 thin films into the visible range via vanadium incorporation (referred to as V–TiO 2 in the following). Previously, − we used vanadium as a dopant in TiO 2 nanoparticles deposited by inert gas condensation. We found the incorporation site of vanadium to be substitutional to titanium, with both 4+ and 5+ oxidation states; V-incorporation induces the creation of intragap localized donor levels, which lead to a red shift of optical absorption, also in agreement with a recent computational work by Zhou et al The nanoparticles were deposited on a conductive substrate to obtain nanostructured and porous photoanodes used in a photoelectrochemical cell (PEC) for water splitting or were suspended in a solution for photocatalytic conversion of organic compounds.…”