Ultrafast Carrier Trapping of a Metal-Doped Titanium Dioxide Semiconductor Revealed by Femtosecond Transient Absorption Spectroscopy

Sun, Jingya; Yang, Yang; Khan, Jafar Iqbal; Alarousu, Erkki; Zhong, Guo; Zhang, Xixiang; Zhang, Qiang; Mohammed, Omar F.

doi:10.1021/am5026159

Cited by 39 publications

(49 citation statements)

References 42 publications

(87 reference statements)

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“…Ultrafast spectroscopy was also applied to track photoexcited charge carriers in doped TiO2 [37][38][39][40][41][42]. Ikeda et al observed a second-order kinetics due to electron-hole recombination, the rate constant of which increases with increasing dopant concentration [42].…”

Section: Introductionmentioning

confidence: 99%

Charge carrier dynamics and visible light photocatalysis in vanadium-doped TiO2 nanoparticles

Rossi

Pasquini

Catone

et al. 2018

Applied Catalysis B: Environmental

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Vanadium-doped TiO2 nanoparticles (V-TiO2 NPs) with a V/Ti ratio of 3.0 at. % were prepared by gas-phase condensation and subsequent oxidation at elevated temperature. Both photocatalytic activity for -NO2 reduction and photoelectrochemical water splitting were induced by V-doping in the visible spectral range > 450 nm, where undoped TiO2 NPs are completely inactive. The photocatalytic properties were correlated with the ultrafast dynamics of the photoexcited charge carriers studied by femtosecond transient absorption (TA) spectroscopy with three different excitation wavelengths, i.e. e = 330, 400, and 530 nm. Only in V-doped NPs, the photoexcitation of electrons into the conduction band by sub-bandgap irradiation (e = 530 nm) was detected by TA spectroscopy. This observation was associated with electronic transitions from an intra-gap level localized on V 4+ cations. The photoexcited electrons subsequently relaxed, with characteristic times of 200-500 ps depending on e, into Ti-related surface traps that possessed suitable energy to promote -NO2 reduction. The photoexcited holes migrated to long-lived surface traps with sufficient overpotential for the oxidization of both 2-propanol and water. On the basis of TA spectroscopy and photocurrent measurements, the position of the dopant-induced intra-gap level was estimated as 2.2 eV below the conduction band minimum.

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Section: Introductionmentioning

confidence: 99%

Charge carrier dynamics and visible light photocatalysis in vanadium-doped TiO2 nanoparticles

Rossi

Pasquini

Catone

et al. 2018

Applied Catalysis B: Environmental

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“…The fast component is linked to the trapping of the electron by the defect state located immediately below the conduction band, whereas the second time component is attributed to carrier trapping by deep-level trap states located near the center of the bandgap. 49 It is worth mentioning here that to understand the precise location of the intra-band defect states, we must turn to high-level theoretical investigations, which are beyond the scope of this study. After ZnS shelling, it is observed that for CIS and CISSe, the fast component still remains but with less amplitude, and the other component (with the hundreds of picosecond time constant before shelling) is almost completely removed.…”

Section: ■ Introductionmentioning

confidence: 99%

Direct Femtosecond Observation of Charge Carrier Recombination in Ternary Semiconductor Nanocrystals: The Effect of Composition and Shelling

et al. 2015

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Heavy-metal free ternary semiconductor nanocrystals are emerging as key materials in photoactive applications. However, the relative abundance of intrabandgap defect states and lack of understanding of their origins within this class of nanocrystals are major factors limiting their applicability. To remove these undesirable defect states which considerably shorten the lifetimes of photogenerated excited carriers, a detailed understanding about their origin and nature is required. In this report, we monitor the ultrafast charge carrier dynamics of CuInS 2 (CIS), CuInSSe (CISSe), and CuInSe 2 (CISe) nanocrystals, before and after ZnS shelling, using state-of-the-art time-resolved laser spectroscopy with broadband capabilities. The experimental results demonstrate the presence of both electron and hole trapping intra-bandgap states in the nanocrystals which can be removed significantly by ZnS shelling, and the carrier dynamics is slowed down. Another important observation remains the reduction of carrier lifetime in the presence of Se, and the shelling strategy is observed to be less effective at suppressing trap states. This study provides quantitative physical insights into the role of anion composition and shelling on the charge carrier dynamics in ternary CIS, CISSe, and CISe nanocrystals which are essential to improve their applicability for photovoltaics and optoelectronics.

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“…The kinetic traces can be fitted bi‐exponentially with less than 200 fs and ps time constants. The fs and ps time components can be assigned to surface and deep trapped states, respectively . Interestingly, upon increasing the thickness of the TiO 2 , the lifetime of the carriers decreases significantly.…”

Section: Resultsmentioning

confidence: 98%

Ultrathin‐Film Titania Photocatalyst on Nanocavity for CO₂ Reduction with Boosted Catalytic Efficiencies

Song

Liang

et al. 2018

Global Challenges

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Photocatalytic CO2 reduction with water to hydrocarbons represents a viable and sustainable process toward greenhouse gas reduction and fuel/chemical production. Development of more efficient catalysts is the key to mitigate the limits in photocatalytic processes. Here, a novel ultrathin‐film photocatalytic light absorber (UFPLA) with TiO2 films to design efficient photocatalytic CO2 conversion processes is created. The UFPLA structure conquers the intrinsic trade‐off between optical absorption and charge carrier extraction efficiency, that is, a solar absorber should be thick enough to absorb majority of the light allowable by its bandgap but thin enough to allow charge carrier extraction for reactions. The as‐obtained structures significantly improve TiO2 photocatalytic activity and selectivity to oxygenated hydrocarbons than the benchmark photocatalyst (Aeroxide P25). Remarkably, UFPLAs with 2‐nm‐thick TiO2 films result in hydrocarbon formation rates of 0.967 mmol g−1 h−1, corresponding to 1145 times higher activity than Aeroxide P25. This observation is confirmed by femtosecond transient absorption spectroscopic experiments where longer charge carrier lifetimes are recorded for the thinner films. The current work demonstrates a powerful strategy to control light absorption and catalysis in CO2 conversion and, therefore, creates new and transformative ways of converting solar energy and greenhouse gas to alcohol fuels/chemicals.

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Ultrafast Carrier Trapping of a Metal-Doped Titanium Dioxide Semiconductor Revealed by Femtosecond Transient Absorption Spectroscopy

Abstract: We explored for the first time the ultrafast carrier trapping of a metal-doped titanium dioxide (TiO2) semiconductor using broadband transient absorption (

Cited by 39 publications

References 42 publications

Charge carrier dynamics and visible light photocatalysis in vanadium-doped TiO2 nanoparticles

Charge carrier dynamics and visible light photocatalysis in vanadium-doped TiO2 nanoparticles

Direct Femtosecond Observation of Charge Carrier Recombination in Ternary Semiconductor Nanocrystals: The Effect of Composition and Shelling

Ultrathin‐Film Titania Photocatalyst on Nanocavity for CO₂ Reduction with Boosted Catalytic Efficiencies

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Ultrafast Carrier Trapping of a Metal-Doped Titanium Dioxide Semiconductor Revealed by Femtosecond Transient Absorption Spectroscopy

Abstract: We explored for the first time the ultrafast carrier trapping of a metal-doped titanium dioxide (TiO2) semiconductor using broadband transient absorption (

Cited by 39 publications

References 42 publications

Charge carrier dynamics and visible light photocatalysis in vanadium-doped TiO2 nanoparticles

Charge carrier dynamics and visible light photocatalysis in vanadium-doped TiO2 nanoparticles

Direct Femtosecond Observation of Charge Carrier Recombination in Ternary Semiconductor Nanocrystals: The Effect of Composition and Shelling

Ultrathin‐Film Titania Photocatalyst on Nanocavity for CO2 Reduction with Boosted Catalytic Efficiencies

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Product

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Ultrathin‐Film Titania Photocatalyst on Nanocavity for CO₂ Reduction with Boosted Catalytic Efficiencies