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Nanostructured titania films sensitized by quantum dot chalcogenides.

Kontos AG, Likodimos V, Vassalou E, Kapogianni I, Raptis YS, Raptis C, Falaras P - Nanoscale Res Lett (2011)

Bottom Line: The optical absorbance of CdS/TiO2 can be tuned over a narrow spectral range.On the other side PbS/TiO2 exhibits a remarkable band gap tunability extending from the visible to the near infrared range, due to the distinct quantum size effects of PbS quantum dots.Degradation effects are much less pronounced for CdS/TiO2 that is appreciably more stable, though it degrades readily upon visible light illumination.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Physical Chemistry, NCSR "Demokritos", Aghia Paraskevi Attikis, Athens 15310, Greece. akontos@chem.demokritos.gr.

ABSTRACT
The optical and structural properties of cadmium and lead sulfide nanocrystals deposited on mesoporous TiO2 substrates via the successive ionic layer adsorption and reaction method were comparatively investigated by reflectance, transmittance, micro-Raman and photoluminescence measurements. Enhanced interfacial electron transfer is evidenced upon direct growth of both CdS and PbS on TiO2 through the marked quenching of their excitonic emission. The optical absorbance of CdS/TiO2 can be tuned over a narrow spectral range. On the other side PbS/TiO2 exhibits a remarkable band gap tunability extending from the visible to the near infrared range, due to the distinct quantum size effects of PbS quantum dots. However, PbS/TiO2 suffers from severe degradation upon air exposure. Degradation effects are much less pronounced for CdS/TiO2 that is appreciably more stable, though it degrades readily upon visible light illumination.

No MeSH data available.


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Absorbance spectra of the mesoporous TiO2 films upon SILAR deposition of (a) CdS and (b) PbS. Numbers correspond to the different SILAR cycles. The spectra of PbS/TiO2 after 90 min air exposure are also included in (b).
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Figure 1: Absorbance spectra of the mesoporous TiO2 films upon SILAR deposition of (a) CdS and (b) PbS. Numbers correspond to the different SILAR cycles. The spectra of PbS/TiO2 after 90 min air exposure are also included in (b).

Mentions: Figure 1a shows the evolution of the CdS/TiO2 absorbance, calculated from the corresponding transmittance and reflectance spectra, for successive SILAR cycles compared to that of the bare TiO2 films. Significant absorption in the visible range is thus observed, indicating the formation of CdS nanocrystals with gradually increasing concentration with the SILAR cycles. However, the distinct excitonic peaks, commonly observed for colloidal CdS QDs with a narrow size distribution, cannot be resolved, implying rather broad size dispersion for the SILAR deposited QDs. Moreover, the CdS/TiO2 absorption edge reached 585 nm upon completion of the ninth coating cycle. This value is close to that expected for bulk CdS, whose energy gap is approximately 2.4 eV, complying with the formation of nanocrystals with size exceeding 6 nm, above which quantum size effects essentially cease for CdS QDs [17]. On the other hand, an appreciable increase of the mean CdS particle size can be inferred from the gradual red-shift of the absorption edge, most prominent for the initial SILAR cycles. This is indicative of weak quantum size effects, pertaining for CdS nanocrystals with diameters slightly below 6 nm.


Nanostructured titania films sensitized by quantum dot chalcogenides.

Kontos AG, Likodimos V, Vassalou E, Kapogianni I, Raptis YS, Raptis C, Falaras P - Nanoscale Res Lett (2011)

Absorbance spectra of the mesoporous TiO2 films upon SILAR deposition of (a) CdS and (b) PbS. Numbers correspond to the different SILAR cycles. The spectra of PbS/TiO2 after 90 min air exposure are also included in (b).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211329&req=5

Figure 1: Absorbance spectra of the mesoporous TiO2 films upon SILAR deposition of (a) CdS and (b) PbS. Numbers correspond to the different SILAR cycles. The spectra of PbS/TiO2 after 90 min air exposure are also included in (b).
Mentions: Figure 1a shows the evolution of the CdS/TiO2 absorbance, calculated from the corresponding transmittance and reflectance spectra, for successive SILAR cycles compared to that of the bare TiO2 films. Significant absorption in the visible range is thus observed, indicating the formation of CdS nanocrystals with gradually increasing concentration with the SILAR cycles. However, the distinct excitonic peaks, commonly observed for colloidal CdS QDs with a narrow size distribution, cannot be resolved, implying rather broad size dispersion for the SILAR deposited QDs. Moreover, the CdS/TiO2 absorption edge reached 585 nm upon completion of the ninth coating cycle. This value is close to that expected for bulk CdS, whose energy gap is approximately 2.4 eV, complying with the formation of nanocrystals with size exceeding 6 nm, above which quantum size effects essentially cease for CdS QDs [17]. On the other hand, an appreciable increase of the mean CdS particle size can be inferred from the gradual red-shift of the absorption edge, most prominent for the initial SILAR cycles. This is indicative of weak quantum size effects, pertaining for CdS nanocrystals with diameters slightly below 6 nm.

Bottom Line: The optical absorbance of CdS/TiO2 can be tuned over a narrow spectral range.On the other side PbS/TiO2 exhibits a remarkable band gap tunability extending from the visible to the near infrared range, due to the distinct quantum size effects of PbS quantum dots.Degradation effects are much less pronounced for CdS/TiO2 that is appreciably more stable, though it degrades readily upon visible light illumination.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Physical Chemistry, NCSR "Demokritos", Aghia Paraskevi Attikis, Athens 15310, Greece. akontos@chem.demokritos.gr.

ABSTRACT
The optical and structural properties of cadmium and lead sulfide nanocrystals deposited on mesoporous TiO2 substrates via the successive ionic layer adsorption and reaction method were comparatively investigated by reflectance, transmittance, micro-Raman and photoluminescence measurements. Enhanced interfacial electron transfer is evidenced upon direct growth of both CdS and PbS on TiO2 through the marked quenching of their excitonic emission. The optical absorbance of CdS/TiO2 can be tuned over a narrow spectral range. On the other side PbS/TiO2 exhibits a remarkable band gap tunability extending from the visible to the near infrared range, due to the distinct quantum size effects of PbS quantum dots. However, PbS/TiO2 suffers from severe degradation upon air exposure. Degradation effects are much less pronounced for CdS/TiO2 that is appreciably more stable, though it degrades readily upon visible light illumination.

No MeSH data available.


Related in: MedlinePlus