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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.


Related in: MedlinePlus

Resonance Raman spectrum of CdS/TiO2 in comparison with the bare TiO2 film, at 514.5 nm. Dashed and dotted lines depict the spectral deconvolution to the CdS and TiO2 vibrational modes, respectively. The inset shows the Raman spectrum of PbS/TiO2 at 785 nm.
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Figure 2: Resonance Raman spectrum of CdS/TiO2 in comparison with the bare TiO2 film, at 514.5 nm. Dashed and dotted lines depict the spectral deconvolution to the CdS and TiO2 vibrational modes, respectively. The inset shows the Raman spectrum of PbS/TiO2 at 785 nm.

Mentions: The structural characteristics of the QD sensitized TiO2 films were investigated by resonance Raman measurements under vacuum in order to avoid air degradation. Figure 2 shows the Raman spectrum of CdS/TiO2 (9 SILAR cycles) at 514.5 nm, which is close to the absorption edge of the CdS nanocrystals and thus allows their resonant excitation. The characteristic Raman-active phonons of the underlying TiO2 substrate can be readily identified in comparison with the bare TiO2 electrode, the most intense being the low frequency anatase Eg mode at approximately 142 cm-1 [3], together with the resonantly excited longitudinal optical (LO) phonon of CdS QDs at approximately 300 cm-1 [20]. Spectral analysis reveals a slight asymmetric broadening of the CdS LO mode at the low frequency side, which can be effectively fitted to the superposition of two peaks, the LO mode at 301 cm-1 with full width at half maximum (FWHM) of 25 cm-1 and a broad low frequency mode at 277 cm-1 with FWHM of approximately 109 cm-1. Moreover, resonant excitation allows identifying the first (2 LO) and second (3 LO) overtones of the CdS nanoctystals at 604 and approximately 900 cm-1, respectively. The frequency of the LO peak matches bulk CdS (301 cm-1), whereas its width is considerably larger than the corresponding bulk value (approximately 12 cm-1) [20]. The broadening of the LO peak together with its asymmetric lineshape corroborates the presence of a broad size distribution of CdS nanocrystals and the absence of strong phonon confinement effects [21], in agreement with the features of the CdS/TiO2 optical absorbance.


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)

Resonance Raman spectrum of CdS/TiO2 in comparison with the bare TiO2 film, at 514.5 nm. Dashed and dotted lines depict the spectral deconvolution to the CdS and TiO2 vibrational modes, respectively. The inset shows the Raman spectrum of PbS/TiO2 at 785 nm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 2: Resonance Raman spectrum of CdS/TiO2 in comparison with the bare TiO2 film, at 514.5 nm. Dashed and dotted lines depict the spectral deconvolution to the CdS and TiO2 vibrational modes, respectively. The inset shows the Raman spectrum of PbS/TiO2 at 785 nm.
Mentions: The structural characteristics of the QD sensitized TiO2 films were investigated by resonance Raman measurements under vacuum in order to avoid air degradation. Figure 2 shows the Raman spectrum of CdS/TiO2 (9 SILAR cycles) at 514.5 nm, which is close to the absorption edge of the CdS nanocrystals and thus allows their resonant excitation. The characteristic Raman-active phonons of the underlying TiO2 substrate can be readily identified in comparison with the bare TiO2 electrode, the most intense being the low frequency anatase Eg mode at approximately 142 cm-1 [3], together with the resonantly excited longitudinal optical (LO) phonon of CdS QDs at approximately 300 cm-1 [20]. Spectral analysis reveals a slight asymmetric broadening of the CdS LO mode at the low frequency side, which can be effectively fitted to the superposition of two peaks, the LO mode at 301 cm-1 with full width at half maximum (FWHM) of 25 cm-1 and a broad low frequency mode at 277 cm-1 with FWHM of approximately 109 cm-1. Moreover, resonant excitation allows identifying the first (2 LO) and second (3 LO) overtones of the CdS nanoctystals at 604 and approximately 900 cm-1, respectively. The frequency of the LO peak matches bulk CdS (301 cm-1), whereas its width is considerably larger than the corresponding bulk value (approximately 12 cm-1) [20]. The broadening of the LO peak together with its asymmetric lineshape corroborates the presence of a broad size distribution of CdS nanocrystals and the absence of strong phonon confinement effects [21], in agreement with the features of the CdS/TiO2 optical absorbance.

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