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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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PL spectra of CdS/glass and CdS/TiO2 films excited at 476.5 nm. The inset shows the PL spectrum of PbS/TiO2 obtained with 785 nm excitation.
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Figure 4: PL spectra of CdS/glass and CdS/TiO2 films excited at 476.5 nm. The inset shows the PL spectrum of PbS/TiO2 obtained with 785 nm excitation.

Mentions: Figure 4 shows the PL spectra acquired simultaneously with the Raman signal of the CdS/TiO2 under anaerobic conditions. To explore the charge injection efficiency for the QDs to the TiO2 substrate, CdS nanocrystals were deposited on microscopic glass employing 9 SILAR cycles, leading to a film with similar optical and Raman spectroscopic characteristics to that grown on TiO2. Comparison of the corresponding PL spectra, after subtraction of the relatively weak emission of the glass substrate, reveals significant changes between the CdS/TiO2 and CdS/glass films. The PL spectra of CdS/glass exhibits a strong component at about 530 nm, which is close to the band gap emission of bulk CdS arising from radiative excitonic recombination, while a rather broad emission band occurs at 625 nm most likely due to the recombination of trapped carriers by defect states [24]. The frequency of the former emission band indicates the absence of significant quantum size effects, further supporting the growth of nanocrystals with size appreciably larger than the Bohr exciton radius of CdS (approximately 2.8 nm). Moreover, the width of the CdS excitonic peak (FWHM ~ 80 nm) in the CdS/glass film exceeds largely that of bulk CdS (FWHM ~ 20 nm) [24], indicative of a broad size distribution of the SILAR deposited CdS nanocrystals. However, upon CdS deposition on TiO2, the PL intensity of the excitonic emission is drastically suppressed, verifying the effective quenching of the radiative recombination of photoexcited carriers by electron transfer from CdS to TiO2.


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)

PL spectra of CdS/glass and CdS/TiO2 films excited at 476.5 nm. The inset shows the PL spectrum of PbS/TiO2 obtained with 785 nm excitation.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 4: PL spectra of CdS/glass and CdS/TiO2 films excited at 476.5 nm. The inset shows the PL spectrum of PbS/TiO2 obtained with 785 nm excitation.
Mentions: Figure 4 shows the PL spectra acquired simultaneously with the Raman signal of the CdS/TiO2 under anaerobic conditions. To explore the charge injection efficiency for the QDs to the TiO2 substrate, CdS nanocrystals were deposited on microscopic glass employing 9 SILAR cycles, leading to a film with similar optical and Raman spectroscopic characteristics to that grown on TiO2. Comparison of the corresponding PL spectra, after subtraction of the relatively weak emission of the glass substrate, reveals significant changes between the CdS/TiO2 and CdS/glass films. The PL spectra of CdS/glass exhibits a strong component at about 530 nm, which is close to the band gap emission of bulk CdS arising from radiative excitonic recombination, while a rather broad emission band occurs at 625 nm most likely due to the recombination of trapped carriers by defect states [24]. The frequency of the former emission band indicates the absence of significant quantum size effects, further supporting the growth of nanocrystals with size appreciably larger than the Bohr exciton radius of CdS (approximately 2.8 nm). Moreover, the width of the CdS excitonic peak (FWHM ~ 80 nm) in the CdS/glass film exceeds largely that of bulk CdS (FWHM ~ 20 nm) [24], indicative of a broad size distribution of the SILAR deposited CdS nanocrystals. However, upon CdS deposition on TiO2, the PL intensity of the excitonic emission is drastically suppressed, verifying the effective quenching of the radiative recombination of photoexcited carriers by electron transfer from CdS to TiO2.

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