A femtosecond fluorescence upconversion study is reported for HBO in solution, as well as for HBO... more A femtosecond fluorescence upconversion study is reported for HBO in solution, as well as for HBO incorporated in DNA. The typical time for the excited-state intramolecular proton-transfer reaction of the syn-enol tautomer in solution and in DNA has been determined to be 150 fs. In addition, the lifetimes of the keto, the anti-enol and the ‘solvated enol’ tautomer forms were determined in protic solvents, aprotic solvents and DNA. Picosecond rise and decay components in the fluorescence transients with characteristic times between 3 and 25 ps are also observed and attributed to the effects of vibrational cooling.
... Email: Dr. Osama K. Abou-Zied (abouzied@squ.edu.om). *Correspondence: Dr. Osama K. Abou-Zied,... more ... Email: Dr. Osama K. Abou-Zied (abouzied@squ.edu.om). *Correspondence: Dr. Osama K. Abou-Zied, Department of Chemistry, Faculty of Science, Sultan Qaboos University, PO Box 36, Postal Code 123, Muscat (Sultanate of Oman), Fax: (+968) 2414-1469. Publication History. ...
The incorporation of gold nanorod-modified TiO2 nanoparticles (TiO2/AuNRs) along with cobalt-imid... more The incorporation of gold nanorod-modified TiO2 nanoparticles (TiO2/AuNRs) along with cobalt-imidazolate frameworks (ZIF-67) into the photoanode of dye-sensitized solar cells resulted in a notable enhancement in energy conversion efficiency.
Abstract Photoluminescence (PL) quenching of nanoassemblies of CuInS2/ZnS quantum dots (CIS QDs) ... more Abstract Photoluminescence (PL) quenching of nanoassemblies of CuInS2/ZnS quantum dots (CIS QDs) and rhodamine 560 molecules (Rh560) is spectroscopically investigated by steady-state and femtosecond-to-nanosecond time-resolved techniques. Fluorescence lifetime measurements of CIS QDs show a bi-exponential decay (time constants ca. 650 ns and 210 ns) that are assigned to the radiative recombination of delocalized CB electrons with localized holes, presumably associated with Cu-related defect sites. A trapped electron recombines nonradiatively with the localized hole. That means, electron trapping is the first step in the nonradiative recombination pathway in CIS QDs. The traps are of surface origin and are likely associated with unpassivated dangling bonds. In this work, we controlled the trap density by varying the amount of Rh560 on the QD surface and monitoring the electron trapping in different time scales. Transient absorption measurements of the CIS-Rh560 assemblies resolved the fast component of electron trapping that occurs in tens to hundreds of picoseconds, while fluorescence lifetime measurements resolved the slow components of trapping that occur in hundreds of nanoseconds. Unlike the case of more traditional CdSe/ZnS QDs, the PL lifetime of CIS QDs approaches the typical time scale of fluorescence intermittency. As a result, the excited state of CIS QDs is vulnerable to the blinking process. In the CIS-Rh560 assembly, trapping of CB electrons increases with dye loading which eventually prolongs the dark (or dim) period and therefore reduces the fluorescence quantum yield of CIS QDs. The appearance of short lifetime components (ca. 0.5–6.9 ns) in the QD-dye assembly hints that Auger quenching process and/or electron-phonon coupling seems to play a major role in the PL quenching process.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, Feb 1, 2022
Carbon nanoparticles (CNPs) are getting wide attention due to their fluorescence and low level of... more Carbon nanoparticles (CNPs) are getting wide attention due to their fluorescence and low level of toxicity compared to other semiconducting photoluminescent materials. CNPs show strong 'solvatochromism', and the emission mechanism is still under discussion. Florescent carbon in the form of films would tremendously increase its potential for applications. In this work, we report for the first time the fluorescent emission characteristics of carbon films formed by aggregation of CNPs. Films of carbon were grown on glass substrates by using a novelCold Vapour Deposition System. We have performed a detailed comparative study of the emission spectra of film and CNPs (prepared using the microwave synthesis method) in various solvents. A qualitative model based on solvatochromism of CNPs is used to understand the emission pathways in the film.
A femtosecond fluorescence upconversion study is reported for HBO in solution, as well as for HBO... more A femtosecond fluorescence upconversion study is reported for HBO in solution, as well as for HBO incorporated in DNA. The typical time for the excited-state intramolecular proton-transfer reaction of the syn-enol tautomer in solution and in DNA has been determined to be 150 fs. In addition, the lifetimes of the keto, the anti-enol and the ‘solvated enol’ tautomer forms were determined in protic solvents, aprotic solvents and DNA. Picosecond rise and decay components in the fluorescence transients with characteristic times between 3 and 25 ps are also observed and attributed to the effects of vibrational cooling.
... Email: Dr. Osama K. Abou-Zied (abouzied@squ.edu.om). *Correspondence: Dr. Osama K. Abou-Zied,... more ... Email: Dr. Osama K. Abou-Zied (abouzied@squ.edu.om). *Correspondence: Dr. Osama K. Abou-Zied, Department of Chemistry, Faculty of Science, Sultan Qaboos University, PO Box 36, Postal Code 123, Muscat (Sultanate of Oman), Fax: (+968) 2414-1469. Publication History. ...
The incorporation of gold nanorod-modified TiO2 nanoparticles (TiO2/AuNRs) along with cobalt-imid... more The incorporation of gold nanorod-modified TiO2 nanoparticles (TiO2/AuNRs) along with cobalt-imidazolate frameworks (ZIF-67) into the photoanode of dye-sensitized solar cells resulted in a notable enhancement in energy conversion efficiency.
Abstract Photoluminescence (PL) quenching of nanoassemblies of CuInS2/ZnS quantum dots (CIS QDs) ... more Abstract Photoluminescence (PL) quenching of nanoassemblies of CuInS2/ZnS quantum dots (CIS QDs) and rhodamine 560 molecules (Rh560) is spectroscopically investigated by steady-state and femtosecond-to-nanosecond time-resolved techniques. Fluorescence lifetime measurements of CIS QDs show a bi-exponential decay (time constants ca. 650 ns and 210 ns) that are assigned to the radiative recombination of delocalized CB electrons with localized holes, presumably associated with Cu-related defect sites. A trapped electron recombines nonradiatively with the localized hole. That means, electron trapping is the first step in the nonradiative recombination pathway in CIS QDs. The traps are of surface origin and are likely associated with unpassivated dangling bonds. In this work, we controlled the trap density by varying the amount of Rh560 on the QD surface and monitoring the electron trapping in different time scales. Transient absorption measurements of the CIS-Rh560 assemblies resolved the fast component of electron trapping that occurs in tens to hundreds of picoseconds, while fluorescence lifetime measurements resolved the slow components of trapping that occur in hundreds of nanoseconds. Unlike the case of more traditional CdSe/ZnS QDs, the PL lifetime of CIS QDs approaches the typical time scale of fluorescence intermittency. As a result, the excited state of CIS QDs is vulnerable to the blinking process. In the CIS-Rh560 assembly, trapping of CB electrons increases with dye loading which eventually prolongs the dark (or dim) period and therefore reduces the fluorescence quantum yield of CIS QDs. The appearance of short lifetime components (ca. 0.5–6.9 ns) in the QD-dye assembly hints that Auger quenching process and/or electron-phonon coupling seems to play a major role in the PL quenching process.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, Feb 1, 2022
Carbon nanoparticles (CNPs) are getting wide attention due to their fluorescence and low level of... more Carbon nanoparticles (CNPs) are getting wide attention due to their fluorescence and low level of toxicity compared to other semiconducting photoluminescent materials. CNPs show strong 'solvatochromism', and the emission mechanism is still under discussion. Florescent carbon in the form of films would tremendously increase its potential for applications. In this work, we report for the first time the fluorescent emission characteristics of carbon films formed by aggregation of CNPs. Films of carbon were grown on glass substrates by using a novelCold Vapour Deposition System. We have performed a detailed comparative study of the emission spectra of film and CNPs (prepared using the microwave synthesis method) in various solvents. A qualitative model based on solvatochromism of CNPs is used to understand the emission pathways in the film.
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