Electrophoretic deposition (EPD) is a simple technique for the uptake of nanoparticles into mesop... more Electrophoretic deposition (EPD) is a simple technique for the uptake of nanoparticles into mesoporous films, for example to graft semiconducting nanocrystals (quantum dots, QDs) on mesoporous oxide thick films acting as photoanodes in third generation solar cells. Here we study the uptake of colloidal QDs into mesoporous TiO 2 films using EPD. We examined PbS@CdS core@shell QDs, which are optically active in the near infrared (NIR) region of the solar spectrum and exhibit improved long-term stability toward oxidation compared to their pure PbS counterpart, as demonstrated by X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectroscopy. We applied Rutherford backscattering spectrometry (RBS) to obtain the Pb depth profile into the TiO 2 matrix. EPD duration in the range from 5 to 120 min and applied voltages from 50 to 200 V were considered. The applied electric field induces the fast anchoring of QDs to the oxide surface. Consequently, QD concentration in the solution contained in the mesoporous film drastically decreases, inducing a Fick-like diffusion of QDs. We modelled the entire process as a QD diffusion related to the formation of a QD concentration gradient, and a depth-independent QD anchoring, and were able to determine the electric field-induced diffusion coefficient D for QDs and the characteristic time for QD grafting, in very good agreement with the experiment. D increases from (1.5 AE 0.4) Â 10 À5 mm 2 s À1 at 50 V to (1.1 AE 0.3) Â 10 À3 mm 2 s À1 at 200 V. The dynamics of EPD may also be applied to other different colloidal QDs and quantum rod materials for the sensitization of mesoporous films. These results quantitatively describe the process of QD uptake during EPD, and can be used to tune the optical and optoelectronic properties of composite systems, which determine, for instance, the photoconversion efficiency in QD solar cells (QDSCs).
Small (Weinheim an der Bergstrasse, Germany), Jan 15, 2015
Core-shell quantum dots serve as self-calibrating, ultrasensitive, multiparametric, near-infrared... more Core-shell quantum dots serve as self-calibrating, ultrasensitive, multiparametric, near-infrared, and biocompatible temperature sensors. They allow temperature measurement with nanometer accuracy in the range 150-373 K, the broadest ever recorded for a nanothermometer, with sensitivities among the highest ever reported, which makes them essentially unique in the panorama of biocompatible nanothermometers with potential for in vivo biological thermal imaging and/or thermoablative therapy.
ABSTRACT The effect of PbS core size on the temperature-dependent photoluminescence (PL) of PbS/C... more ABSTRACT The effect of PbS core size on the temperature-dependent photoluminescence (PL) of PbS/CdS quantum dots (QDs) in the temperature range of 100-300 K was thoroughly investigated and compared with shell-free PbS QDs. The core/shell QDs show significantly smaller PL intensity variation with temperature at a smaller PbS size, while a larger activation energy when the PbS domain size is relatively large, suggesting both different density and different distribution of defects/traps in the PbS and PbS/CdS QDs. The most remarkable difference consists in the PbS size dependence of the energy gap temperature coefficient (dE/dT). The PbS/CdS QDs show unusual non-monotonic dE/dT variation, resulting in the reversal of the dE/dT difference between the PbS and PbS/CdS QDs at a larger PbS size. In combination with theoretical calculations, we find that, although lattice dilation and carrier-phonon coupling are generally considered as dominant terms, the unique negative contribution to dE/dT from the core/shell interfacial strain becomes most important in the relatively larger-core PbS@CdS QDs.
ABSTRACT We examine the effect of reaction time, temperature, molar ratio of precursors, capping ... more ABSTRACT We examine the effect of reaction time, temperature, molar ratio of precursors, capping ligands, and aging on the growth of PbS quantum dots in a “nonviscous”, solventless, mild-constant-temperature system with PbCl2 and S as precursors. It is found in our system that Ostwald ripening leads to bimodal photoluminescence corresponding to the bimodal size distribution of PbS quantum dots, as evidenced by transmission electron microscopy, in contrast to commonly reported single-peak broadening due to Ostwald ripening. The evolution of photoluminescence spectra mediated by Ostwald ripening is strongly affected by reaction parameters. Under certain conditions, the photoluminescence band exhibits some initial broadening upon the action of Ostwald ripening and then gradually transforms into a bimodal structure. In other cases, bimodal peaks rapidly appear as early as 1 min after the reaction starts. Moreover, it is found that the addition of an additional ligand trioctylphosphine immediately initiates the bimodal photoluminescence, which, however, on the basis of photoluminescence spectra characteristics is not thought to be associated with Ostwald ripening. For the bimodal emission structure, aging can greatly enhance the emission peak at shorter wavelength, but it does not affect the emission peak at longer wavelength. Using our simple system, we are able to synthesize PbS quantum dots with a narrow size distribution evidenced by a full width at half-maximum of the photoluminescence peak as low as 58 meV.
ABSTRACT Successful transfer of near-infrared emitting quantum dots (QDs) into water is critical ... more ABSTRACT Successful transfer of near-infrared emitting quantum dots (QDs) into water is critical for many biological applications. In this paper, PbS QDs capped by several types of most commonly used capping ligands are transferred from an organic solvent into water via poly(maleic anhydride-alt-1-octadecene)-co-poly(ethylene glycol). It is found that the variation of the structure and optical property of QDs upon water transfer highly depends on the type of capping ligands because of their different interactions with their surroundings (such as solvent molecules, polymers, and QD surface). This is in clear contrast to the common concept that amphiphilic polymers will not disturb the ligand structure on the QD surface during the transfer process, and thus the type of ligands will not bear any direct relevance with the variation of QDs and their properties. This work demonstrates that when oleic acid (OA) or OA/trioctylphosphine (TOP) ligands are used, the amphiphilic polymer approach is able to maintain the initial QD structure and high photostability in water; whereas, in the case of oleylamine (OLA) ligands, severe ligand etching takes place, which initiates Ostwald ripening, leading to double size distribution and, moreover, the total photoluminescence (PL) loss in a short time after water transfer. The complete darkening of PbS capped by OLA QDs is found to be mainly due to the introduction of many unpassivated surface atoms during the etching and Ostwald ripening process. Among all the samples, PbS QDs capped by OA/TOP ligands show the highest PL intensity, doubling that of PbS QDs capped by OLA or OA ligands after immediate water transfer. Meanwhile, the PL spectral shift after water transfer also varies among the samples. Our study suggests that the surface ligands do play a crucial role in the process of water transfer of PbS QDs, and “correct” ligands should be used to obtain high-quality water-soluble PbS QDs using the amphiphilic polymer approach.
ABSTRACT The luminescence switching behavior of CePO4:Tb has been widely studied upon an interfac... more ABSTRACT The luminescence switching behavior of CePO4:Tb has been widely studied upon an interfacial oxidation–reduction reaction where KMnO4 and ascorbic acid act as an oxidant and a reductant, respectively. However, the transformation of Mn-involved species derived from KMnO4 during the oxidation–reduction cycle and their effect on the luminescence properties of CePO4:Tb have not been explored so far. Here, we further study this interfacial reaction between CePO4:Tb and KMnO4 through various characterization techniques, such as X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. We find that an amorphous manganese oxide layer forms on the CePO4:Tb surface along with the partial oxidation of Ce(III) upon addition of KMnO4. In the subsequent reduction, the ascorbic acid not only reduces Ce(IV) to Ce(III) but also dissolves the formed manganese oxide. If manganese oxide is kept on the CePO4:Tb surface during the reduction treatment, the photoluminescence of Tb(III), due to the energy transfer from Ce(III) to Tb(III), would be restrained even if Ce(IV) ions were efficiently reduced. Although the degree of surface oxidation/reduction (Ce(III)/Ce(IV)) was considered to be a key factor for the luminescence quenching/recovery behavior in previous studies, there is a strong indication that the reaction product, e.g. manganese oxide, and associated surface defects generated from the oxidation–reduction reaction can disturb the photoluminescence of Tb(III) when they are not removed.
Proceedings of the National Academy of Sciences, 1996
The Sanfilippo syndrome type B is a lysosomal storage disorder caused by deficiency of alpha-N-ac... more The Sanfilippo syndrome type B is a lysosomal storage disorder caused by deficiency of alpha-N-acetylglucosaminidase; it is characterized by profound mental deterioration in childhood and death in the second decade. For understanding the molecular genetics of the disease and for future development of DNA-based therapy, we have cloned the cDNA and gene encoding alpha-N-acetylglucosaminidase. Cloning started with purification of the bovine enzyme and use of a conserved oligonucleotide sequence to probe a human cDNA library. The cDNA sequence was found to encode a protein of 743 amino acids, with a 20- to 23-aa signal peptide immediately preceding the amino terminus of the tissue enzyme and with six potential N-glycosylation sites. The 8.5-kb gene (NAGLU), interrupted by 5 introns, was localized to the 5'-flanking sequence of a known gene, EDH17B, on chromosome 17q21. Five mutations were identified in cells of patients with Sanfilippo syndrome type B: 503del10, R297X, R626X, R643H, and R674H. The occurrence of a frameshift and a nonsense mutation in homozygous form confirms the identity of the NAGLU gene.
Self-selected recovery of the photoluminescence (PL) of amphiphilic polymer encapsulated PbS quan... more Self-selected recovery of the photoluminescence (PL) of amphiphilic polymer encapsulated PbS quantum dots (QDs) was observed in water for the first time and possible mechanisms were proposed based on investigations by means of transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction and fluorescence spectroscopy. Water-soluble PbS QDs were synthesized by transferring monodispersed QDs capped with hydrophobic ligands of oleylamine from an organic solvent into water via amphiphilic polymers poly(maleic anhydride-alt-1-octadecene-co-poly(ethylene glycol)). The water transfer process leads to a double size distribution (5.6 ± 0.9 nm and 2.7 ± 0.4 nm), attributed to ligand etching together with Ostwald ripening, as well as the fast decay of PL. The automatic recovery of the PL in PbS QDs stored in water in the dark for 3 months was only observed for the subset of smaller QDs and is largely due to the removal of surface defects with aging, as evidenced by the decreased percentage of unpassivated surface atoms from XPS studies. In contrast, the PL of the subset of larger QDs in the same sample does not self-recover in water and can only be slightly recovered by transferring them into environments with less external quenches. The results strongly suggest that it is the surface defect in the larger QDs themselves, introduced during Ostwald ripening, that is primarily responsible for their non-emitting status or rather low PL intensity under different conditions. The increase of unpassivated Pb atoms in larger PbS QDs after the 3 month aging has been confirmed by XPS, which explains their non-recovery behavior in water. The PL-recovered QD sample in water is very stable and shows comparable photostability to the initial QDs dispersed in an organic phase.
Here we report the wet-chemical synthesis of asymmetric one-dimensional (1D) silver &... more Here we report the wet-chemical synthesis of asymmetric one-dimensional (1D) silver "nanocarrot" structures that exhibit mixed twins and stacking fault domains along the <111> direction. Oriented attachment is the dominant mechanism for anisotropic growth. Multipolar plasmon resonances up to fourth order were measured by optical extinction spectroscopy and electron energy-loss spectroscopy (EELS) and are in agreement with theoretical calculations. Compared with those of symmetric 1D nanostructures of similar length, the dipole modes of the nanocarrots show a clear red shift, and the EELS maps show an asymmetric distribution of the resonant plasmonic fields and a compression of the resonance node spacing toward the tail. In addition, increasing the length of the nanocarrots causes an increase in the intensity and a steady red shift of the longitudinal surface plasmon resonance peaks. The silver nanocarrots also show very high sensitivity to the refractive index of their environment (890 ± 87 nm per refractive index unit).
... 2006, 128, 2385– 2393 [ACS Full Text ACS Full Text ], [PubMed], [CAS] 5. Quantum Dot Solar Ce... more ... 2006, 128, 2385– 2393 [ACS Full Text ACS Full Text ], [PubMed], [CAS] 5. Quantum Dot Solar Cells. Harvesting Light Energy with CdSe Nanocrystals Molecularly Linked to Mesoscopic TiO2 Films. Robel, Istvan; Subramanian, Vaidyanathan; Kuno, Masaru; Kamat, Prashant V. ...
We study how the as-received chemical reagents of a commonly used ligand oleylamine (C18-amine) a... more We study how the as-received chemical reagents of a commonly used ligand oleylamine (C18-amine) and precursor PbCl2, each at two different purity statuses, affect the growth of PbS quantum dots in a solventless, relatively green, constant reaction-temperature synthesis system. It is found that the growth behavior of PbS quantum dots reflected from their absorption and photoluminescence spectra is quite sensitive to the purity status of the ligand and precursor under certain circumstances, while the lifetime and quantum yield of quantum dots exhibiting a monomodal or nearly monomodal photoluminescence band are not considerably affected. For instance, the effect of the ligand purity status is particularly evident when a higher PbCl2/S ratio is applied. The use of lower purity C18-amine leads to the growth showing much stronger temperature dependence and also facilitates the earlier entry of Ostwald process highlighted by a bimodal photoluminescence structure. Consistently, a 2 wt% increase in the PbCl2 purity from 98 wt% to 100 wt% (or the absence of 2 wt% of impurities) largely postpones the start of Ostwald process and thus significantly improves both absorption and photoluminescence spectra. These results imply that in order to produce PbS quantum dots with narrow absorption and photoluminescence peaks, one needs to optimize reaction parameters as well as select chemicals of appropriate purities. Moreover, the unintentional involvement of chemicals of different purity status may partially account for the irreproducibility problem often encountered in quantum dot synthesis.
ABSTRACT A two-step cation exchange procedure has been developed for synthesizing PbS/CdS core/sh... more ABSTRACT A two-step cation exchange procedure has been developed for synthesizing PbS/CdS core/shell quantum dots (QDs) with a much thicker shell than previously reported, which expands the flexibility of the current cation exchange approach. The thick-shell QDs allow relatively easy observation of the core/shell morphology by transmission electron microscopy as well as exhibiting characteristic absorption and emission of CdS when the shell thickness reaches 1.8 nm. X-ray diffraction patterns show gradual transformation from a rock salt PbS pattern to a zinc blend CdS pattern with increasing shell thickness and the overall diffraction pattern is indeed the same as that of the CdS standard when the shell is thicker than 3.6 nm. The thick-shell QDs were further analyzed by energy dispersive X-ray spectrometry. It is found that Pb only exists in the core region and is essentially absent in the shell region. All of these results consistently suggest that the shell is made of CdS, instead of ternary PbxCd1−xS alloy in thick-shell QDs. As direct experimental identification of the shell composition in thin-shell QDs is difficult, experimental data and calculations are combined to indirectly probe this issue. The comparison of band gap versus core size plots of different compositional models indicates that it is highly likely that the thin shell is also made of CdS. Importantly, these core/shell PbS/CdS QDs not only show significantly increased quantum yield up to 67% at the optimal shell thickness of about 0.7 nm, they are also much more photostable and thermally stable than the shell-free PbS QDs.
ABSTRACT We have synthesized and investigated the anisotropic growth of interesting silver nanori... more ABSTRACT We have synthesized and investigated the anisotropic growth of interesting silver nanorice. Its growth is kinetically controlled at 100 degrees C, and both oriented attachment and Ostwald ripening are involved, with the former growth mode dominating the anisotropic growth of the nanorice along the < 111 > direction. This one-directional growth is initiated by an indispensable seed-selection process, in which oxygen plays a critical role in oxidatively etching twinned silver crystals. The inhibition of this process by removing oxygen essentially blocks the nanorice growth. Although increasing reaction temperature to 120 degrees C accelerates the one-dimensional growth along the < 111 > direction, further temperature increase to 160 degrees C makes the oriented attachment dominated one-directional growth disappear; instead, the diffusion-controlled two-dimensional growth leads to the emergence of highly faceted truncated triangular and hexagonal plates mainly bound by low energy faces of {111}. Interestingly, we also found that the longitudinal surface plasmon resonance of the nanorice structures is highly sensitive to the refractive index of surrounding dielectric media, which predicts their promising applications as chemical or biological sensors. Moreover, the multipolar plasmonic resonances in these individual nanorice structures are visualized in real space, using high-resolution electron energy-loss spectroscopy.
In this study, we develop a reproducible and controllable microwave-assisted cation exchange appr... more In this study, we develop a reproducible and controllable microwave-assisted cation exchange approach, for the first time, to quickly synthesize high-quality, near-infrared emitting PbS/CdS core/shell quantum dots (QDs). These monodisperse QDs, emitting in the range of 1300-1600 nm, show a quantum yield as high as 57% that is ~1.4 times higher than that achieved by the same QDs prepared using conventional heating in an oil bath. To the best of our knowledge, it is the highest reproducible value reported to date for PbS-based QDs in this emission range. More importantly, the as-synthesized PbS/CdS QDs can self-assemble nearly perfectly and easily at the micrometer scale as a result of their uniform shape and narrow size distribution.
Electrophoretic deposition (EPD) is a simple technique for the uptake of nanoparticles into mesop... more Electrophoretic deposition (EPD) is a simple technique for the uptake of nanoparticles into mesoporous films, for example to graft semiconducting nanocrystals (quantum dots, QDs) on mesoporous oxide thick films acting as photoanodes in third generation solar cells. Here we study the uptake of colloidal QDs into mesoporous TiO 2 films using EPD. We examined PbS@CdS core@shell QDs, which are optically active in the near infrared (NIR) region of the solar spectrum and exhibit improved long-term stability toward oxidation compared to their pure PbS counterpart, as demonstrated by X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectroscopy. We applied Rutherford backscattering spectrometry (RBS) to obtain the Pb depth profile into the TiO 2 matrix. EPD duration in the range from 5 to 120 min and applied voltages from 50 to 200 V were considered. The applied electric field induces the fast anchoring of QDs to the oxide surface. Consequently, QD concentration in the solution contained in the mesoporous film drastically decreases, inducing a Fick-like diffusion of QDs. We modelled the entire process as a QD diffusion related to the formation of a QD concentration gradient, and a depth-independent QD anchoring, and were able to determine the electric field-induced diffusion coefficient D for QDs and the characteristic time for QD grafting, in very good agreement with the experiment. D increases from (1.5 AE 0.4) Â 10 À5 mm 2 s À1 at 50 V to (1.1 AE 0.3) Â 10 À3 mm 2 s À1 at 200 V. The dynamics of EPD may also be applied to other different colloidal QDs and quantum rod materials for the sensitization of mesoporous films. These results quantitatively describe the process of QD uptake during EPD, and can be used to tune the optical and optoelectronic properties of composite systems, which determine, for instance, the photoconversion efficiency in QD solar cells (QDSCs).
Small (Weinheim an der Bergstrasse, Germany), Jan 15, 2015
Core-shell quantum dots serve as self-calibrating, ultrasensitive, multiparametric, near-infrared... more Core-shell quantum dots serve as self-calibrating, ultrasensitive, multiparametric, near-infrared, and biocompatible temperature sensors. They allow temperature measurement with nanometer accuracy in the range 150-373 K, the broadest ever recorded for a nanothermometer, with sensitivities among the highest ever reported, which makes them essentially unique in the panorama of biocompatible nanothermometers with potential for in vivo biological thermal imaging and/or thermoablative therapy.
ABSTRACT The effect of PbS core size on the temperature-dependent photoluminescence (PL) of PbS/C... more ABSTRACT The effect of PbS core size on the temperature-dependent photoluminescence (PL) of PbS/CdS quantum dots (QDs) in the temperature range of 100-300 K was thoroughly investigated and compared with shell-free PbS QDs. The core/shell QDs show significantly smaller PL intensity variation with temperature at a smaller PbS size, while a larger activation energy when the PbS domain size is relatively large, suggesting both different density and different distribution of defects/traps in the PbS and PbS/CdS QDs. The most remarkable difference consists in the PbS size dependence of the energy gap temperature coefficient (dE/dT). The PbS/CdS QDs show unusual non-monotonic dE/dT variation, resulting in the reversal of the dE/dT difference between the PbS and PbS/CdS QDs at a larger PbS size. In combination with theoretical calculations, we find that, although lattice dilation and carrier-phonon coupling are generally considered as dominant terms, the unique negative contribution to dE/dT from the core/shell interfacial strain becomes most important in the relatively larger-core PbS@CdS QDs.
ABSTRACT We examine the effect of reaction time, temperature, molar ratio of precursors, capping ... more ABSTRACT We examine the effect of reaction time, temperature, molar ratio of precursors, capping ligands, and aging on the growth of PbS quantum dots in a “nonviscous”, solventless, mild-constant-temperature system with PbCl2 and S as precursors. It is found in our system that Ostwald ripening leads to bimodal photoluminescence corresponding to the bimodal size distribution of PbS quantum dots, as evidenced by transmission electron microscopy, in contrast to commonly reported single-peak broadening due to Ostwald ripening. The evolution of photoluminescence spectra mediated by Ostwald ripening is strongly affected by reaction parameters. Under certain conditions, the photoluminescence band exhibits some initial broadening upon the action of Ostwald ripening and then gradually transforms into a bimodal structure. In other cases, bimodal peaks rapidly appear as early as 1 min after the reaction starts. Moreover, it is found that the addition of an additional ligand trioctylphosphine immediately initiates the bimodal photoluminescence, which, however, on the basis of photoluminescence spectra characteristics is not thought to be associated with Ostwald ripening. For the bimodal emission structure, aging can greatly enhance the emission peak at shorter wavelength, but it does not affect the emission peak at longer wavelength. Using our simple system, we are able to synthesize PbS quantum dots with a narrow size distribution evidenced by a full width at half-maximum of the photoluminescence peak as low as 58 meV.
ABSTRACT Successful transfer of near-infrared emitting quantum dots (QDs) into water is critical ... more ABSTRACT Successful transfer of near-infrared emitting quantum dots (QDs) into water is critical for many biological applications. In this paper, PbS QDs capped by several types of most commonly used capping ligands are transferred from an organic solvent into water via poly(maleic anhydride-alt-1-octadecene)-co-poly(ethylene glycol). It is found that the variation of the structure and optical property of QDs upon water transfer highly depends on the type of capping ligands because of their different interactions with their surroundings (such as solvent molecules, polymers, and QD surface). This is in clear contrast to the common concept that amphiphilic polymers will not disturb the ligand structure on the QD surface during the transfer process, and thus the type of ligands will not bear any direct relevance with the variation of QDs and their properties. This work demonstrates that when oleic acid (OA) or OA/trioctylphosphine (TOP) ligands are used, the amphiphilic polymer approach is able to maintain the initial QD structure and high photostability in water; whereas, in the case of oleylamine (OLA) ligands, severe ligand etching takes place, which initiates Ostwald ripening, leading to double size distribution and, moreover, the total photoluminescence (PL) loss in a short time after water transfer. The complete darkening of PbS capped by OLA QDs is found to be mainly due to the introduction of many unpassivated surface atoms during the etching and Ostwald ripening process. Among all the samples, PbS QDs capped by OA/TOP ligands show the highest PL intensity, doubling that of PbS QDs capped by OLA or OA ligands after immediate water transfer. Meanwhile, the PL spectral shift after water transfer also varies among the samples. Our study suggests that the surface ligands do play a crucial role in the process of water transfer of PbS QDs, and “correct” ligands should be used to obtain high-quality water-soluble PbS QDs using the amphiphilic polymer approach.
ABSTRACT The luminescence switching behavior of CePO4:Tb has been widely studied upon an interfac... more ABSTRACT The luminescence switching behavior of CePO4:Tb has been widely studied upon an interfacial oxidation–reduction reaction where KMnO4 and ascorbic acid act as an oxidant and a reductant, respectively. However, the transformation of Mn-involved species derived from KMnO4 during the oxidation–reduction cycle and their effect on the luminescence properties of CePO4:Tb have not been explored so far. Here, we further study this interfacial reaction between CePO4:Tb and KMnO4 through various characterization techniques, such as X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. We find that an amorphous manganese oxide layer forms on the CePO4:Tb surface along with the partial oxidation of Ce(III) upon addition of KMnO4. In the subsequent reduction, the ascorbic acid not only reduces Ce(IV) to Ce(III) but also dissolves the formed manganese oxide. If manganese oxide is kept on the CePO4:Tb surface during the reduction treatment, the photoluminescence of Tb(III), due to the energy transfer from Ce(III) to Tb(III), would be restrained even if Ce(IV) ions were efficiently reduced. Although the degree of surface oxidation/reduction (Ce(III)/Ce(IV)) was considered to be a key factor for the luminescence quenching/recovery behavior in previous studies, there is a strong indication that the reaction product, e.g. manganese oxide, and associated surface defects generated from the oxidation–reduction reaction can disturb the photoluminescence of Tb(III) when they are not removed.
Proceedings of the National Academy of Sciences, 1996
The Sanfilippo syndrome type B is a lysosomal storage disorder caused by deficiency of alpha-N-ac... more The Sanfilippo syndrome type B is a lysosomal storage disorder caused by deficiency of alpha-N-acetylglucosaminidase; it is characterized by profound mental deterioration in childhood and death in the second decade. For understanding the molecular genetics of the disease and for future development of DNA-based therapy, we have cloned the cDNA and gene encoding alpha-N-acetylglucosaminidase. Cloning started with purification of the bovine enzyme and use of a conserved oligonucleotide sequence to probe a human cDNA library. The cDNA sequence was found to encode a protein of 743 amino acids, with a 20- to 23-aa signal peptide immediately preceding the amino terminus of the tissue enzyme and with six potential N-glycosylation sites. The 8.5-kb gene (NAGLU), interrupted by 5 introns, was localized to the 5'-flanking sequence of a known gene, EDH17B, on chromosome 17q21. Five mutations were identified in cells of patients with Sanfilippo syndrome type B: 503del10, R297X, R626X, R643H, and R674H. The occurrence of a frameshift and a nonsense mutation in homozygous form confirms the identity of the NAGLU gene.
Self-selected recovery of the photoluminescence (PL) of amphiphilic polymer encapsulated PbS quan... more Self-selected recovery of the photoluminescence (PL) of amphiphilic polymer encapsulated PbS quantum dots (QDs) was observed in water for the first time and possible mechanisms were proposed based on investigations by means of transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction and fluorescence spectroscopy. Water-soluble PbS QDs were synthesized by transferring monodispersed QDs capped with hydrophobic ligands of oleylamine from an organic solvent into water via amphiphilic polymers poly(maleic anhydride-alt-1-octadecene-co-poly(ethylene glycol)). The water transfer process leads to a double size distribution (5.6 ± 0.9 nm and 2.7 ± 0.4 nm), attributed to ligand etching together with Ostwald ripening, as well as the fast decay of PL. The automatic recovery of the PL in PbS QDs stored in water in the dark for 3 months was only observed for the subset of smaller QDs and is largely due to the removal of surface defects with aging, as evidenced by the decreased percentage of unpassivated surface atoms from XPS studies. In contrast, the PL of the subset of larger QDs in the same sample does not self-recover in water and can only be slightly recovered by transferring them into environments with less external quenches. The results strongly suggest that it is the surface defect in the larger QDs themselves, introduced during Ostwald ripening, that is primarily responsible for their non-emitting status or rather low PL intensity under different conditions. The increase of unpassivated Pb atoms in larger PbS QDs after the 3 month aging has been confirmed by XPS, which explains their non-recovery behavior in water. The PL-recovered QD sample in water is very stable and shows comparable photostability to the initial QDs dispersed in an organic phase.
Here we report the wet-chemical synthesis of asymmetric one-dimensional (1D) silver &... more Here we report the wet-chemical synthesis of asymmetric one-dimensional (1D) silver "nanocarrot" structures that exhibit mixed twins and stacking fault domains along the <111> direction. Oriented attachment is the dominant mechanism for anisotropic growth. Multipolar plasmon resonances up to fourth order were measured by optical extinction spectroscopy and electron energy-loss spectroscopy (EELS) and are in agreement with theoretical calculations. Compared with those of symmetric 1D nanostructures of similar length, the dipole modes of the nanocarrots show a clear red shift, and the EELS maps show an asymmetric distribution of the resonant plasmonic fields and a compression of the resonance node spacing toward the tail. In addition, increasing the length of the nanocarrots causes an increase in the intensity and a steady red shift of the longitudinal surface plasmon resonance peaks. The silver nanocarrots also show very high sensitivity to the refractive index of their environment (890 ± 87 nm per refractive index unit).
... 2006, 128, 2385– 2393 [ACS Full Text ACS Full Text ], [PubMed], [CAS] 5. Quantum Dot Solar Ce... more ... 2006, 128, 2385– 2393 [ACS Full Text ACS Full Text ], [PubMed], [CAS] 5. Quantum Dot Solar Cells. Harvesting Light Energy with CdSe Nanocrystals Molecularly Linked to Mesoscopic TiO2 Films. Robel, Istvan; Subramanian, Vaidyanathan; Kuno, Masaru; Kamat, Prashant V. ...
We study how the as-received chemical reagents of a commonly used ligand oleylamine (C18-amine) a... more We study how the as-received chemical reagents of a commonly used ligand oleylamine (C18-amine) and precursor PbCl2, each at two different purity statuses, affect the growth of PbS quantum dots in a solventless, relatively green, constant reaction-temperature synthesis system. It is found that the growth behavior of PbS quantum dots reflected from their absorption and photoluminescence spectra is quite sensitive to the purity status of the ligand and precursor under certain circumstances, while the lifetime and quantum yield of quantum dots exhibiting a monomodal or nearly monomodal photoluminescence band are not considerably affected. For instance, the effect of the ligand purity status is particularly evident when a higher PbCl2/S ratio is applied. The use of lower purity C18-amine leads to the growth showing much stronger temperature dependence and also facilitates the earlier entry of Ostwald process highlighted by a bimodal photoluminescence structure. Consistently, a 2 wt% increase in the PbCl2 purity from 98 wt% to 100 wt% (or the absence of 2 wt% of impurities) largely postpones the start of Ostwald process and thus significantly improves both absorption and photoluminescence spectra. These results imply that in order to produce PbS quantum dots with narrow absorption and photoluminescence peaks, one needs to optimize reaction parameters as well as select chemicals of appropriate purities. Moreover, the unintentional involvement of chemicals of different purity status may partially account for the irreproducibility problem often encountered in quantum dot synthesis.
ABSTRACT A two-step cation exchange procedure has been developed for synthesizing PbS/CdS core/sh... more ABSTRACT A two-step cation exchange procedure has been developed for synthesizing PbS/CdS core/shell quantum dots (QDs) with a much thicker shell than previously reported, which expands the flexibility of the current cation exchange approach. The thick-shell QDs allow relatively easy observation of the core/shell morphology by transmission electron microscopy as well as exhibiting characteristic absorption and emission of CdS when the shell thickness reaches 1.8 nm. X-ray diffraction patterns show gradual transformation from a rock salt PbS pattern to a zinc blend CdS pattern with increasing shell thickness and the overall diffraction pattern is indeed the same as that of the CdS standard when the shell is thicker than 3.6 nm. The thick-shell QDs were further analyzed by energy dispersive X-ray spectrometry. It is found that Pb only exists in the core region and is essentially absent in the shell region. All of these results consistently suggest that the shell is made of CdS, instead of ternary PbxCd1−xS alloy in thick-shell QDs. As direct experimental identification of the shell composition in thin-shell QDs is difficult, experimental data and calculations are combined to indirectly probe this issue. The comparison of band gap versus core size plots of different compositional models indicates that it is highly likely that the thin shell is also made of CdS. Importantly, these core/shell PbS/CdS QDs not only show significantly increased quantum yield up to 67% at the optimal shell thickness of about 0.7 nm, they are also much more photostable and thermally stable than the shell-free PbS QDs.
ABSTRACT We have synthesized and investigated the anisotropic growth of interesting silver nanori... more ABSTRACT We have synthesized and investigated the anisotropic growth of interesting silver nanorice. Its growth is kinetically controlled at 100 degrees C, and both oriented attachment and Ostwald ripening are involved, with the former growth mode dominating the anisotropic growth of the nanorice along the < 111 > direction. This one-directional growth is initiated by an indispensable seed-selection process, in which oxygen plays a critical role in oxidatively etching twinned silver crystals. The inhibition of this process by removing oxygen essentially blocks the nanorice growth. Although increasing reaction temperature to 120 degrees C accelerates the one-dimensional growth along the < 111 > direction, further temperature increase to 160 degrees C makes the oriented attachment dominated one-directional growth disappear; instead, the diffusion-controlled two-dimensional growth leads to the emergence of highly faceted truncated triangular and hexagonal plates mainly bound by low energy faces of {111}. Interestingly, we also found that the longitudinal surface plasmon resonance of the nanorice structures is highly sensitive to the refractive index of surrounding dielectric media, which predicts their promising applications as chemical or biological sensors. Moreover, the multipolar plasmonic resonances in these individual nanorice structures are visualized in real space, using high-resolution electron energy-loss spectroscopy.
In this study, we develop a reproducible and controllable microwave-assisted cation exchange appr... more In this study, we develop a reproducible and controllable microwave-assisted cation exchange approach, for the first time, to quickly synthesize high-quality, near-infrared emitting PbS/CdS core/shell quantum dots (QDs). These monodisperse QDs, emitting in the range of 1300-1600 nm, show a quantum yield as high as 57% that is ~1.4 times higher than that achieved by the same QDs prepared using conventional heating in an oil bath. To the best of our knowledge, it is the highest reproducible value reported to date for PbS-based QDs in this emission range. More importantly, the as-synthesized PbS/CdS QDs can self-assemble nearly perfectly and easily at the micrometer scale as a result of their uniform shape and narrow size distribution.
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