Size-dependent photoinduced transparency in colloidal CdTe quantum dots in the strong confinement regime: an inverse linear relationship.

Nanomaterials have been investigated as saturable absorbers for ultrafast lasers because of their large photoinduced transparency related to ground-state bleaching. However, the quantum dot size effect on the photoinduced transparency in the strong confinement regime has not been explored due to the challenge of accurately measuring the ground state and the excited-state absorption cross-sections. At the same time, these optical properties are essential to calculate several chemical and physical quantities at the nanoscale. In this context, we have employed the photoluminescence saturation method to determine the ground-state absorption cross-section and the femtosecond open-aperture Z-scan technique to investigate the size-dependent ground-state bleaching of glutathione-capped CdTe QDs synthesized in an aqueous medium. The results were modeled using rate equations within the three-energy levels approach. Our results pointed out that the photoinduced transparency rate at the 1S3/2(h) → 1S(e) transition peak presents an inverse linear relationship with the QD diameter (from 2.2 nm up to 3 nm). Otherwise, the larger QDs have a higher ground-state cross-section, which is directly proportional to the ground-state bleaching. To explain this apparent contradiction, we calculate the effective absorption coefficient αeff = σ/V (σ is the absorption cross section and V is the QD volume) for the QDs and observed that the smaller QDs have a higher absorption from the ground to the first excited state, corroborating our results. Finally, our results showed that the saturable absorption effect in CdTe-QDs is slightly higher than that obtained for graphene and other 2D materials and smaller than the black phosphorus in the visible region.

Photoreactivity of a quantum dot-ruthenium nitrosyl conjugate.

We describe the use of cadmium telluride quantum dots (CdTe QDs) as antennas for the photosensitization of nitric oxide release from a ruthenium nitrosyl complex with visible light excitation. The CdTe QDs were capped with mercaptopropionic acid to make them water-soluble, and the ruthenium nitrosyl complex was cis-[Ru(NO)(4-ampy)(bpy)2](3+) (Ru-NO; bpy is 2,2'-bipyridine, and 4-ampy is 4-aminopyridine). Solutions of these two components demonstrated concentration-dependent quenching of the QD photoluminescence (PL) as well as photoinduced release of NO from Ru-NO when irradiated by 530 nm light. A NO release enhancement of ∼8 times resulting from this association was observed under longer wavelength excitation in visible light range. The dynamics of the quenching determined by both PL and transient absorption measurements were probed by ultrafast flash photolysis. A charge transfer mechanism is proposed to explain the quenching of the QD excited states as well as the photosensitized release of NO from Ru-NO.

Effect of silver vanadate on the antibiofilm, adhesion and biocompatibility properties of denture adhesive.

Aim: To evaluate the biological and mechanical properties of an adhesive with nanostructured silver vanadate (AgVO3). Materials & methods: Specimens in poly(methyl methacrylate) (PMMA) were treated with Ultra Corega Cream (UCCA) denture adhesive with or without AgVO3. Biofilms of Candida albicans, Candida glabrata and Streptococcus mutans were grown and the viable cells counted. Fluorescence microscopy was used. The viability of the VERO cell and adhesive strength were evaluated. Results: All concentrations of AgVO3 reduced the biofilm formation and showed no cytotoxic effect. At 5 min and 24 h, UCCA with 5 and 10% AgVO3 showed better performance, respectively. Conclusion: AgVO3 promoted the antibiofilm activity of the adhesive, with a positive effect on the adhesive strength, and was biocompatible.

What is this summary about? Some people wear false teeth called dentures. They use a special glue to keep these false teeth in their mouths. It is important to clean dentures well and remove the glue every day. If the dentures get dirty, they can cause infections of the gums. Doctors and dentists can help, but sometimes medicines do not work well. This study checked to see whether adding a medicine that can kill bacteria into the glue could stop gum swelling and other illnesses, or make them better. What were the results? The glue containing the medicine killed microbes like fungi and bacteria. It also stuck things together well and was safe to use. What do the results mean? Using this special glue could help people with dentures to avoid illness.

Cytotoxic and genotoxic effects in human gingival fibroblast and ions release of endodontic sealers incorporated with nanostructured silver vanadate.

The cytotoxic and genotoxic effects of commercial endodontic sealers (AH Plus, Sealer 26 and Endomethasone N) incorporated with nanostructured silver vanadate decorated with silver nanoparticles (AgVO3 - at concentrations 2.5, 5, and 10%) on human gingival fibroblast (HGF), and the silver (Ag+ ) and vanadium (V4+ /V5+ ) ions release were evaluated. Cytotoxicity, cell death, and genotoxicity tests were carried out with extract samples of 24-hr and 7-days. The release of Ag+ and V4+ /V5+ was evaluated. Cytotoxicity in HGF was caused by AH Plus (AP) with 5 and 10% of AgVO3 (83.84 and 67.49% cell viability, respectively) with 24-hr extract (p < 0.05), as well as all concentrations of AP with 7-days extract (p < 0.05 -AP 0% = 73.17%; AP 2.5% = 75.07%; AP 5% = 70.62%; AP 10% = 68.46% cell viability). The commercial sealers Sealer 26 (S26) and Endomethasone N (EN) were cytotoxic (p < 0.05 - S26 0% = 34.81%; EN 0% = 20.99% cell viability with 7-days extract). AP 10% with 7-days extract induced 32% apoptotic cells in HGF (p < 0.05). Genotoxic effect was not observed. The AP groups released more Ag+ , while S26 and EN released more V4+ /V5+ in 24 hr. The Ag+ can be cytotoxic. In conclusion, the cytotoxicity caused to HGF can be attributed by the commercial sealers and enhanced by incorporation of AgVO3 , was not observed genotoxic effect, and apoptosis was induced only by AH Plus 10% 7-days extract. Ag+ can influence cell viability.

Exciton, Biexciton, and Hot Exciton Dynamics in CsPbBr3 Colloidal Nanoplatelets.

Lead halide perovskites have emerged as promising materials for light-emitting devices. Here, we report the preparation of colloidal CsPbBr3 nanoplatelets (3 × 4 × 23 nm3) experiencing a strong quasi-one-dimensional quantum confinement. Ultrafast transient absorption and broadband fluorescence up-conversion spectroscopies were employed to scrutinize the carrier and quasiparticle dynamics and to obtain a full description of the spectroscopic properties of the material. An exciton binding energy of 350 meV, an absorption cross section at 3.2 eV of 5.0 ± 0.3 × 10-15 cm-2, an efficient biexciton Auger recombination lifetime of 9 ± 1 ps, and a biexciton binding energy of 74 ± 4 meV were determined. Moreover, a short-lived emission from hot excitons was observed, which is related to the formation of band-edge excitons. The time constant of both processes is 300 ± 50 fs. These results show that CsPbBr3 nanoplatelets are indeed quite promising for light-emitting technological applications.

Hydrothermal Synthesis of Aqueous-Soluble Copper Indium Sulfide Nanocrystals and Their Use in Quantum Dot Sensitized Solar Cells.

A facile hydrothermal method to synthesize water-soluble copper indium sulfide (CIS) nanocrystals (NCs) at 150 °C is presented. The obtained samples exhibited three distinct photoluminescence peaks in the red, green and blue spectral regions, corresponding to three size fractions, which could be separated by means of size-selective precipitation. While the red and green emitting fractions consist of 4.5 and 2.5 nm CIS NCs, the blue fraction was identified as in situ formed carbon nanodots showing excitation wavelength dependent emission. When used as light absorbers in quantum dot sensitized solar cells, the individual green and red fractions yielded power conversion efficiencies of 2.9% and 2.6%, respectively. With the unfractionated samples, the efficiency values approaching 5% were obtained. This improvement was mainly due to a significantly enhanced photocurrent arising from complementary panchromatic absorption.

Ligand induced switching of the band alignment in aqueous synthesized CdTe/CdS core/shell nanocrystals.

CdTe/CdS core/shell quantum dots (QDs) are formed in aqueous synthesis via the partial decomposition of hydrophilic thiols, used as surface ligands. In this work, we investigate the influence of the chemical nature (functional group and chain length) of the used surface ligands on the shell formation. Four different surface ligands are compared: 3-mercaptopropionic acid, MPA, thioglycolic acid, TGA, sodium 3-mercaptopropanesulfonate, MPS, and sodium 2-mercaptoethanesulfonate, MES. The QD growth rate increases when the ligand aliphatic chain length decreases due to steric reasons. At the same time, the QDs stabilized with carboxylate ligands grow faster and achieve higher photoluminescence quantum yields compared to those containing sulfonate ligands. The average PL lifetime of TGA and MPA capped QDs is similar (≈20 ns) while in the case of MPS shorter (≈15 ns) and for MES significantly longer (≈30 ns) values are measured. A detailed structural analysis combining powder X-ray diffraction, and X-ray photoelectron spectroscopy (XPS) indicates the existence of two novel regimes of band alignment: in the case of the mercaptocarboxylate ligands the classic type I band alignment between the core and shell materials is predominant, while the mercaptosulfonate ligands induce a quasi-type II alignment (MES) or an inverted type I alignment (MPS). Finally, the effect of the pH value on the optical properties was evaluated: using a ligand excess in solution allows achieving better stability of the QDs while maintaining high photoluminescence intensity at low pH.

Evaluation of antibiofilm and mechanical properties of new nanocomposites based on acrylic resins and silver vanadate nanoparticles.

OBJECTIVE: The purpose of this study was evaluate, for the first time, the impact of incorporation of nanostructured silver vanadate (ß-AgVO3) in antibiofilm and mechanical properties of dental acrylic resins (poly(methyl methacrylate), PMMA). DESIGN: The ß-AgVO3 was synthesized and characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy, and microanalysis (SEM/EDS). Resins specimens were prepared with 0-10% wt.% ß-AgVO3 and characterized by SEM, XRD and optical microscopy. The antibiofim activity of the samples against Candida albicans and Streptococcus mutans was investigated by XTT reduction test, colony-forming units (CFUs), and confocal laser scanning microscopy (CLSM). The flexural strength, hardness, and surface roughness of the samples containing ß-AgVO3 were compared with the pure PMMA matrix. RESULTS: The incorporation of 10% ß-AgVO3 significantly reduced the metabolic activity of C. albicans and S. mutans (p<0.05). There was a reduction in microbial load (CFU/mL) of microorganisms for the different concentrations used (p<0.05), which was confirmed by confocal microscopy. The addition of ß-AgVO3 did not change the mechanical properties of hardness and surface roughness of the resins (p>0.05). However, flexural strength decreased with the addition of amounts greater than 1% (p<0.05). CONCLUSIONS: ß-AgVO3 additions in dental acrylic resin may have an impact on inhibition of biofilm of main microorganisms associated with dental prostheses. However, the viability of clinical use should be evaluated in function of changed promoted in some mechanical properties.

Effect of surface ligands on the optical properties of aqueous soluble CdTe quantum dots.

We investigate systematically the influence of the nature of thiol-type capping ligands on the optical and structural properties of highly luminescent CdTe quantum dots synthesized in aqueous media, comparing mercaptopropionic acid (MPA), thioglycolic acid (TGA), 1-thioglycerol (TGH), and glutathione (GSH). The growth rate, size distribution, and quantum yield strongly depend on the type of surface ligand used. While TGH binds too strongly to the nanocrystal surface inhibiting growth, the use of GSH results in the fastest growth kinetics. TGA and MPA show intermediate growth kinetics, but MPA yields a much lower initial size distribution than TGA. The obtained fluorescence quantum yields range from 38% to 73%. XPS studies unambiguously put into evidence the formation of a CdS shell on the CdTe core due to the thermal decomposition of the capping ligands. This shell is thicker when GSH is used as ligand, as compared with TGA ligands.