Fluorescence quantum efficiency of CdSe/CdS magic-sized quantum dots functionalized with carboxyl or hydroxyl groups

AbstractThe present letter reports the thermo-optical properties of functionalized CdSe/CdS magic-sized quantum dots (MSQDs) (sizes 1.9–2.3nm) with carboxyl (R–COOH) or hydroxyl (R–OH) groups in aqueous solutions. Atomic force microscopy and infrared transmittance measurements were used to determine the size of the QDs and to highlight the functionalized groups. Absolute nonradiative quantum efficiency (φ) and radiative quantum efficiency (η) values were determined by applying two techniques: thermal lens (TL) and an alternative method that analyzes the ring patterns generated in a laser beam due to thermally induced self-phase-modulation effects known as the conical diffraction. Fluorescence measurements corroborate the TL results

Diluted Magnetic Semiconductors Nanocrystals: Saturation and Modulation

Diluted Magnetic Semiconductor (DMS) nanocrystals are a new class of materials formed by doping the semiconductor with transition metals (TM), which gives interesting magneto-optical properties. These properties are attributed to the exchange interaction between the pure semiconductor’s sp-electrons and the localized TM d-electrons. This book chapter shows exciting results of new DMS developed by the group, both in powder form and embedded in glassy systems. Depending on the concentration of doping ions, saturation of the incorporation of substitutional and interstitial sites in the nanocrystal structure may occur, forming other nanocrystals. In this context, we investigated the doping saturation limit in nanopowders of DMS Zn1-xMnxO NCs and Zn1-xMnxTe, Zn0.99-xMn0.01CoxTe, and Bi2-xCoxS NCs synthesized in glassy matrices. Thus, the sites’ saturation into the crystalline lattice of nanocrystals is a topic little reported in the literature, and we will comment on this work. Therefore, we will show results from the group about the modulation and saturation in diluted magnetic semiconductors nanocrystals in this work

Doped Semiconductor Nanocrystals: Development and Applications

This chapter aims to show significant progress that our group has been developing and the applications of several doped semiconductor nanocrystals (NCs), as nanopowders or embedded in glass systems. Depending on the type of dopant incorporated in the nanocrystals, the physical, chemical, and biological properties can be intensified. However, it can also generate undesired toxic effects that can potentially compromise its use. Here we present the potential of zinc oxide NCs doped with silver (Ag), gold (Au), and magnesium (Mg) ions to control bacterial diseases in agriculture. We have also performed biocompatibility analysis of the pure and Ag-doped sodium titanate (Na2Ti3O7) NCs in Drosophila. The doped nanocrystals embedded in glassy systems are chrome (Cr) or copper (Cu) in ZnTe and Bi2Te3 NCs for spintronic development nanodevices. Therefore, we will show several advantages that doped nanocrystals may present in the technological and biotechnological areas

Sensor Surface Design with NanoMaterials: A New Platform in the Diagnosis of COVID-19

Mass testing for COVID-19 is essential to defining patient management strategies, choosing the best clinical management, and dimensioning strategies for controlling viral dissemination and immunization strategies. Thus, it is of utmost importance to search for devices that allow a quick and reliable diagnosis of low cost that can be transposed from the bench to the bedside, such as biosensors. These devices can help choose the correct clinical management to minimize factors that lead to infected patients developing more severe diseases. The use of nanomaterials to modify biosensors’ surfaces to increase these devices’ sensitivity and their biofunctionality enables high-quality nanotechnological platforms. In addition to the diagnostic benefits, nanotechnological platforms that facilitate the monitoring of anti-SARS-CoV-2 antibodies may be the key to determining loss of protective immune response after an episode of COVID-19, which leads to a possible chance of reinfection, as well as how they can be used to assess and monitor the success of immunization strategies, which are beginning to be administered on a large scale and that the extent and duration of their protection will need to be determined. Therefore, in this chapter, we will cover nanomaterials’ use and their functionalities in the surface design of sensors, thus generating nanotechnological platforms in the various facets of the diagnosis of COVID-19

Transition Metals Doped Nanocrystals: Synthesis, Characterization, and Applications

Doping is a technique that makes it possible to incorporate substitutional ions into the crystalline structure of materials, generating exciting properties. This book chapter will comment on the transition metals (TM) doped nanocrystals (NCs) and how doping and concentration influence applications and biocompatibility. In the NCs doped with TM, there is a strong interaction of sp-d exchange between the NCs’ charge carriers and the unpaired electrons of the MT, generating new and exciting properties. These doped NCs can be nanopowders or be embedded in glass matrices, depending on the application of interest. Therefore, we show the group results of synthesis, characterization, and applications of iron or copper-doped ZnO nanopowders and chromium-doped Bi2S3, nickel-doped ZnTe, and manganese-doped CdTe quantum dots in the glass matrices

Study of optical properties of borosilicate glass doped with Ytterbium as a function of the concentration

Rare Earth elements have been studied for different scientific areas due to its excellent spectroscopic and magnetic properties with possible application for construction of different optical and electric devices (MARTINS, 2005; LOURENÇO et al., 2011). In this work, it is studied the optical properties of Ytterbium (Yb3+) ions embedded in a lead-borosilicate glass matrix synthesized by the melting method, using the optical absorption and photoluminescence techniques. The Yb3+ ions were chosen to dope the glass matrix because it has an energy level scheme more simplified compared with other Rare-Earth ions, with only two energy levels, making it very attractive for the construction of high efficiency optical devices. Increasing the annealing temperature as well as the ion concentration in the matrix leads to a shift of the optical band gap of the matrix to higher energies. We believe that this shift (blue-shift) can be associated with the nanocrystallization process of the glass matrix SBP (SiO2, B2O3, PbO2). The reduction of radiative lifetime with increasing ion concentration in matrix was studied using the Stokowski empirical relation, in which, it studies processes of energy transfer as a function of Rare-Earth concentration.</p

Formação e caracterização óptica de filmes automontados de POMA/PPV Formation and optical characterization of POMA/PPV self-assembly films

<abstract language="eng">A study is presented of the formation and optical properties of polymeric heterostructures from poly(p-phenylene vinylene) (PPV) and poly(o-methoxyaniline) (POMA) produced via the self-assembly technique. POMA layers were obtained in a non self-limiting process from its emeraldine salt, semiconducting form in HCl solution. Thermal conversion of PPV was performed at low temperatures with the substitution of the counter-ion Cl in the PPV precursor by a long sulfonic chain, the dodecylbenzenesulfonate (DBS) ion. The optical properties of PPV films converted in this way are not affected by POMA, which can be used as transparent electrode of PPV luminescent devices

Synthesis and Study of Fe-Doped Bi2S3 Semimagnetic Nanocrystals Embedded in a Glass Matrix

Iron-doped bismuth sulphide (Bi2−xFexS3) nanocrystals have been successfully synthesized in a glass matrix using the fusion method. Transmission electron microscopy images and energy dispersive spectroscopy data clearly show that nanocrystals are formed with an average diameter of 7–9 nm, depending on the thermic treatment time, and contain Fe in their chemical composition. Magnetic force microscopy measurements show magnetic phase contrast patterns, providing further evidence of Fe incorporation in the nanocrystal structure. The electron paramagnetic resonance spectra displayed Fe3+ typical characteristics, with spin of 5/2 in the 3d5 electronic state, thereby confirming the expected trivalent state of Fe ions in the Bi2S3 host structure. Results from the spin polarized density functional theory simulations, for the bulk Fe-doped Bi2S3 counterpart, corroborate the experimental fact that the volume of the unit cell decreases with Fe substitutionally doping at Bi1 and Bi2 sites. The Bader charge analysis indicated a pseudo valency charge of 1.322|e| on FeBi1 and 1.306|e| on FeBi2 ions, and a spin contribution for the magnetic moment of 5.0 µB per unit cell containing one Fe atom. Electronic band structures showed that the (indirect) band gap changes from 1.17 eV for Bi2S3 bulk to 0.71 eV (0.74 eV) for Bi2S3:FeBi1 (Bi2S3:FeBi2). These results are compatible with the 3d5 high-spin state of Fe3+, and are in agreement with the experimental results, within the density functional theory accuracy

Photoluminescence and Magnetism in Mn2+-Doped ZnO Nanostructures Grown Rapidly by the Microwave Hydrothermal Method

Zn1-xMnxO nanostructures were synthesized via the microwave-assisted hydrothermal method, which rapidly produces particles of controlled size and morphology. Samples were analyzed considering the effects of manganese ion concentration. XRD revealed that all samples had wurtzite-type structure with Mn2+ ions incorporated in the oxide lattice. UV-vis spectra showed absorption bands from the d-d transitions of Mn2+ ions. As the doping concentration increased, the value of the energy gap decreased, indicating intermediary energy levels within the band gap in the Mn-doped ZnO samples. All samples produced broadband photoluminescence (PL) emissions in the yellow-orange-red range. Additionally, the PL intensity decreased with Mn2+ ion incorporation into the ZnO lattice due to the creation of new recombination centers. Microscopy images showed that manganese in the ZnO matrix produced homogeneously distributed nanostructures. EPR results indicated two locations of Mn2+ ions in the ZnO lattice, lower concentrations in the core of the lattice and higher concentrations at the surface.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG)Rede Nanobiotec/BrasilRede Mineira de Quimica (RQ:MG)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Univ Fed Uberlandia, Inst Quim, BR-38400902 Uberlandia, MG, BrazilUniv Fed Uberlandia, Inst Fis, LNMIS, BR-38400902 Uberlandia, MG, BrazilUniversidade Federal de São Paulo, Dept Ciencias Mar, BR-11030400 Santos, BrazilUniversidade Federal de São Paulo, Dept Ciencias Mar, BR-11030400 Santos, BrazilCNPq: 477150/2008-0FAPEMIG: APQ-01842-09Web of Scienc