Jefferson Luis Ferrari

Generation of wide color gamut visible light in rare-earth triply doped tantalum oxide crystalline ceramic powders

Multicolor visible light emitting near-infrared (NIR)-excited Tm/Ho/Yb-codoped tantalum oxide nanopowders were produced using the sol-gel method. The generation of wide color gamut fluorescence in glass-ceramic with orthorhombic Ta2O5 nanocrystals dispersed into amorphous silica-based matrix is observed. The light emission spectroscopic properties of the rare-earth doped SiO2:Ta2O5 nanocomposites as a function of the tantalum content and temperature of annealing is examined. Simultaneously emitted multicolor fluorescence consisting of blue (480 nm), green (540 nm), and red (650 nm) upconversion signals in the SiO2:Ta2O5 system doped with holmium and thulium and sensitized with ytterbium, is demonstrated. It is also demonstrated that the proper choice of the rare-earth content and the NIR excitation power yielded the generation and control of the three primary colors and allows the emission of a balanced white overall luminescence from the glass-ceramic nanopowder samples.

Influence of Inert and Oxidizing Atmospheres on the Physical and Optical Properties of Luminescent Carbon Dots Prepared through Pyrolysis of a Model Molecule

This work used L-tartaric acid as a model molecule to evaluate how the use of inert and oxidizing atmospheres during pyrolysis affected the physical and optical properties of the resulting carbon dots (CDs). Pyrolysis revealed to be a simple procedure that afforded CDs in a single step, dismissed the addition of organic solvents, and involved only one extraction stage that employed water. By X-ray diffraction a dependency between the structure of the CDs and the atmosphere (oxidizing or inert) used during the pyrolysis was found. Potentiometric titration demonstrated that the CDs were largely soluble in water; it also aided characterization of the various groups that contained sp(3) -hybridized carbon atoms on the surface of the dots. Raman spectroscopy suggested that different amounts of sp(2)- and sp(3)-hybridized carbon atoms emerged on the CDs depending on the pyrolysis atmosphere. In conclusion, the pyrolysis atmosphere influenced the physical properties, such as the composition and the final structure.

Carbon Quantum Dots: Chemical Synthesis, Properties and Applications

Carbon quantum dots (CQDs) were accidentally discovered in 2004, and since then have attracted considerable research interest due to their unique properties and potential technological applications. In addition to the excellent biocompatibility, their properties confer controlling the emission of light and multiphoton absorption, which can be potentially used in materials for light emitting devices (LEDs), solar photovoltaic devices, for photocatalytic degradation of dye molecules and also bioimagens and detection as nanoprobes. With nearly ten years of development, considerable progress has been made in methods for synthesizing CQDs and in the understanding of their properties. This review describes the main chemical methods used for their obtention, the investigation of their properties together with their most important technological applications.

PREPARAÇÃO DE PONTOS DE CARBONO E SUA CARACTERIZAÇÃO ÓPTICA: UM EXPERIMENTO PARA INTRODUZIR NANOCIÊNCIA NA GRADUAÇÃO

Carbon dots (CDs) constitute a new class of carbon-based nanomaterials that measure less than 10 nm and display attractive physical and chemical features such as fluorescence. CDs have been considered the new “power” carbon nanomaterials since their accidental discovery in 2004. This study reports a simple, easy, and accessible experiment for undergraduate courses. The experiment involves the preparation of CDs by pyrolysis using commercial gelatin as a low cost precursor as well as CD purification and optical characterization. The optical properties of CDs such as absorption and emission properties make them a promising material for teaching the basic concepts and techniques used for characterization of nanomaterials. Also, the reactants and final product are suitable for undergraduate courses since they are non-toxic materials. The prepared CDs can be used in such applications as bioimaging, solar cells, and photocatalysis.

Thermal, Structural and Crystallization Study of Niobium Potassium Phosphate Glasses

New glass compositions were investigated in the binary system KPO3-Nb2O5. The glass forming domain was determined by melt-quenching of the starting nominal compositions and it has been experimentally observed that glass samples can be obtained between the molar compositions 95KPO3-5Nb2O5 and 50KPO3-50Nb2O5. Chemically stable compositions from 80KPO3-20Nb2O5 to 50KPO3-50Nb2O5 were characterized by DSC for determination of characteristic temperatures Tg, Tx, Tp and Tf. Glass transition temperatures strongly increase with Nb2O5 content whereas thermal stability against devitrification progressively decreases. Thermal data were used to suggest a structural model in which NbOx polyhedra are inserted inside the phosphate chains of PO4 units. For higher Nb2O5 contents, NbOx units progressively link together to form amorphous NbOx clusters, responsible for the yellow color and lower thermal stability against devitrification. For the composition 50KPO3-50Nb2O5, it has been found that the first crystallization peak is related with precipitation of hexagonal Nb2O5 in the glass matrix whereas the high temperature exothermic peak is due to both phase transition of hexagonal niobium oxide to monoclinic niobium oxide and precipitation of niobium potassium phosphate K2Nb6P4O26.

Generation of wide color gamut visible light in NIR-excited thulium-holmium-ytterbium codoped tantalum oxide nanopowders

Multicolor visible light emitting NIR-excited Tm/Ho/Yb-codoped tantalum oxide nanopowders were produced using the sol-gel method. The generation of wide color gamut fluorescence in glass-ceramic with orthorhombic Ta2O5 nanocrystals dispersed into amorphous silica-based matrix is observed. The light emission spectroscopic properties of the rare-earth doped SiO2:Ta2O5 nanocomposites as a function of the tantalum content and temperature of annealing is examined. Simultaneously emitted multicolor fluorescence consisting of blue(480 nm), green(540 nm) and red(650 nm) upconversion signals in the SiO2:Ta2O5 system doped with holmium and thulium and sensitized with ytterbium, is demonstrated. It is also demonstrated that the proper choice of the rare-earth content and the NIR excitation power yielded the generation and control of the three primary colors and allows the emission of a balanced white overall luminescence from the glass-ceramic nanopowder samples.

Synthesis of multicolor photoluminescent carbon quantum dots functionalized with hydrocarbons of different chain lengths

Abstract We report the synthesis of novel multicolor photoluminescent carbon quantum dots (CQDs) from multi-wall carbon nanotubes, and their covalent functionalization with amines by peptide bonds. The resulting CQDs consisted of quasi-spherical graphite nanocrystals around 10 nm diameter, which were capped by amines with different hydrocarbon chains such as propylamine, octylamine, dodecylamine and octadecylamine. The introduction of nitrogen atoms and the hydrocarbon chains in the surface of the CQDs dramatically affected their photoluminescence profiles, quantum yields and solubility. The photoluminescence emission wavelength of these novel organic-soluble CQDs depended on the excitation wavelength and their quantum yields varied with the chain length of the hydrocarbon chain attached to the surface of the carbon dots.

Synthesis and Optical Properties of Water-Soluble CdTe:Zn2+ Quantum Dots Prepared by the One-Pot Approach

Fluorescence quantum yield (FQY) for CdTe:Zn 2+ QDs were determined by the method presented by Horiba 1 using rhodamine 6G (QY = 0.95) as standard sample. Briefly, rhodamine 6G stock solution was prepared dissolving 4.8 × 10 -3 mmol in 50 mL of water. Different aliquots of this solution were pipetted into a volumetric flask and then the volume was measured with deionized water to 10 mL so that the optical density of the solution was in the range of 0.01 to 0.001, according to Maître and co-workers. 2 To obtain the standard curve, the solutions had their optical density (OD) and integrated fluorescence band intensity (IFBI) values recorded at the wavelength of 355 nm. With the ordered pairs (DO, IFBI), the linear regression method was applied, obtaining the angular coefficient (Grad) of the curve. After performing the same procedure to CdTe:Zn 2+ quantum dots, the equation 1 was applied.

Photoluminescence and structural analysis of Er3+/Yb3+/Tm3+ triply doped Gd2O3

Spectroscopic and structural properties of Er 3+ :Yb 3+ :Tm 3+ triply doped Gd 2 O 3 nanocrystals were investigated. Materiais were heat treated at 800, 900, 1000 and 1100 oC for 4h, and heat treatment effect in the luminescence was discussed. The doping process with RE 3+ was effective on Gd 2 O 3 cubic phase, and structural parameters were determined for this phase. The morphology of the particles did not showed difference on shape and size, demonstrating the reproducibility of the synthesis methods. The luminescence at visible and infrared regions was studied when samples are excited at 980 nm. Materials present intense visible up-conversion and infrared emissions at 1550 nm, and Er 3+ emissions are favored in the materials, concluding that in Er 3+ :Yb 3+ :Tm 3+ triply doped materials the transfer between Yb 3+ and Er 3+ occurs preferentially. Materials due absorption at UV and IR regions can be availed in solar concentrators, as well as 1550nm for optical telecom applications in the C-band.

The Role that Electrolytes Play in the Synthesis of Water-Soluble CdTe Quantum Dots Prepared at Ambient Temperature

In this work, we have synthesized CdTe quantum dots (QDs) dispersed in an aqueous medium at ambient temperature, and investigated their optical properties. Synthesis of CdTe QDs in the presence of simple amines removed the need for an additional energy source and inert atmosphere, in a simple and inexpensive experimental setup. The use of ammonia or hydrazine promoted nanoparticle growth by kinetic nanocrystal agglomeration in the initial growth stage. These weak electrolytes acted in the electrical double layer during the growth of the nanocrystals. A comparative study on the concentration of hydrazine in the reaction medium helped to investigate their role in nanocrystal growth. Substitution of hydrazine for ethylenediamine and other electrolytes like sodium chloride and ammonium chloride contributed to a better understanding of the mechanism that underlies the use of primary amines in the synthesis of CdTe. The synthesis conditions afforded the highest photoluminescence quantum yield for CdTe QDs prepared at room temperature (27.5%).