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In this work, over the course of four seasons (12 months), we have monitored the fluorescence quantum efficiency (η) from two sets (S1 and S2) of fresh natural dye extracts from the leaves of Tradescantia pallida purpurea. The natural dye was extracted in aqueous solutions from leaves collected from regions with a predominance of shade (S1) and sun (S2) during the day. The thermo-optical parameter fractional thermal load (φ) was measured using conical diffraction (CD) patterns caused by thermally driven self-phase modulation, for η determination in both sets of solutions. Fluorescence measurements corroborate the CD results, and the η values are, on average, slightly higher (~ 11%) in the summer than in the other seasons for both sets of samples (S1 and S2). In addition, the experimental results are presented using natural dye extracted from Tradescantia pallida purpurea as a fungicide probe in Fusarium solani, Sclerotinia sclerotiorum, and Colletotrichum gloeosporioides fungi. The promising fungicide results obtained for the aqueous natural dye extract were compared with those obtained for other natural dyes and fungi. The fungi tested are of the necrotrophic group and constitute important pathosystems in Brazil, causing diseases in several crops that synthetic fungicides often cannot control or do so with low efficiency.

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The present work reports the spectroscopic and thermo-optical properties of CdSe/ZnS and CdSe/CdS core-shell quantum dots (QDs) embedded in synthetic saliva. Spectroscopy studies were performed applying nonfunctionalized CdSe/ZnS QDs (3.4, 3.9 and 5.1 nm cores) and hydroxyl group-functionalized ultrasmall CdSe/CdS core-shell quantum dots (1.6 nm core) suspended in artificial saliva at different potential of hydrogen (pH) values. Saliva was chosen because it is important in a variety of functions such as protecting teeth through the buffering capacity of the formed biofilm, hydration, and dental remineralization. Thermo-optical characterizations using the thermal lens (TL) technique were performed in QD-biofluids for different QD sizes and pH values (3.9-8.3) of the synthetic oral fluids. Transient TL measurements were applied to determine the fluorescence quantum efficiency (η) in QD-biomaterial systems. High η value was obtained for ultrasmall CdSe/CdS QDs. Fluorescence spectral measurements of the biomaterials support the TL results. In addition, for nonfunctionalized (3.4 and 5.1 nm) and hydroxyl group-functionalized QDs, the temporal behavior of the fluorescence spectra was accomplished about approximately 1200 h at two different biofluid pH values (3.9 and 8.3). The temporal fluorescence intensity result is dependent on the pH of the saliva in which the QDs were embedded, QD functionalization and QD sizes. The time for an approximately 50% decrease in the peak intensity fluorescence of CdSe/ZnS QDs (3.4 nm core) and ultrasmall CdSe/CdS QDs is respectively 25 h and 312 h at pH 3.9 and 48 h and 360 h at pH 8.3.

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Thermal lens spectroscopy (TLS), differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) techniques were applied to the thermo-optical property analysis of a new phosphate glass matrix PANK with nominal composition 40P2O5·20Al2O3·35Na2O·5K2O (mol%), doped with different Nd(3+) compositions. This glass system, synthesized by the fusion protocol, presents high transparency from UV to the near infrared, excellent thermo-optical properties at room temperature and high fluorescence quantum efficiency. Thermal lens phase shift parameters, thermal diffusivity and the DSC signal present pronounced changes at about 61 °C for the PANK glass system. This anomalous behavior was associated with a phase transition in the nanostructured glass materials. The FTIR signal confirms the presence of isolated PO4 tetrahedron groups connected to different cations in PANK glass. As a main result, our experimental data suggest that these tetrahedron groups present a structural phase transition, paraelectric-ferroelectric phase transition, similar to that in potassium dihydrogen phosphate, KH2PO4, nanocrystals and which TLS technique can be used as a sensitive method to investigate changes in the structural level of nanostructured materials.

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Cadmium selenide/zinc sulfide (CdSe/ZnS) core-shell quantum dots (QDs) embedded in biocompatible materials were thermally and optically characterized with a thermal lens (TL) technique. Transient TL measurements were performed with a mode-mismatched, dual-beam (excitation and probe) configuration. A thermo-optical study of the CdSe/ZnS QDs was performed for different core diameters (3.5, 4.0, 5.2, and 6.6 nm) in aqueous solution and synthetic saliva, and three different core diameters (2.4, 2.9, and 4.1 nm) embedded in restorative dental resin (0.025% by mass). The thermal diffusivity results are characteristic of the biocompatible matrices. The radiative quantum efficiencies for aqueous solution and biofluid materials are dependent on the core size of the CdSe/ZnS core-shell QDs. The results obtained from the fluorescence spectral measurements for the biocompatible materials support the TL results.

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Nowadays, the synthetic dyes (as erythrosine, ponceau and tartrazina) and natural colourants (as annatto, paprika, curcuma and anthocyanin) are indispensable in the food, pharmaceutical and cosmetics applications. However, the use of natural colourant has been considered safer for human consumption then synthetic dye. For practical applications of the coloring, optical properties are important for the understanding of the characteristics of them. In this work, we presented the absorption and fluorescence spectroscopic characterizations of annatto extracts obtained from the seeds of the tropical shrub Bixa orellana L. solutions and commercial colourant. The measurements were performed in annatto extracts with acetone and chloroform in different concentrations range (3.5-52.5) µg/mL. The main carotenoids detected in annatto seeds is bixin. The numerical calculus of the absorbance spectra for cis- and trans-bixin conformation is presented. In addition, for commercial colourant, the measurements were performed for six different brands and five lots each one. Modifications in the shape of the colorific fluorescence spectra were observed and it can be an indicative of differences in the industrial methods applied for obtaining annatto pigments powders and/or the possibility of the presence of other impurities added in the commercial powders.

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OBJECTIVES: We characterized the optical properties, such as absorbance and fluorescence, of dental resins containing quantum dots (QD). We also determined the doping level needed to obtain a broad and nearly flat emission spectrum that provides the perception of white color. METHODS: The samples studied were resin composites from Charisma (Heraeus Kulzer) prepared with CdSe/ZnS core-shell QD (0.05-0.77 mass%). RESULTS: The results showed that the fluorescence of dental resin composites can be tailored by using CdSe/ZnS core-shell quantum dots. CONCLUSION: QD core incorporation into dental resins allows the fabrication of restorative materials with fluorescence properties that closely match those of natural human teeth.

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Mode-mismatched thermal lens (TL) measurements in Cr3+-doped fluoride crystals (LiSrAIF6 and LiSrGaF6) are reported. A nonlinear increase of the TL signal, and decrease of quantum efficiency, with increasing excitation power was observed and attributed to energy-transfer upconversion (ETU). Assuming an upconversion rate that is proportional to the excited-state population, Wup = gammaN(e), the theoretical model developed fits the experimental data well. The ETU parameters (gamma) were determined with unprecedented accuracy for low Cr concentrations. Thermo-optical parameters (K, ds/dT) were also obtained.