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61.
Artizzu F Deplano P Marchiò L Mercuri ML Pilia L Serpe A Quochi F Orrù R Cordella F Meinardi F Tubino R Mura A Bongiovanni G 《Inorganic chemistry》2005,44(4):840-842
We report the first combined optical and structural investigation of the water free Er-quinolinolate complex, an organo-lanthanide system of interest for 1.5-microm telecom applications. Structural data demonstrate that the complex has a trinuclear structure (Er3Q9) which provides the Er metals with an octa-coordination by the organic ligand and prevents solvent and water molecules from entering the lanthanide coordination sphere. The results of the structural analysis allow us to infer that the strong Er luminescence quenching exhibited by the Er3Q9 complex is due uniquely to resonant energy transfer to the aromatic C-H vibrations of the ligand, providing the correct tools to design more efficient emitters. 相似文献
62.
63.
Mariana Mandelli de Almeida Nádia Araci Bou-Chacra Cibele Rosana Ribeiro de Castro Lima Jivaldo do Rosário Matos Elder Moscardini Filho Lucildes Pita Mercuri André Rolim Baby Telma Mary Kaneko Maria Valéria Robles Velasco 《Journal of Thermal Analysis and Calorimetry》2014,115(3):2401-2406
The ursolic acid (UA) increases the skin’s barrier function and acts in epidermal differentiation of keratinocytes in the epidermis, promoting cell renewal. Besides the mentioned properties UA also has antioxidant, antimicrobial, and anti-irritant functions to cosmetic formulations. Thus, it is necessary formulation studies to insure the development of quality cosmetic products containing this active, increasing its antioxidant potential within nanoparticles. This study aims to characterize and evaluate the thermal behavior of UA in free and nanostructured forms, and both incorporated into a cosmetic base formulation, using thermogravimetry and differential scanning calorimetry. Through the study were observed that free UA, in the embedded nanoparticles and in base formulation exhibited different behavior in similar thermal profile and relative to the presence of UA. The UA remained stable to a temperature of 250 °C and the technique has been shown to be effective for characterizing UA, evaluate water content, and stability of the formulation base. 相似文献
64.
65.
We present a method to align liquid crystal (LC) samples in their SmecticA phase, useful to obtain permanent homeotropic single domains even in compounds where the nematic phase is absent. It is based on the application of a strain field, within the sample volume, which tends to align the molecules all towards a common direction. The study was carried out in samples of 4-decyl-4′-cyanobiphenyl (10CB), 4-octyl-4′-cyanobiphenyl (8CB) and n-hexyl-4′-n-pentyloxy biphenyl-4-carboxylate (65OBC) LCs, and the alignment efficiency was monitored by polarisation microscopy observations and by thermal diffusivity measurements. 相似文献
66.
W.X. Que Y. Zhou Y.L. Lam C.H. Kam J. Zhou K. Pita Y.C. Chan S. Buddhudu L.H. Gan G.R. Deen 《Applied Physics A: Materials Science & Processing》2001,73(4):485-488
Neodymium (III) oxide nanocrystal/titania/organically-modified silane (ormosil) composite thin films have been prepared using
a chemical approach consisting of a combination of inverse microemulsion and sol-gel techniques at low temperature. Transmission
electron microscopy shows that the neodymium (III) oxide nanoparticles have a needle-like nanocrystal structure. A strong
room temperature emission at 1064 nm, corresponding to the 4
F
3/2?4
I
11/2 transition, has been observed as a function of the heat treatment temperature used for the production of the composite thin
films. In addition to this emission, two other main emissions at 890 nm and at 1336 nm have also been observed. In particular,
there was a clear shoulder peak at 1145 nm, probably be due to the host matrix, which was observed in all the measured samples
and this shoulder peak gave a maximum intensity after heat treatment at 300 °C.
Received: 6 September 2000 / Accepted: 15 November 2000 / Published online: 20 June 2001 相似文献
67.
W. Que Y. Zhou Y.L. Lam K. Pita Y.C. Chan C.H. Kam 《Applied Physics A: Materials Science & Processing》2001,73(2):209-213
Luminescence properties from erbium (III) oxide nanocrystals dispersed in titania/organically modified silane composite thin
films were studied. Erbium oxide nanocrystals were prepared by an inverse microemulsion technique. A strong room-temperature
photoluminescence was observed at 1.531 μm, with the full width at half maximum (FWHM) of 22 nm due to intra-atomic transitions
between 4
I
13/2 and 4
I
15/2 levels in the erbium (III) ion. The shape, peak position, and FWHM of the photoluminescence signals from the composite thin
films were quite comparable to those prepared by other methods. The photoluminescence peak of the composite thin films showed
a maximum intensity at the heat-treatment temperature of 300 °C. A room-temperature green up-conversion emission at 543 nm
(4
S
3/2?4
I
15/2) was observed for the composite thin films with different heat-treatment temperatures upon excitation at 993 nm. The up-conversion
emission mechanism was explained by means of an energy-level diagram and the lifetime of the visible up-conversion emission
was measured.
Received: 10 July 2000 / Accepted: 11 July 2000 / Published online: 5 October 2000 相似文献
68.
In this work a simple technique to extract the texture function in granular thin film media is implemented. The technique is based on previous work in which the distribution function of particles easy axes f(α) is calculated from the measured parallel remanence curve (Mrp(β)). In this simple technique we consider that the measured Mrp(β) curve can be fitted to a series of cos(2β), i.e. Mrp(β)=B0+B2 cos(2β)+B4 cos(4β) where the angle β is the angle by which the film is rotated. This approximation is found to be valid when the texture function has a standard deviation >20°. On this basis, the constants B0, B2 and B4 can be determined by using only three data points for the parallel remanence, Mrp(0), Mrp(45°) and Mrp(90°). The new technique is applied to a textured thin film consisting of cobalt ferrite particles 17 nm in diameter and to a commercial Sony video tape. Using this simple technique, the obtained texture functions are found to be similar to those obtained from the full Mrp(β) curves. This new technique will furnish a simple method with which the texture function in 2D systems can be obtained. 相似文献
69.
Marcos Pita Jan Halámek Soujanya Chinnapareddy Donald J. White Vladimir Gartstein Evgeny Katz 《Electroanalysis》2012,24(5):1033-1038
Electrochemical Faradaic impedance spectroscopy was applied to evaluate dependence of the electrical resistance on human teeth. The experiments were performed using iodide anions as a redox probe to model permeability of teeth for fluoride upon an iontophoresis process. Tooth molars were used – as these are teeth most affected by tooth decay processes in vivo. Teeth compared included sound molars – with no evidence of pit and fissure decay, teeth with pits and fissures regarded ‘clinically’ as showing signs of decay, and teeth with crowns removed to present exposed dentin surfaces. A difference of more than an order of magnitude in electrical resistance was observed between sound molars and those regarded as showing evidence of tooth decay processes. Sound dentin, as expected from structural considerations demonstrated significantly lower resistance when compared to sound molars. Importantly, the difference in tooth resistance measured between carious and sound molars was shown to be much more representative of their structural integrity than comparison of digitally processed images of the teeth. The results support the utility of electrochemical Faradaic impedance spectroscopy for the development of understanding on how tooth electrical resistance may vary according to structural changes. This understanding may be useful to continued refinements in the use of electrical resistance measures as caries diagnostics and support generically the potential for iontophoretic processes in in‐office fluoride treatments of teeth. 相似文献
70.
Silvia Bruni Vittoria Guglielmi Federica Pozzi Anna Maria Mercuri 《Journal of Raman spectroscopy : JRS》2011,42(3):465-473
The effectiveness of surface‐enhanced Raman spectroscopy (SERS) spectrocsopy on Ag colloids has been successfully demonstrated for the identification of a yellow dye in two ancient wool threads found in the Royal Tumulus of In Aghelachem, Libyan Sahara, belonging to the Garamantian period (2nd–3rd century A.D.). High‐performance liquid chromatography (HPLC) highlighted the presence of ellagic acid in the extracts from the threads, excluding other chromophores. This result, together with the abundance of malic acid detected by gas chromatography‐mass spectrometry (GC‐MS), suggested the possible use of pomegranate rind or sumac berries as source of the yellow dye, both plants being documented in the Fezzan area during the Garamantian period. HPLC analyses and SERS spectra acquired on the extracts of the ancient threads were therefore compared with those obtained from pomegranate and sumac extracts of the corresponding fruits and reference dyed wool samples, allowing us to identify the yellow dye as deriving from pomegranate (Punica granatum L.). SERS spectra of ellagic acid and dyes extracted from pomegranate rind and sumac berries are reported here for the first time. A methodological improvement is also presented, based on the use of NaClO4 as aggregating agent, that leads to a significant increase of the signal‐to‐noise ratio in the SERS spectra. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献