Diogo Alves Gálico

Synthesis, characterization and thermal behavior of solid state of some mefenamate of trivalent lanthanides (La, Ce, Pr and Nd)

Solid-state Ln(Mef)3 compounds, where Ln stands for some trivalent lanthanides (La, Ce, Pr and Nd) and Mef is the mefenamate (C15H14NO2−) ligand, were synthesized. The characterization and thermal and spectroscopic study of the compounds were performed using elemental analysis, complexometry, image analysis by field emission gun, simultaneous thermogravimetry and differential scanning calorimetry coupled to Fourier transform infrared spectroscopy, X-ray diffractometry, near-infrared and mid-infrared spectroscopy. All the analyses showed that the compounds were obtained in the anhydrous state. The thermoanalytical results showed that the stability and thermal behavior were markedly influenced by the atmosphere used. Moreover, the curves show that the thermal decomposition takes place in two or three steps, with the formation of lanthanide oxide (La2O3, CeO2, Pr6O11 and Nd2O3), as the final residue. Furthermore, the theoretical and experimental spectroscopic data suggested the possible modes of coordination of the ligand with the metals. The DR spectra provided information about the ligand absorption bands and the f–f transitions of Nd3+ and Pr3+ ions.

Temperature probing and emission color tuning by morphology and size control of upconverting β-NaYb0.67Gd0.30F4:Tm0.015:Ho0.015 nanoparticles

The chemical composition, shape and size of upconverting nanoparticles are known to have a great influence on their spectroscopic properties, such as the emission color and the emission intensity variation as a function of temperature. This work shows the color tuning and the thermal sensitivity of NaYb0.67Gd0.30F4:Tm0.015:Ho0.015 nanoparticles synthesized by two different approaches of the same synthetic method showing the influence of size and morphology, 250 nm hexagonal-plated and 30 nm spheroidal nanoparticles, on the visible upconversion color under NIR irradiation. According to the 1931-CIE diagram, the hexagonal-shaped nanoparticles show white light emission and the spheroidal ones generate red light emission under 980 nm excitation. Besides, the variation of the luminescence intensity ratio of Tm3+ emissions as a function of temperature was monitored in the 77-293 K temperature range, and the maximum relative sensitivity (Sm) of the samples reached 1.33% K-1 for the hexagonal-plated nanoparticles and 1.76% K-1 for the spheroidal nanoparticles. These maximum sensitivity values are higher compared to the ones found in the literature for temperature sensing using upconverting nanoparticles. These data suggest the versatility of these nanoparticles for applications on white light emission and nanothermometry.

One pot synthesis and systematic study of the photophysical and magnetic properties and thermal sensing of α and β-phase NaLnF4 and β-phase core@shell nanoparticles

In this work we report a modified one-pot thermal decomposition method for the synthesis of NaLnF4 nanoparticles (Ln = Gd, Yb). This modified method allows fine-tuning of the α and β crystalline phases for both light (Gd) and heavy (Yb) lanthanides and also an easy route to the hierarchical nanostructuration of nanoparticles. The core@shell nanostructuration obtained via a step-by-step addition of the shell precursor was demonstrated by HRTEM and STEM/EDS analysis and it greatly improves the upconversion luminescence intensity of the nanoparticles. Under NIR irradiation, the visible Er3+ emission shows high thermal sensitivity in the temperature range of 83 to 323 K, reaching 9.52% K−1 at 83 K for the β-NaGd0.94Pr0.02Er0.02Yb0.02F4@3NaY0.8Yb0.2F4 sample. This is one of the highest values reported so far for upconversion thermal sensing using NaLnF4 nanoparticles. We report for the first time, a comparison between the magnetic properties of α and β-NaGdF4:Pr:Er:Yb nanoparticles. This comparison shows that the α-NaLnF4 samples systematically presented higher magnetization values than the β-NaLnF4. Our work provides a controlled method of synthesis that resulted in NaLnF4 nanoparticles with a high sensitivity for nanothermometry applications at low temperatures. The observed dependence of the magnetic properties on the crystalline phase demonstrated here clearly shows that further studies on the magnetic properties of these fluorides should be encouraged.

High sensitive luminescent ratiometric thermometer based on europium(III) and terbium(III) benzoylacetonate complexes chemically bonded to ethyldiphenylphosphine oxide functionalized polydimethylsiloxane

This work reports on a ratiometric optical temperature probe consisting of a pdms-eddpo(1%)-[Tb0.90Eu0.10(bzac)3](0.25%) membrane where lanthanide(III) complexes are chemically bonded to ethyldiphenylphosphine oxide functionalized polydimethylsiloxane. The ratiometric luminescent temperature probe shows a maximum relative thermal sensitivity of 11.05% K−1 at 203 K, being one of the most sensitive lanthanide systems reported so far. Besides that, the operational range of the ratiometric probe is 158–248 K, where few systems have high sensitivity. Energy transfer is evident from terbium(III) to europium(III) contributing to the high relative thermal sensitivity of the systems. The optical probe is reversible showing a temperature uncertainty smaller than 0.08 K in the operational range.