José A. Fernández

Bio: José A. Fernández is an academic researcher from University of the Basque Country. The author has contributed to research in topics: Photon upconversion & Spectroscopy. The author has an hindex of 32, co-authored 255 publications receiving 4005 citations. Previous affiliations of José A. Fernández include Donostia International Physics Center & Spanish National Research Council.

Profiling and imaging of lipids on brain and liver tissue by matrix-assisted laser desorption/ ionization mass spectrometry using 2-mercaptobenzothiazole as a matrix.

Abstract: 2-Mercaptobenzothiazole (MBT) is employed for the first time as a matrix for the analysis of lipids from tissue extracts using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. We demonstrate that the performance of MBT is superior to that of the matrixes commonly employed for lipids, due to its low vapor pressure, its low acidity, and the formation of small crystals, although because of the strong background at low m/z, it precludes detection of species below approximately 500 Da. This inconvenience can be partly overcome with the formation of Cs adducts. Using a polymer-based dual calibration, a mass accuracy of approximately 10 ppm in lipid extracts and of approximately 80 ppm in tissues is achieved. We present spectra from liver and brain lipid extracts where a large amount of lipid species is identified, in both positive and negative ion modes, with high reproducibility. In addition, the above-mentioned special properties of MBT allow its employment for imaging mass spectrometry. In the present work, images of brain and liver tissues showing different lipid species are presented, demonstrating the advantages of the employment of MBT.

Time-resolved fluorescence-line narrowing and energy-transfer studies in a Eu 3 + -doped fluorophosphate glass

Abstract: The optical properties of ${\mathrm{Eu}}^{3+}$-doped fluorophosphate glasses of composition (in mol %) 60 ${\mathrm{NaPO}}_{3}$-${15\mathrm{B}\mathrm{a}\mathrm{F}}_{2}$-(25-x)${\mathrm{YF}}_{3}$-x${\mathrm{EuF}}_{3}$ (x=0.5, 2, 5, 10, 15, 20, and 25) have been investigated in the 4.2--300 K temperature range by using optical absorption spectroscopy and time-resolved resonant laser-induced fluorescence line narrowing. From the room-temperature absorption spectra Judd-Ofelt parameters have been obtained and used to calculate the spontaneous emission probabilities from the $^{5}$${\mathit{D}}_{0}$ state. The spectral features of the time-resolved fluorescence line-narrowed $^{5}$${\mathit{D}}_{0}$${\ensuremath{\rightarrow}}^{7}$${\mathit{F}}_{0,1}$ emission spectra obtained under resonant excitation at different wavelengths along the $^{7}$${\mathit{F}}_{0}$${\ensuremath{\rightarrow}}^{5}$${\mathit{D}}_{0}$ transition as a function of concentration and temperature reveal the existence of energy migration between discrete regions of the inhomogeneous broadened spectral profile. From the concentration and time dependence of the average rate of excitation transfer, the electronic mechanism ruling the ion-ion interaction can be identified as a dipole-dipole energy transfer process. At low temperatures the average transfer rate parameter slightly depends on wavelength showing a temperature independent behavior. Above 77 K the weak dependence of the transfer rate on excitation wavelength (weak dependence on energy mismatch) together with its T${\mathrm{}}^{3}$ temperature dependence point to a transfer mechanism consistent with a two-site nonresonant two-phonon assisted process. The estimated average crystal field strength grows monotonically with the $^{7}$${\mathit{F}}_{0}$${\ensuremath{\rightarrow}}^{5}$${\mathit{D}}_{0}$ energy suggesting a large variation in the local environment of ${\mathrm{Eu}}^{3+}$ ions in these glasses. The slight increase with concentration of the $^{5}$${\mathit{D}}_{0}$ fluorescence decays together with their single exponential character suggest that the transfer process may be fast enough to drive the system of excited centers to thermal equilibrium. \textcopyright{} 1996 The American Physical Society.

Laser spectroscopy of Nd 3 + ions in GeO 2 − P b O − B i 2 O 3 glasses

Abstract: The optical properties of ${\mathrm{Nd}}^{3+}$ ions in six different compositions of glasses based on ${\mathrm{GeO}}_{2},$ PbO, and ${\mathrm{Bi}}_{2}{\mathrm{O}}_{3}$ have been investigated by using steady-state and time-resolved laser spectroscopy. Judd-Ofelt parameters were derived from the absorption spectra and used to calculate the ${}^{4}{\stackrel{\ensuremath{\rightarrow}}{{F}_{3/2}}}^{4}{I}_{11/2}$ stimulated emission cross section and the ${}^{4}{F}_{3/2}$ radiative lifetime. Site-selective spectroscopy and time resolved fluorescence line narrowing experiments were performed in the ${}^{4}{\stackrel{\ensuremath{\rightarrow}}{{F}_{3/2}}}^{4}{I}_{9/2}{,}^{4}{I}_{11/2}$ transitions. For all samples studied a line narrowing of the ${}^{4}{\stackrel{\ensuremath{\rightarrow}}{{F}_{3/2}}}^{4}{I}_{11/2}$ emission has been observed when exciting at the long wave side of the ${}^{4}{\stackrel{\ensuremath{\rightarrow}}{{I}_{9/2}}}^{4}{F}_{3/2}$ transition. The lifetimes of the ${}^{4}{F}_{3/2}$ state do not show a monotonic variation with the excitation wavelength indicating large site-to-site variations in the local crystal field. Spectral migration of excitation among the ${\mathrm{Nd}}^{3+}$ ions has been studied from the time evolution of the ${}^{4}{\stackrel{\ensuremath{\rightarrow}}{{F}_{3/2}}}^{4}{I}_{9/2}$ spectra under resonant excitation. The results can be interpreted in terms of a dipole-dipole energy transfer mechanism. Visible upconversion has been observed in these glasses under infrared laser excitation.

Ribose Found in the Gas Phase

Abstract: sugar to be detected in the gas phase, isreported by E. J. Cocinero, A. Lesarri, and co-workers in their Communication on page3119 ff. Six conformers were detected by a combination of laser vaporization andmicrowave spectroscopy. All adopt a pyranoside (pyr) structure, stabilized bycooperative hydrogen-bond networks, rather than the furanose form usually found inbiological compounds. This rotational spectrum opens the door to the radio-astronom-ical detection of the first sugar in space.

Matrix-assisted laser desorption ionization imaging mass spectrometry in lipidomics

Abstract: The relevant structural, energetics, and regulatory roles of lipids are universally acknowledged. However, the high variability of lipid species and the large differences in concentrations make unraveling the role played by the different species in metabolism a titanic task. A recently developed technique, known as imaging mass spectrometry, may shed some light on the field, as it enables precise information to be obtained on the location of lipids in tissues. A review of the state of the art of the technique is presented in this manuscript, including detailed analysis of sample-preparation steps, data handling, and the identification of the species mapped so far.

Upconversion and Anti-Stokes Processes with f and d Ions in Solids

Abstract: Before the 1960s, all anti-Stokes emissions, which were known to exist, involved emission energies in excess of excitation energies by only a few kT. They were linked to thermal population of energy states above excitation states by such an energy amount. It was the well-known case of anti-Stokes emission for the so-called thermal bands or in the Raman effect for the well-known anti-Stokes sidebands. Thermoluminescence, where traps are emptied by excitation energies of the order of kT, also constituted a field of anti-Stokes emission of its own. Superexcitation, i.e., raising an already excited electron to an even higher level by excited-state absorption (ESA), was also known but with very weak emissions. These types of well-known anti-Stokes processes have been reviewed in classical textbooks on luminescence.1 All fluorescence light emitters usually follow the well-known principle of the Stokes law which simply states that excitation photons are at a higher energy than emitted ones or, in other words, that output photon energy is weaker than input photon energy. This, in a sense, is an indirect statement that efficiency cannot be larger than 1. This principle is

Principles Of Fluorescence Spectroscopy

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