David Bravo

Unveiling in Vivo Subcutaneous Thermal Dynamics by Infrared Luminescent Nanothermometers

The recent development of core/shell engineering of rare earth doped luminescent nanoparticles has ushered a new era in fluorescence thermal biosensing, allowing for the performance of minimally invasive experiments, not only in living cells but also in more challenging small animal models. Here, the potential use of active-core/active-shell Nd(3+)- and Yb(3+)-doped nanoparticles as subcutaneous thermal probes has been evaluated. These temperature nanoprobes operate in the infrared transparency window of biological tissues, enabling deep temperature sensing into animal bodies thanks to the temperature dependence of their emission spectra that leads to a ratiometric temperature readout. The ability of active-core/active-shell Nd(3+)- and Yb(3+)-doped nanoparticles for unveiling fundamental tissue properties in in vivo conditions was demonstrated by subcutaneous thermal relaxation monitoring through the injected core/shell nanoparticles. The reported results evidence the potential of infrared luminescence nanothermometry as a diagnosis tool at the small animal level.

EPR spectroscopy of Yb3+ in LiNbO3 and Mg:LiNbO3

Abstract Electron paramagnetic resonance (EPR) experiments have been carried out on congruent crystals of LiNbO 3 doped with Yb and crystals codoped with Mg. Crystals without Mg codoping show a complex spectrum which is attributed to slightly different centers of Yb 3+ located at the Li + site. In samples codoped with Mg a new ytterbium spectrum is detected in addition to those observed in crystals without codoping. This new Yb 3+ center is compared to additional centers observed for Er 3+ and trivalent transition metal ions (particularly Cr 3+ ) in LiNbO 3 heavily doped with Mg or Zn. On these grounds the new center can be attributed to Yb 3+ located at the Nb 5+ site of LiNbO 3 .

Induced changes in the refractive index of LiNbO3 crystals through Sc2O3 doping

Abstract The dependence of the ordinary ( n o ) and extraordinary ( n e ) refractive indices in congruent Sc 2 O 3 -doped LiNbO 3 crystals are reported. The Sc 3+ ion concentrations in the crystals were varied from 0% to 7%. It has been found that n o shows a clear singularity for a Sc 3+ ion concentration of 3%. The experimental data of n o and n e are described by a generalised Sellmeier equation, which takes into account different Sc 3+ ions sites location in the host matrix. Additionally, the role of the Sc 2 O 3 content in the intrinsic defect distribution in LiNbO 3 crystals has been studied by using Cr 3+ ions as an EPR probe.

Dose dependence of neutron irradiation effects on MgAl2O4 spinels

The characteristics of the photoluminescence and electron paramagnetic resonance (EPR) spectra of stoichiometric MgAl 2 O 4 spinel specimens irradiated in FFTF-MOTA at temperatures between 385°C and 750°C to fluences ranging from 5.3 to 24.9 x 10 26 nm - 2 are measured. Photoluminescence spectra show a complex behaviour associated with the presence of an active defect with different surroundings. The EPR spectra show two different bands that are associated with different defects.

Shift of the transition temperature in the growth bands of potassium dihydrogen phosphate monitored by electron paramagnetic resonance

The authors have monitored the phase transition of KDP:Cr3+ for growth-band and regular samples (GB and R) by means of EPR, making use of the fact that when the crystal becomes ferroelectric upon cooling, each EPR line splits into two, owing to the presence of two ferroelectric domains. In this way, they have detected an increase in Tc for the GB samples and have interpreted this result according to the model presented by Gonzalo (1989). Also, the model allowed them to estimate the relative distortion of the KDP lattice across the c axis in the GB samples.