Marta Quintanilla

Temperature Sensing with Up-Converting Submicron-Sized LiNbO3:Er3+/Yb3+ Particles

We present the temperature dependence of the green up-converted luminescence in submicron-sized LiNbO3:Er3+/Yb3+ particles in the range between 12 and 180 °C. It is shown that LiNbO3:Er3+/Yb3+ exhibits a very high sensitivity (S = 0.007/°C at physiological temperature and a maximum value of S = 0.014/°C at 350 °C) that surpasses those previously found for other materials based on Er3+/Yb3+ luminescence, indicating that LiNbO3:Er3+/Yb3+ is a suitable probe for optical temperature sensing through the fluorescence intensity ratio technique. This high sensitivity can be explained using the intrinsic spectroscopic parameters of Er3+ ions in this host.

1.3 μm emitting SrF2:Nd3+ nanoparticles for high contrast in vivo imaging in the second biological window

Novel approaches for high contrast, deep tissue, in vivo fluorescence biomedical imaging are based on infrared-emitting nanoparticles working in the so-called second biological window (1,000–1,400 nm). This allows for the acquisition of high resolution, deep tissue images due to the partial transparency of tissues in this particular spectral range. In addition, the optical excitation with low energy (infrared) photons also leads to a drastic reduction in the contribution of autofluorescence to the in vivo image. Nevertheless, as is demonstrated here, working solely in this biological window does not ensure a complete removal of autofluorescence as the specimen’s diet shows a remarkable infrared fluorescence that extends up to 1,100 nm. In this work, we show how the 1,340 nm emission band of Nd3+ ions embedded in SrF2 nanoparticles can be used to produce autofluorescence free, high contrast in vivo fluorescence images. It is also demonstrated that the complete removal of the food-related infrared autofluorescence is imperative for the development of reliable biodistribution studies.

Micro-Raman characterization of Zn-diffused channel waveguides in Tm 3+ :LiNbO 3

In this work micro-Raman scattering experiments have been performed in LiNbO(3):Tm(3+) samples with waveguides fabricated by Zn(2+) in-diffusion. The results shown that Zn(2+) ions enter the lattice in Li(+) sites, but also in interstitial positions. This produces a compaction of the lattice close to the surface of the sample, generating the waveguide. It is shown that this region is surrounded by a different area in which the lattice is relaxed to recover the characteristic lattice parameters of LiNbO(3):Tm(3+).

Optical transition probabilities in Er3 + - and Tm3 + -doped LiLa9(SiO4)6O2 crystals

In this work, Er(3+) and Tm(3+)-doped LiLa(9)(SiO(4))(6)O(2) crystals have been grown from an Li(2)MoO(4) flux in the 1360-940 °C temperature range. Optical absorption spectra have been measured to obtain the experimental oscillator strengths of the transitions from the ground state to the excited levels. Judd-Ofelt calculations have been performed to estimate the Ω(2), Ω(4) and Ω(6) intensity parameters. The dynamics of selected Er(3+) and Tm(3+) manifolds have been investigated under selective pulsed excitation in order to determine the energy gap law by comparing the observed decay rates with the Judd-Ofelt predictions.

Energy transfer efficiency in YF3 nanocrystals: Quantifying the Yb3+ to Tm3+ infrared dynamics

In this work, we report on the determination of the infrared Yb3+ → Tm3+ energy transfer efficiency in YF3:Yb3+/Tm3+ nanocrystals through the study of Yb3+ dynamics. The obtained results are compared to those previously reported in macrocrystals to analyze possible changes related to size reduction. Luminescence lifetimes are much shorter in the nanoparticles than in bulk samples, a behavior that can be related to Yb3+ → Yb3+ migration and the enhanced surface/volume ratio of the nanoparticles. On the other hand, Yb3+ → Tm3+ energy transfer macroparameter remains unaltered, demonstrating that spectroscopic intrinsic parameters such as radiative and non-radiative probabilities are not affected by size reduction. Finally, a formula that describes Yb3+ lifetime dependence with Yb3+ and Tm3+ concentration is proposed, considering both the effects produced by migration between Yb3+ ions and energy transfer from Yb3+ to Tm3+ ions.

Control of infrared cross-relaxation in LiNbO 3 :Tm 3+ through high-pressure

The cross-relaxation process between the lower excited states of thulium ions has a strong influence on its main infrared emissions, but also in the population of higher excited states that lead to characteristic blue upconversion. This work investigates this process in LiNbO3:Tm3+ by means of time-resolved spectroscopy at high pressure. It is demonstrated that through the application of high-pressure it is possible to enhance its probability and to investigate its influence on the photoluminescence spectra and corresponding lifetimes of Tm3+. The results are analyzed in terms of the effect of high pressure on parameters such as Tm3+-Tm3+ distance through the equation-of-state of LiNbO3, refractive index or Tm3+-Tm3+ energy transfer characteristics (absorption/emission overlap integral), to conclude that the major multipole interaction responsible for cross-relaxation is the quadrupole-quadrupole interaction. This conclusion supports and clarifies previous dynamical models for energy transfer on the basis of spectroscopic studies carried out in LiNbO3:Tm3+ as a function of Tm3+ concentration.

Modelling of Laser Operation in RPE Nd3+:LiNbO3 Cannel Waveguides

In this work, laser action in RPE Nd3+:LiNbO3 is modelled by using the overlapping integrals method. Different pumping schemes, TE or TM, have been considered in order to reproduce the experimental measurements. Calculated results indicate that the slope efficiency remains basically independent on the pumping scheme while the threshold pump power increases for TE pumping