-
[show abstract]
[hide abstract]
ABSTRACT: The potential use of CdTe quantum dots as luminescence nano-probes for lifetime fluorescence nano-thermometry is demonstrated. The maximum thermal sensitivity achievable is strongly dependent on the quantum dot size. For the smallest sizes (close to 1 nm) the lifetime thermal sensitivity overcomes those of conventional nano-probes used in fluorescence lifetime thermometry.
Small 06/2012; 8(17):2652-8. · 8.35 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A new approach to deep tissue imaging is presented based on 8 nm CdTe semiconductor quantum dots (QDs). The characteristic 800 nm emission was found to be efficiently excited via two-photon absorption of 900 nm photons. The fact that both excitation and emission wavelengths lie within the "biological window" allows for high resolution fluorescence imaging at depths close to 2 mm. These penetration depths have been used to obtain the first deep tissue multiphoton excited fluorescence image based on CdTe-QDs. Due to the large thermal sensitivity of CdTe-QDs, one may envisage, in the near future, their use in high resolution deep-tissue thermal imaging.
Nanoscale 11/2011; 4(1):298-302. · 5.91 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Infrared to visible second harmonic generation (SHG) has been demonstrated from 40 nm Sr0.6Ba0.4Nb2O6 nanoparticles in a broad spectral range of infrared fundamental wave excitation (800–1200 nm). The efficiency for SHG is compared with that obtained from powdered samples of larger crystallite sizes so that the mechanism leading to optical frequency conversion is discussed. The obtained results point out the possibility of using nonlinear nanoparticles for multifrequency optical imaging.
Journal of Physics D Applied Physics 04/2009; 42(10):102003. · 2.54 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The LiNbO(3) congruent crystals doped with small Nd concentrations, <1 mol% Nd, and co-doped with Mg ions, 0-9 mol% Mg, were systematically investigated by means of micro-Raman spectroscopy in the Y and Z crystal directions. Results obtained from an undoped congruent crystal, an Nd-doped crystal, a Mg-doped crystal and Nd, Mg-co-doped crystals are compared. From the analyses of the results obtained in the Y direction, the Nd and Mg content dependence of the two lowest-Raman A(1)(TO(1)) and A(1)(TO(2)) modes, the half-width composition and the area ratio of the A(1)(TO(4)) and E(TO(8)) bands, we reached several conclusions about the incorporation mechanism of the Nd and Mg ions into the LiNbO(3) lattice. Likewise the Raman shift and half-width of the E(TO(1)) and E(TO(7)) modes were investigated in the Z direction. Results indicate that Mg and Nd ions are located in the Li site for low doping concentrations and for larger concentrations there is a replacement in both Li and Nb ion sites.
Journal of Physics Condensed Matter 04/2009; 21(14):145401. · 2.55 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The LiNbO3 congruent crystals doped with small Nd concentrations, <1 mol% Nd, and co-doped with Mg ions, 0–9 mol% Mg, were systematically investigated by means of micro-Raman spectroscopy in the Y and Z crystal directions. Results obtained from an undoped congruent crystal, an Nd-doped crystal, a Mg-doped crystal and Nd, Mg-co-doped crystals are compared. From the analyses of the results obtained in the Y direction, the Nd and Mg content dependence of the two lowest-Raman A1(TO1) and A1(TO2) modes, the half-width composition and the area ratio of the A1(TO4) and E(TO8) bands, we reached several conclusions about the incorporation mechanism of the Nd and Mg ions into the LiNbO3 lattice. Likewise the Raman shift and half-width of the E(TO1) and E(TO7) modes were investigated in the Z direction. Results indicate that Mg and Nd ions are located in the Li site for low doping concentrations and for larger concentrations there is a replacement in both Li and Nb ion sites.
Journal of Physics Condensed Matter 03/2009; 21(14):145401. · 2.55 Impact Factor
-
The Journal of chemical physics 01/2009; 129(24):249901. · 3.09 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The temperature and compositional dependences of thermo-optical properties of neodymium doped yttrium aluminum garnet (YAG) crystals and fine grain ceramics have been systematically investigated by means of time-resolved thermal lens spectrometry. We have found that Nd:YAG ceramics show a reduced thermal diffusivity compared to Nd:YAG single crystals in the complete temperature range investigated (80-300 K). The analysis of the time-resolved luminescent properties of Nd(3+) has revealed that the reduction in the phonon mean free path taking place in Nd:YAG ceramics cannot be associated with an increment in the density of lattice defects, indicating that phonon scattering at grain boundaries is the origin of the observed reduction in the thermal diffusivity of Nd:YAG ceramics. Finally, our results showed the ability of the time-resolved thermal lens to determine and optimize the thermo-optical properties of Nd:YAG ceramic based lasers.
The Journal of chemical physics 10/2008; 129(10):104705. · 3.09 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Different values of the electronic charge provided by a direct electron beam writing system have been used to produce polarization inverted domain regions in the micrometer range on Nd3+ optically activated LiNbO3. The effect of the electronic charge on the Nd3+ center structure has been studied by means of low-temperature luminescence from Nd3+ ions. The axial crystal field acting on the Nd3+ centers has been analyzed through the 4F3/2 energy-level splitting of the Nd3+ ions. From there we have determined the position of Nd3+ ions into the Li+ octahedra for the different unequivalent centers in domains reversed with different electronic doses. The results show that the axial crystal field acting on the unequivalent Nd3+ centers can be selectively modified by means of the different doses applied to produce the inversion of the polarization. Moreover, a control of the discrete shifts suffered by the Nd3+ ions into the Li+ octahedra after the inversion process can be carried out in the range 0–0.02 Å by selecting the type of Nd center to be shifted by means of the different electronic charge. The behavior of each Nd3+ center after the polarization inversion under different doses can be discriminated and the different nature, as well as the polar character of the Nd3+ centers, is clearly manifested.
Phys. Rev. B. 07/2008; 78(1).
-
[show abstract]
[hide abstract]
ABSTRACT: We report on continuous wave laser oscillation of trivalent ytterbium ions in the frequency converter Yb3+:Sr0.6Ba0.4Nb2O6 ferroelectric laser crystal. Pump induced thermal loading has been used to drive the crystal from its ferroelectric to paraelectric phase. Stable laser radiation at 1070 nm was found in both phases while a bistable laser output is observed through phase transition. In addition, diffuse green (535 nm) radiation was generated by self-frequency doubling of the fundamental laser radiation because of the random distribution of microferroelectric domains existing in the ferroelectric as grown crystal.
Applied Physics Letters 05/2008; 92(18):181107-181107-3. · 3.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We report on a simple and accurate method for determination of thermo-optical and spectroscopic parameters (thermal diffusivity, temperature coefficient of the optical path length change, pump and fluorescence quantum efficiencies, thermal loading, thermal lens focal length, etc) of relevance in the thermal lensing of end-pumped neodymium lasers operating at 1.06- and 1.3- microm channels. The comparison between thermal lensing observed in presence and absence of laser oscillation has been used to elucidate and evaluate the contribution of quantum efficiency and excited sate absorption processes to the thermal loading of Nd:YAG lasers.
Optics Express 05/2008; 16(9):6317-23. · 3.59 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The laser performance of poled and unpoled neodymium-doped strontium barium niobate crystals has been compared. We have found that the random distribution of microferroelectric domains, characteristic of as-grown crystals, leads to a relevant improvement in the laser performance. From the analysis of the optical distortion effects induced by both poled and unpoled crystals we have concluded that the compensation effects taking place between adjacent microdomains inside the active volume are at the origin of this improvement.
Journal of Applied Physics. 09/2007; 102(5):053101-053101-4.
-
[show abstract]
[hide abstract]
ABSTRACT: The luminescence of Nd(3+) ions in Nd(x)Y(1-x)Al(3)(BO(3))(4) (Nd:YAB) single crystals has been investigated as a function of the neodymium concentration in order to evidence the relation between the structural and spectroscopic properties in this nonlinear laser system. The analysis of the experimental data allowed us to individuate four different composition ranges. For moderate concentrations (x<0.2) the lattice parameters are nearly constant, and the emission spectra arise from Nd(3+) ions in unperturbed crystal sites. For concentrations in the 0.2<x<0.75 range the lattice parameters notably depend on the neodymium content, and a concomitant variation of the luminescence features is observed. In the 0.75<x<0.9 range a hexagonal to monoclinic phase transition takes place: the structural disorder is evidenced well by the broadening of the emission lines and by discontinuities in the concentration behaviour of other indicators such as the crystal-field strength, energy transfer parameters, etc. Finally, for x>0.9 the final formation of the NdAl(3)(BO(3))(4) (NAB) monoclinic phase is complete, and a new local ordering around Nd(3+) is very evident in the spectral features.
Journal of Physics Condensed Matter 06/2007; 19(24):246204. · 2.55 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The luminescence of Nd3+ ions in NdxY1−xAl3(BO3)4 (Nd:YAB) single crystals has been investigated as a function of the neodymium concentration in order to evidence the relation between the structural and spectroscopic properties in this nonlinear laser system. The analysis of the experimental data allowed us to individuate four different composition ranges. For moderate concentrations (x<0.2) the lattice parameters are nearly constant, and the emission spectra arise from Nd3+ ions in unperturbed crystal sites. For concentrations in the 0.2<x<0.75 range the lattice parameters notably depend on the neodymium content, and a concomitant variation of the luminescence features is observed. In the 0.75<x<0.9 range a hexagonal to monoclinic phase transition takes place: the structural disorder is evidenced well by the broadening of the emission lines and by discontinuities in the concentration behaviour of other indicators such as the crystal-field strength, energy transfer parameters, etc. Finally, for x>0.9 the final formation of the NdAl3(BO3)4 (NAB) monoclinic phase is complete, and a new local ordering around Nd3+ is very evident in the spectral features.
Journal of Physics Condensed Matter 05/2007; 19(24):246204. · 2.55 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In this work the origin of the phase transition induced gain depression in diode pumped Nd3+ doped Sr0.6Ba0.4(NbO3)2 lasers has been systematically investigated. The mechanisms capable of intracavity beam distortions are discussed and their relative contribution to the gain depression is investigated. We also provide evidence of two effects: a phase transition induced polarization switching and an enhancement in the laser performance when phase transition is overcome.
Journal of Applied Physics 12/2006; 100(11):113114-113114-8. · 2.17 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In this paper the temperature evolution of the main Raman peak at about 630 cm−1 has been studied in order to detect the ferroelectric to paraelectric phase transition in strontium barium niobate (SrxBa1−xNb2O6) crystals with different stoichiometries (x = 0.33, 0.5 and 0.61). Both its peak wavenumber and width have been shown to be strongly dependent on temperature and display clear anomalies around the Curie temperature. The obtained results manifest the usefulness of simple unpolarized Raman spectra to probe the changes in Tc as a result of modifications in the crystal composition.
Journal of Physics D Applied Physics 11/2006; 39(23):4930. · 2.54 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We report on the polarization and temperature dependence of optical distortions of beams passing through a Nd3+-doped Sr0.61Ba0.39Nb2O6 laser crystal. For temperatures close to TC ( ≈ 70 ºC), a strong enhancement in the optical distortion of a nonabsorbed beam takes place, related to the temperature dependence of the r33 electro-optical coefficient during phase transition. From pump and probe experiments, we have concluded that the traditional 808 nm Nd3+ pumping radiation also causes optical distortions, especially for extraordinary polarized radiation.
Applied Physics Letters 04/2006; 88(16):161116-161116-3. · 3.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In this Letter we have used the optical pump induced thermal loading to drive Nd(3+) a doped Sr(0,47)Ba(0.53)(Nb)(3))(2) laser crystal during laser operation through its ferroelectric phase transition. We demonstrate that lasing is possible below, at, and above phase transition. For temperatures close to (approximately 105 degrees C) the spatial distribution of laser radiation is remarkably affected. This feature, which leads to a laser gain depression, can be explained in terms of the strong temperature dependence of the thermo-optic coefficient during phase transition. Additionally, the visible radiation generated by intracavity self-frequency doubling disappears when the phase transition is undergone, showing a bistable behavior. The results provide fundamental information on physical parameters along the phase transition and will stimulate further work in the fields of nonlinear optics, optical switching, and data storage.
Physical Review Letters 01/2006; 95(26):267401. · 7.37 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The main properties of the Nd3+→Yb3+ (4F3/2,2F7/2⃗4I9/2,2F5/2) energy transfer in yttrium aluminum borate nonlinear laser crystal have been studied. This host has been found especially suitable for efficient Nd3+→Yb3+ energy transfer because of the good matching between phonon energy and the 4F3/2(Nd3+)-2F7/2(Yb3+) energy gap (≅1000 cm-1). Energy-transfer probabilities in excess of 65% have been obtained for a Nd3+ (10 at. %) and Yb3+ (5 at. %) codoped sample. The influence of both crystal temperature and Nd3+ concentration on the transfer probability has been investigated. In the 15–350 K range the Nd3+→Yb3+ energy-transfer efficiency increases with temperature, whereas for crystal temperatures above 350 K the Nd3+←Yb3+ back transfer is activated, leading to a decrease in the effective Nd3+→Yb3+ energy-transfer probability. The analysis of the decay curves obtained after pulsed excitation has been used to determine the multipole character of the Nd3+-Yb3+ interaction. The donor-acceptor energy-transfer microparameter was determined [CDA(Nd3+→Yb3+)≅18×10-39cm6/s], and compared to those obtained for other Nd3+-Yb3+ co-doped materials.
Phys. Rev. B. 07/2003; 68(3).
-
[show abstract]
[hide abstract]
ABSTRACT: An all-solid-state simultaneous green and red laser source is demonstrated based on a diode-pumped Nd3+-doped crystal operating in the 4F3/2→4I13/2 laser channel. Coherent green radiation was achieved by sum frequency mixing of pump (800 nm) and fundamental (1.3 μm) radiation inside an intracavity KTP crystal. At the same time, laser radiation in the red was obtained by second harmonic generation of infrared (IR) radiation in an additional intracavity KTP crystal. We have tested this scheme by using both YAG and YVO host crystals for the Nd3+ ions. The influence of IR multiline oscillation on the spectral and spatial characteristics of visible radiation is discussed.
Journal of Physics D Applied Physics 10/2002; 35(21):2711. · 2.54 Impact Factor
-
Ferroelectrics. 01/2002; 273(1):193-198.
