35 research outputs found
Optical properties of active ions around the ferro-paraelectric phase transition in SBN crystals
No full textNew results on the evolution of the emission of Nd3+ doped SrxBa1-xNb2O5 crystal during the ferroelectric phase transition are presented and compared to those previously obtained for Cr3+ and Yb3+ doped SrxBa1-xNb2O5. We have observed that Nd3+ emission is insensitive to the structural changes suffered by the crystal during the phase transition, contrary to the observations obtained for the cases of the Cr3+ and Yb3+ doped crystals. The results are interpreted in terms of the different lattice sites occupied by the optically active ions in the SrxBa1-xNb2O5 crystal
Spectroscopic study of Yb3+ centres in the YAl3(BO3)4 nonlinear laser crystal
No full textA spectroscopic study of Yb3+ ions in YAl3(BO3)(4) laser crystals is presented. Polarized absorption and site selective spectroscopy experiments at low temperature have been used to determine the presence of two different Yb3+ centres in this host crystal in the concentration range 0.2-9 at.%. The contribution of these centres to the absorption spectra has been found to be dependent on the total Yb3+ concentration, and the Stark energy level diagrams corresponding to the different Yb3+ centres have been determined. The importance of electron-phonon coupling, in the optical transitions of Yb3+ ions has been also pointed out
Influence of Nd3+ and Yb3+ concentration on the Nd3+ --> Yb3+ energy-transfer efficiency in the YAl3(BO3)4 nonlinear crystal: determination of optimum concentrations for laser applications
No full textThe Nd3+ --> Yb3+ energy-transfer efficiency in the YAl3(BO3)(4) nonlinear laser crystal has been investigated as a function of both donor (Nd3+) and acceptor (Yb3+) concentrations. An analytical expression giving the value of the energy-transfer rate for any Nd3+ and Yb3+ concentrations has been obtained on the basis of the analysis of experimental data. From this expression, a basic model is proposed to determine the Nd3+ and Yb3+ concentrations that optimize the Yb3+ output laser power obtained from a 808-nm diode-pumped Nd3+; Yb3+: YAl3(BO3)(4) crystal
Phase transition in SrxBa1-xNb2O6 ferroelectric crystals probed by raman spectroscopy
No full textIn 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 T-c as a result of modifications in the crystal composition
Temperature dependence of Nd3+-Yb3+ energy transfer in the YAl3(BO3)4 nonlinear laser crystal
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Temperature dependence of Nd3+->Yb3+ energy transfer in the YAl3(BO3)4 nonlinear laser crystal
No full textThe temperature dependence of the Nd3+-> Yb3+ energy-transfer rate in the YAl3(BO3)(4) nonlinear laser crystal has been investigated from the analysis of fluorescence decay curves recorded in the 10-600 K range. Three different regimes, independent on the dopant concentration, have been observed in the thermal behavior of the Nd3+-> Yb3+ energy-transfer rate. By comparing experimental results with theoretical predictions based on the Dexter model [J. Chem. Phys. 21, 836 (1953)], the origin of these different regimes has been explained. In addition, the influence of temperature and of both Nd3+ and Yb3+ concentrations on the Nd3+<- Yb3+ energy back-transfer rate has been also investigated, concluding that it is a migration-assisted energy-transfer process. Finally, the populations of both Nd3+ and Yb3+ metastable states achieved after continuous-wave Nd3+ excitation have been calculated and measured and results have been explained in terms of the thermal behavior of both forward- and back-transfer rates
Nd3+ --> Yb3+ energy transfer in the YAl3(BO3)4 nonlinear laser crystal
No full textThe main properties of the Nd3+→Yb3+ ( 4F3/2, 2F7/2→4I 9/2, 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(Yb 3+) 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+→Yb 3+ 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 Nd 3+ →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+)≅ 18×10-39 cm 6/s], and compared to those obtained for other Nd 3+-Yb3+ co-doped materials
Lanthanide doped strontium barium niobate: Optical spectroscopy and local structure at the impurity sites
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