No abstract

In the present study, various concentrations of ErF 3 -doped CaF 2 crystals were grown using the vertical Bridgman method. The Judd-Ofelt intensity parameters t (t = 2, 4, 6) for f-f transitions of Er 3+ ions were determined from optical absorption spectra. The concentration dependence of the intensity parameters radiative transition probability, oscillator strength, branching ratio and radiative lifetime was also investigated. The predicted radiative lifetimes were compared with those of the Er 3+ transitions reported in various hosts. Apart from the green and red emissions, reported by other researchers, a UV (314 nm) emission band was observed, not reported previously.

Calcium fluoride crystals doped with YbF3 and co-doped with LiF and NaF were grown using the vertical Bridgman method. Several of rare-earth ions (such as Eu, Sm, Ho, Tm, and Yb) can be stabilized in the divalent state in the CaF2. The change of valence was attained by various methods. The optical absorption spectra reveal the characteristic absorption bands of the Yb 3+ and Yb 2+ ions. This means that the developed crystal growth process achieves a good Yb 3+ to Yb 2+ conversion in the as-grown crystals. The influence of other impurities, such as Na + or Li + , on the absorption and emission spectrum of YbF 3 -doped CaF 2 was studied. The Li + and Na + ions drastically decrease the absorption coefficient of the Yb 2+ ions in the UV band and the emission intensity by excitation in 230 nm.

Calcium fluoride crystals doped with YbF3 and codoped with NaF, LiF were grown using the vertical Bridgman method. The effect of Na+ and Li+ ions on the optical and dielectric spectra was studied. The relaxation parameters (the activation energy for dipole reorientation and relaxation time constant) and the number of the dipoles, ND, that contribute to the dielectric relaxation have been determined from the dielectric spectra. The correlation between ND and the optical spectra is also discussed. A comparison of our results with those obtained by other authors is also given. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

No abstract