Czochralski growth of Yb 3+ and Pr 3+ doped Ca-fluoroapatite
- PDF / 165,873 Bytes
- 4 Pages / 612 x 792 pts (letter) Page_size
- 97 Downloads / 166 Views
MATERIALS RESEARCH
Welcome
Comments
Help
Czochralski growth of Yb3+ and Pr3+ doped Ca-fluoroapatite A. Caprez, P. Mikhail, C. Schwecke, and J. Hulliger Department of Chemistry and Biochemistry, University of Berne, CH-3012 Berne, Switzerland (Received 19 March 1997; accepted 12 August 1997)
Pure, Pr3+ , and Yb3+ doped Ca-fluoroapatite (Ca-FAP) crystals were grown by the Czochralski method. The effective distribution coefficient keff for Yb3+ was 0.5. For Pr3+ a very high keff of 1.4 was obtained. Values for keff are discussed in terms of an elastic model accounting for the strain energy originating from the difference in the size of Ln3+ ions. The Ln3+ concentrations were measured by absorbance spectroscopy, by inductively coupled plasma optical emission spectroscopy, and by electron microprobe analyses.
The apatite structural family [A10 (MO4 )6 X2 ], represented by a large class of natural and synthetic compounds, crystallizes in a few different, but related, hexagonal and pseudohexagonal structures.1,2 Ca5 (PO4 )3 F (Ca-FAP), apatite, belongs to the hexagonal space group P63ym with Z 2.3 The ten Ca2+ ions are distributed over two crystallographically different sites: 4 Ca2+ are at site I with site symmetry 3 and 9-fold coordination by O2– ; 6 Ca2+ are at site II with 6fold O2– and one F– coordination.4 Lanthanide dopants predominantly enter the Ca(II) site which provides a low energy charge compensation mechanism5 : The Ln3+ ion substitutes for Ca2+ (II), whose nearest neighbor F– ion is replaced by an O2– .6 Because only one F– ion is available for bonding to every three Ca(II) ions, at most only two Ln3+ ions for every ten Ca2+ in the unit cell can enter the structure without creating an additional charge compensation mechanism.5 In this study we found that co-doping with, e.g., Na+ had no influence on the effective distribution coefficient keff of Yb3+ . Yb3+ doped Ca-FAP and Sr-FAP are currently of interest because of efficient solid state laser properties when pumped by InGaAs diode sources.7–9 Recently, a diode-pumped, Q-switched Sr–FAP : Yb3+ laser (1047 nm) has been demonstrated.9 In this work we have explored Ca-FAP crystal growth for two reasons: (i) determination of the effective distribution coefficients keff of Yb3+ and Pr3+ , and (ii) the potential of the Ca-FAP host-lattice as a new material for Pr3+ hyperfine pumped optical hole burning (H-OHB). An important parameter for the application of OHB in optical memories is the homogeneous linewidth of the holes, which is influenced by flip-flop processes of the nuclear magnetic moments of the host material.10 In a previous study we have discussed possible low nuclear spin density host materials for Pr3+ of Eu3+ H-OHB.10 However, a major drawback of selected compounds is that they showed only low doping levels and some effects of disorder in the nearest neighborhood of Ln3+ due to a heterovalent mechanism of substitution. Al3210
http://journals.cambridge.org
J. Mater. Res., Vol. 12, No. 12, Dec 1997
Downloaded: 18 Mar 2015
though Ca-FAP will
Data Loading...
