Nucleation efficiency of erbium and ytterbium fluorides in transparent oxyfluoride glass-ceramics
- PDF / 662,204 Bytes
- 10 Pages / 612 x 792 pts (letter) Page_size
- 89 Downloads / 195 Views
. Patriarche Laboratoire de Photonique et Nanostructures, CNRS-UPR20, 91460 Marcoussis, France (Received 12 July 2004; accepted 10 November 2004)
Oxyfluoride glasses (GeO2–PbO–PbF2) doped with erbium and/or ytterbium fluorides were prepared. Highly transparent glass-ceramics, containing –PbF2 nanocrystallites, were successfully obtained by controlled glass devitrification and were studied as they could lead to promising optical applications. To characterize the samples, differential thermal analysis, x-ray diffraction, and transmission electron microscopy were performed, revealing a variation of the crystallites size, the crystallites number and –PbF2 crystallization temperature according to the doping ion. Indeed, the analyses indicated differences between erbium and ytterbium fluorides in promoting the crystallization of the fluoride phase. Although both fluorides act as seeds for –PbF2 heterogeneous nucleation, erbium fluoride has higher nucleation efficiency than ytterbium fluoride and runs the nucleation process in co-doped samples. Energy dispersive x-ray microanalysis insured high rare-earth segregation into the crystallites, proving the formation of a solid solution Pb1−x−yErxYbyF2 + x+y, also confirmed by the unit cell parameter study.
I. INTRODUCTION
Recently, transparent rare-earth doped glass-ceramics have aroused interest from the viewpoint of lasers applications.1–3 Indeed, beside their high mechanical, electrical, and thermal characteristics, doped glass-ceramics possess interesting optical properties comparable to those of doped crystals. Glass-ceramics are composed of a glassy matrix and a crystalline phase usually obtained by a controlled heat treatment of a starting glass. The transparency can be reached if the dispersed crystalline phase size is small compared to the transmitted light wavelengths or if the optical isotropy (i.e., identical refractive indices) is achieved despite the phase variation. It has been shown that the rare-earth ions are mainly concentrated into the crystalline phase as they initiate the heterogeneous nucleation.4,5 Through this segregation, optical properties of the doped glass-ceramics appear closer to those of doped crystals than to those of doped glasses. Indeed, the inhomogeneous linewidth of the absorption and emission spectra is reduced after the glasses devitrification treatment.6 a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0051 472
J. Mater. Res., Vol. 20, No. 2, Feb 2005
Among the studied transparent glass-ceramics, the oxyfluoride systems are of great interest because the fluoride environment of the lanthanide ions improves several optical properties. Indeed, as the phonon cut-off frequency is usually twice lower in a fluoride environment than in an oxide one, the nonradiative transitions are reduced in an oxyfluoride glass-ceramic, inducing an increase of the rare-earth excited-state lifetime.7 The following glass-ceramic compositions were developed: either PbF2 in PbO–GeO2 matrix5 or in S
Data Loading...
