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2017
ACL
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K.V.Krishnaiah, Y.Ledemi C.Genevois, E.Véron, X.Sauvage, S.Morency, E.Soares de Lima Filho, G.Nemova, M.Allix, Y.Messaddeq R.Kashyap, 'Ytterbium-doped oxyfluoride nano-glassceramic fibers for laser cooling', Opt. Mat. Express 7 1980-1994 (2017) doi:10.1364/ome.7.001980
Ytterbium (Yb3+)-doped oxyfluoride SiO2-Al2O3-CdF2-PbF2-YF3 glass and nano-glass-ceramic (i.e. glass-ceramics containing nanocrystals) single-index optical fibers were fabricated using two methods: by traditional glass preform drawing and by the crucible technique (‘direct-melt process’). The latter technique permitted the fabrication of perfectly
vitreous optical fibers (of about 200 μm diameter), leading subsequently to the fabrication of nano glass-ceramic fibers by a well-controlled heat-treatment process above the glass transition temperature. Structural characterizations have (i) confirmed the vitreous state (absence of crystals) of the glass preforms and
the glass fiber obtained from the ‘direct-melt
process’ and, (ii) evidenced the formation of Pb
1-x-y-zCdxYyYbzF2 (x + y + z ≈0.3-0.4) fluorite
nanocrystals in the final glass-ceramic fibers.
In particular, the nanocrystal size was found to
be rather homogenous and smaller than 10 nm from TEM measurements for the nano-glass-ceramic fibers produced by controlled crystallization. The absolute photoluminescence quantum efficiency, mean fluorescence wavelength and anti-Stokes fluorescence of the Yb
3+-doped fibers were measured upon laser excitation at wavelengths of 940 nm, 975 nm and
1030 nm, respectively. As expected, higher photoluminescence quantum yield in the near
infrared (0.95, close to unity) was obtained fo
r the nano-glass-ceramic fiber when compared
with the glass-fiber. Theoretical calculations
were also carried out, showing that optical
refrigeration would be achievable from thes
e chemically stable and durable nano-glass-
ceramic fibers provided that 95% (segregation ratio) of Yb3+ ions are incorporated into the
fluorite nanocrystals.
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