Chemistry Reference
In-Depth Information
2 %ErF
3
, leading to a crystallite composition of Pb
0.82
Er
0.18
F
2.18
[12]. The single-crystal,
with the Pb
0.8
Er
0.2
F
2.2
composition, was grown by the Bridgman method [12].
The absorption line shape of Er
3
þ
in the glass-ceramic and in the single-crystal is very
similar, suggesting that, in both materials, Er
3
þ
ions occupy similar sites.
The absorption line of Er
3
þ
in the glass-ceramic is slightly broader than that of Er
3
þ
in
the single-crystal, which could be explained by the fact that, in glass-ceramics, Er
3
þ
ions
are in nanosized particles and can be perturbed by the neighbouring glassy matrix.
The absorption cross-section was found to be higher in the glass ceramic than in the
single-crystal. In the nanosized crystallites, some Ln
3
þ
ions are close to the interface with
the oxide matrix and are likely to have high oscillator strength [64].
2,0
glass-ceramic
1,5
1,0
0,5
0,0
single-crystal
536
538
540
542
544
546
λ
(nm)
Figure 9.23 Absorption cross-section of the
4
I
15/2
!
4
S
3/2
transition of Er
3þ
in a 50GeO
2
:
40PbO:10PbF
2
glass ceramic and a
b
-PbF
2
single-crystal
9.6.3.2 Fluorescence Decays
A comparison was established between the lifetimes of Er
3
þ
in the glass ceramic and in the
Pb
0.8
Er
0.2
F
2.2
bulk single-crystal [12]. In the glass ceramic, the
4
I
13/2
fluorescence lifetime
of Er
3
þ
is measured as 2.1 - 0.1 ]ms, whereas it is 2.5 - 0.1 ms in the single-crystal.
The shorter lifetime in the glass ceramic is probably due to the effect of the oxide matrix
incorporating the nanoparticles. Indeed, several studies have proved that the oxide glassy
matrix interacted with the rare-earth ions situated inside the nanosized crystallites and
influenced their spectroscopic properties [65, 66]. Indeed, those Er
3
þ
ions close to the
nanocrystallite/glass interface are in distorted sites. As the distortions lower the symmetry,
this could result in an increase in the electric dipole transition probability and consequently
decrease the radiative lifetime. Moreover, those Er
3
þ
ions close to the surface of the
crystallites can be sensitive to the presence of oxide ions in their coordination polyhedron,
inducing multiphonon nonradiative contribution to the Er
3
þ
de-excitation and lowering the
lifetime.
