ANNUAL REPORT - MTA SzFKI

emulsions can be used in a real-time holographic interferometric set-up for the in-situ
microscopic observation of the build-up of holographic gratings in LiNbO 3 .
Hydroxyl ions in potassium lithium niobate crystals. –– The OH – stretch mode spectra
have been measured in both ferroelectric (KLN-1) and non-ferroelectric (KLN-2)
potassium lithium niobate crystals grown from different melt compositions. O-H bond
directions making angles of about 15, 60, and 15 degrees with the c-axis have been
determined for the three main OH – bands in KLN-1 peaking at about 3440, 3500, and 3520
cm -1 , respectively. Correlations have been found along the growth axis of the crystal
between the decrease of the excess Nb content, the change of the hydroxyl band
components at 3440 and 3520 cm -1 , and the Raman modes at 540 cm -1 and 640 cm -1 .
Impurity-centred oxygen tetrahedra in sillenites. –– Fundamental and multi-mode
transitions of the tetrahedral unit modes (A 1 and F 2 ) in Bi 12 SiO 20 , Bi 12 GeO 20 , and
Bi 12 TiO 20 sillenite crystals have been studied by measuring Raman scattering and FTIR
absorption spectra. The ν 1 and ν 3 frequencies related to the A 1 symmetric and F 2
asymmetric stretching modes, respectively, were obtained for MO 4 and ImO 4 tetrahedral
complexes, where M is the host matrix metal, i.e. Si 4+ , Ge 4+ , and Ti 4+ and Im is an
impurity substituting for M. The Im considered belong to three different isoelectronic
series as a) Al 3+ , Si 4+ , P 5+ , S 6+ , b) Ga 3+ , Ge 4+ , As 5+ , Se 6+ , and c) Ti 4+ , V 5+ , Cr 6+ . Ions with
different valence charges, as Cr 4+ , Cr 5+ , Cr 6+ and Mn 4+ , Mn 5+ , were also considered.
Systematic trends were put in evidence for the ν 1 and ν 3 frequency pairs as a function of M
(or Im) atomic mass and charge (Fig. 1).
1100
S 6+
1000
wavenumber (cm -1 )
900
800
700
600
P 5+
Si 4+
Al 3+
Cr 6+
Se 6+
V 5+ As 5+
Mn 5+
Cr 5+
Ge 4+
Ti 4+ Mn 4+
Cr 4+
Ga 3+
20 30 40 50 60 70 80
atomic mass
Fig. 1. Plot of ν 1 and ν 3 frequencies vs. atomic mass of impurities (Im) for different ImO 4 tetrahedral groups
in sillenites. Open symbols: ν 1 (A 1 mode); full symbols: ν 3 (F 2 mode). Circles: our work; triangles: literature.
Spectroscopy of Cu centres in lithium tetraborate single crystals. –– Cu 2+ centres in
the tissue-equivalent thermoluminescent dosimeter material, Li 2 B 4 O 7 :Cu, have been shown
by electron spin resonance experiments to substitute at the Li + site, with an appreciable
relaxation of the site and its surroundings. The singly charged Cu + centre, showing
anomalous optical emission behaviour below 6K, has been shown to occupy off-centre
positions displaced from interstitial sites on the twofold symmetry axis connecting B 4 O 7
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