Spectroscopic Properties of alkaline earth bismuth borate glasses doped with TiO 2 4.1 Introduction: Among various transition metal ions, doping of TiO 2 to alkaline earth bismuth borate glass augments the applications of base glass due to the similar advantages of TiO 2 , such as high transparency in the visible to near-infrared wavelength region, high refractive index [1] with bismuth borate glasses. Generally, in the glass matrix titanium ions exists in Ti 4+ state with TiO 4 , TiO 6 and sometimes with TiO 5 (comprising of trigonal bipyramids) structural units. Murali Krishna et al [2] observed that during melting process some of Ti 4+ ions might be reduced into Ti 3+ valence state in certain glass matrices and acts as modifiers. As a consequence of such variation in coordination and valence of titanium ions in the glass network produces structural modification and local-field variation in the structure which influences its potential applications. The presence of Ti 4+ ions makes glass to be suitable for non-linear optical devices, since the empty or unfilled d-shells of these ions contribute more strongly to nonlinear polarizabilities. Usually, the d-orbital contribution to non-linear polarizability is found to be more for bond lengths less than 2 Å; the bond length of Ti-O is estimated to be 1.96 Å. Literature survey on the glasses containing TiO 2 indicates that these glasses possess negative non-linear refractive index that induces self-focusing radiation beam in the material; as a result, the devices can be operated at a smaller input power. Nevertheless, the investigation on the co-ordinate chemistry of Ti 4+ and Ti 3+ ions in Bi 2 O 3 –B 2 O 3 glass network is of interest itself because, these ions are expected to
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Spectroscopic Properties of alkaline earth bismuth borate glasses doped
with TiO2
4.1 Introduction:
Among various transition metal ions, doping of TiO2 to alkaline earth bismuth
borate glass augments the applications of base glass due to the similar advantages of
TiO2, such as high transparency in the visible to near-infrared wavelength region, high
refractive index [1] with bismuth borate glasses. Generally, in the glass matrix titanium
ions exists in Ti4+ state with TiO4, TiO6 and sometimes with TiO5 (comprising of
trigonal bipyramids) structural units. Murali Krishna et al [2] observed that during
melting process some of Ti4+ ions might be reduced into Ti3+ valence state in certain
glass matrices and acts as modifiers. As a consequence of such variation in
coordination and valence of titanium ions in the glass network produces structural
modification and local-field variation in the structure which influences its potential
applications.
The presence of Ti4+ ions makes glass to be suitable for non-linear optical
devices, since the empty or unfilled d-shells of these ions contribute more strongly to
nonlinear polarizabilities. Usually, the d-orbital contribution to non-linear polarizability
is found to be more for bond lengths less than 2 Å; the bond length of Ti-O is estimated
to be 1.96 Å. Literature survey on the glasses containing TiO2 indicates that these
glasses possess negative non-linear refractive index that induces self-focusing radiation
beam in the material; as a result, the devices can be operated at a smaller input power.
Nevertheless, the investigation on the co-ordinate chemistry of Ti4+ and Ti3+ ions in
Bi2O3–B2O3 glass network is of interest itself because, these ions are expected to
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influence the structural properties of the glasses to a large extent. By keeping the
potential applications of titanium ions doped glasses in view, in the preset chapter six
samples of composition 10MO.20Bi2O3.(70-x)B2O3.xTiO2, [R=Ca, Sr] with x=0, 0.5,
1.0 (Wt%) were prepared and their specific spectroscopic properties we studied. Fig.
4.1 represents the physical appearance of 2 mm thick samples. The details of
composition are as follows:
CT0: 10CaO-20Bi2O3-70.0B2O3
CT05: 10CaO-20Bi2O3-69.5B2O3-0.5TiO2
CT10: 10CaO-20Bi2O3-69.0B2O3-1.0TiO2
ST0: 10SrO-20Bi2O3-70.0B2O3
ST05: 10SrO-20Bi2O3-69.5B2O3-0.5TiO2
ST10: 10SrO-20Bi2O3-69.0B2O3-1.0TiO2
Fig. 4.1 Physical appearance of 2.0 mm thick TiO2 doped glass samples.
4.2 Brief review on the literature of TiO2 doped materials:
Srinivasa Rao et al [3] studied the dielectric and spectroscopic properties of
TiO2 mixed lithium aluminium zirconium silicate glasses and observed that with
increase in titanium content in the glass matrix visible luminescence efficiency is
increased and octahedral Ti4+ ions are responsible for such luminescence emission.
Besides, dielectric parameters are observed to decrease with increase in TiO2 due to
increased proportion of Ti4+ ions in network forming positions rather than interstitial
CT0 CT05
CT10
ST05 ST10
ST0
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spaces and some of Ti4+ ions are found to reduce to Ti3+ ions in the glass matrix.
Lebedev et al [4] produced TiO2 doped silica host glasses with laser torch technique
and investigated the luminescence, Raman and ESR spectroscopy. They observed a
luminescence due to oxygen deficient centers produced as a result of chemical reaction
between titanium and silica by forming Si-O-Ti bonds. In addition the luminescence
intensity decreased with increase in titanium content. Ting [5] et al prepared Er3+-Yb3+
codoped TiO2 films on fused silica by sol-gel process. They studied physical
characteristics and infrared fluorescence properties at lower annealing temperature than
SiO2 films with Er3+-Yb3+ codoped, annealed at optimal temperature of 985oC. The
microstructure and optical properties of MgO-TiO2 composite thinfilms prepared by
radio frequency magnetron sputtering were studied by Ye et al [6] and they observed a
broad photo luminescence band in the visible region with high Mg content and was
considered resulted from oxygen vacancies. Nagaraju et al [7] investigated the
spectroscopic properties like optical absorption, IR, ESR, luminescence and magnetic
susceptibility on PbO-As2O3 glasses crystallized with TiO2 and confirmed the presence
of Pb3O4, Ti[As2O7], Pb[As2O6], Pb3[AsO4]2, PbTi3O7 and Ti2O3 crystal phases in the
glass matrix. Abdel-Baki et al [8] optically characterized the xTiO2-(60-x)SiO2-40Na2O
glasses, especially absorption edge, Fermi level, electronic polarizability and optical
basicity. Raghavaiah et al [9] studied the spectroscopic properties of titanium ions of
various concentrations in PbO-Sb2O3-As2O3 glasses and concluded that glasses with
0.25 mol% of TiO2 are more suitable for the practical applications like non-linear
optical devices. Song et al [10] demonstrated the conversion of near-ultraviolet
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radiation of 250-350 nm into visible emission of 450-600 nm and NIR emission of 970-
1100 nm in the Yb2O3 doped transparent 40SrO-20TiO2-40SiO2 glasses. X ray
absorption near edge structure analysis of valence state and coordination geometry of
Ti ions in borosilicate glasses were done by Yang et al [11]. From their study they
concluded that conclusion that usage of reducing agent during melting process favors
the formation of fourfold coordinated Ti4+ ions in sodium borosilicate glasses.
4. 3 Results and Discussion:
4. 3. 1 Characterization and Physical parameters:
Figure 1 shows the XRD patterns of 0.5 wt% TiO2 doped (CT5 and ST5) glass
samples. The absence of sharp Bragg peaks in the XRD patterns confirmed the
amorphous nature and the observed broad humps are due to the short range periodicity
Fig 4.2. XRD patterns of CT05 and ST05 glass samples
20 30 40 50 60 70 80
CT05
ST05
Inte
nsity
(ar
b. u
nits
)
2θ
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in the prepared samples. Remaining samples also showed the similar behavior. The
measured density value of CT0 glass sample is 4.3006 g/cm3 and it is increased with the
integration of SrO. This is expected due to replacement of a lighter cation by heavier
one since the density of a glass is very sensitive to the ionic size and atomic weight. In
CaO mixed glasses the density is increased with doping of TiO2 as given in Table 4.1.
The increase in density with TiO2 doping in CaO mixed glasses is also explained in the
similar manner as lighter B3+ is replaced by heavier Ti4+ ions.
Table 4.1 The density (�), molar volume (Vm), refractive index (�), Ti4+
ion
concentration (Ni), average boron-boron separation B Bd − and theoretical optical
basicity (�th) of the glasses 10MO.20Bi2O3.(70-x)B2O3.xTiO2 [R=Ca, Sr].