Biomedical Engineering Reference
In-Depth Information
3.9
Optical transmittance spectra of 30KTP-70SiO
2
heat treated at
C for 2 h.
31
850
8
optical non-linearity. However, photo-induced second harmonic generation
(SHG) was observed from GeO
2
-doped SiO
2
glass fibers. Li et al.
31
successfully fabricated transparent bulk xKTP-(1
x)SiO
2
nanocomposites
containing nanocrystalline KTiOPO
4
(KTP) dispersed in a silica glass
matrix by the sol-gel method. They tried to identify the phase structure of
KTP/SiO
4
nanocomposites and to observe optical SHG in the transparent
nanocomposites or translucent glass-ceramics. They studied the optical
properties of the nanocomposites and found that these are transparent in
the visible range of the electromagnetic spectra. Figure 3.9 shows the optical
transmission spectrum of a 30KTP-70SiO
2
nanocomposite heat treated at
850
C. For all the samples, the UV band edge was observed near 350 nm,
which is the same as KTP crystal. This common value indicates that the UV
absorption band of glasses and nanocomposites originates from the Ti-O
band. The strong absorption near 2800 nm indicates that the materials
contain a large amount of OH
.
The SHG spectra of the glass and nanocomposite heat treated at 800
8
C
for 2 h are shown in Fig. 3.10. As multicomponent glasses do not contain
crystallites they do not exhibit SHG but the KTP/SiO
2
nanocomposite
containing KTP nanocrystals does exhibit SHG. In non-linear optical
materials, microscopic SHG structural units must be ordered spatially and
in a non-centrosymmetric manner to generate a bulk second-order effect
from the non-linear optical materials. This study clearly demonstrates that
KTP nanocrystals were formed in the KTP/SiO
2
nanocomposite and further
indicates that the SHG in the nanocomposites comes from the KTP
nanocrystals embedded in the SiO
2
glass matrix. Since the KTP nanocrystals
are randomly oriented in the SiO
2
glass matrix, it should be noted that
8
