Geoscience Reference
In-Depth Information
200
200
150
150
100
(a)
50
(b)
100
0
300
400 500 600 700 800
50
(a)
(b)
0
0
500
1000
1500 2000
Wavelength (nm)
2500
3000
3500
Figure 7.28 Absorption spectra of various BSO samples
[134]
.
Exposing them at 10 K to 3.3
3.45 eV light causes readily visible blue lumines-
cence, but no additional absorption bands are produced. Harris et al.
[134]
reported
the absorption coefficients of BSO crystals doped with V, Cr, Mn, and so on. They
conclude that the hydrothermal material shows special promise for optical “tailor-
ing,” since the native Czechrolski defect is absent and photoconductive sites and
traps may be introduced by doping without interference from this defection. Leigh
et al.
[135]
reported the characterization of Czechrolski and hydrothermally grown
BSO crystals. They have observed significantly smaller optically and thermally
induced conductivities in the hydrothermal material. A lower defect content also
appears to inhibit the conduction processes for the hydrothermal material in terms
of missing traps responsible for a hopping conduction process. Slightly higher con-
centrations of Fe and V were found in the hydrothermal material, but these impurities
do not affect the color or contribute to a 500 nm absorption in this material.
However, an equivalent concentration of these impurities in the Cz-grown material
from a hydrothermal charge does affect both the absorption and the thermally stimu-
lated current Thermally Stimulated Current (TSC) results. Thus, the near-intrinsic
BSO can be prepared using hydrothermal growth techniques.
There are several other reports dealing with the study of phase formations in
related systems giving compounds isostructural to BSO. For example, Surnina and
Litvin
[136]
have studied the phase formation in the system Na
2
O
a
Me
2
O
3
a
Bi
2
O
3
a
Al, Ga, In) under hydrothermal conditions. Abrahams et al.
[137]
obtained Bi
12
GeO
20
(BGO) crystals, germanium sillenite, which exhibit simi-
lar properties. The other commonly used cations substituting for Si are Al, Ga, Fe,
Ge, and Ti.
H
2
O (Me
5
