The effect of LaBr3:Ce aliovalent co-doping on its mechanical strength
A. Benedetto*, S. Valladeau*, D. Richaud+, V. Ouspensky*, R. Gy* Saint-Gobain Recherche, Aubervilliers, France *
Saint-Gobain Crystals, Nemours, France+ Introduction
Lanthanum bromide cerium doped single crystal is a
transparent scintillator material that offers outstanding
scintillation properties with high light yield, excellent energy
resolution, fast emission and excellent proportionality.
Although properly packaged detectors are robust enough to
withstand operating conditions during geophysical oil logging
operations, the material itself is brittle and exhibits low
fracture toughness [1].
Objective
Aliovalent co-doping may increase the
toughness of LaBr3:Ce single crystals [2] and
thus results in improved resistance to thermo-
mechanical shocks.
The objective of the present work was to verify
experimentally if aliovalent co-doping, at levels
that do not negatively impact crystal growth,
can be a good solution to increase the overall
mechanical resistance of LaBr3:Ce single
crystals.
Codoped crystals
Co-doping was obtained by adding the studied
co-doping element in the melt growth bath
Codoping element
Bath
concentration
(ppm)
Crystal
concentration
(ppm)
Sr 232 21 – 28
Sr 1832 90 – 184
Ca 207 9 – 16
Zn 290 < 3
Hf 618 < 4
Zr 383 < 1,5
Mechanical strength by 4-points bending
45 mm
15 mm
Experiments performed in a dry-box under nitrogen atmosphere (dew point < -85 °C)
Fracture surfaces
(a-axis samples)
Fracture surface
(c-axis samples)
Microindentation
25 gf
100 µm
500 gf
200 µm
2 kgf 2 kgf 2 kgf 2 kgf 2 kgf 2 kgf 2 kgf
2 kgf
2 kgf
2 kgf
300 gf 500 gf
1 kgf
1 kgf
1 kgf
a
c H
E
c
PKc
018.00
02
3
Mechanical load
Length of radial cracks at the surface
Young modulus
Hardness
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
1,8
2,0
2,2
220
240
260 280
300
320
340
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
1,8
2,0
2,2
Ca codoped
CeBr3
LaBr3 standard
Sr codoped
proportional to KC
(MPa m-1/2
)
[3]
Experiments performed in a dry-box under nitrogen atmosphere (dew
point < -85 °C) on polished unhydrated and unoxidized surfaces.
Conclusions
Aliovalent co-doping did not result in a measurable increase in the mechanical strength of
LaBr3:Ce single crystals.
• The effective co-doping level that can be attained inside the crystals is quite low (<200 ppm)
• The toughness of the materials is not affected in a significant way by the aliovalent co-doping
We anticipate that the effect of aliovalent co-coping will be the same for other alkali halide
materials such as LaCl3 and CeBr3.
[1] Findley, K. O., Johnson, J., Bahr, D. F., Doty, F. P., & Frey, J. (2007, September). Fracture
and deformation behavior of common and novel scintillating single crystals. In Proceedings of
the SPIE (Vol. 6707, pp. 670706-1).
[2] Harrison, M. J., & Doty, F. P. (2007, September). Initial investigation of strengthening
agents for lanthanide halide scintillators. In Optical Engineering+ Applications (pp. 67070B-
67070B). International Society for Optics and Photonics.
[3] Lawn, B. (1993). Fracture of brittle solids. Cambridge university press.
References
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