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