Inorg. Chem. 2008, 47, 2362-2367
Characterization and Properties of Novel Infrared Nonlinear Optical
Crystal CsGe(BrxCl1-x)3
Zhi-Guang Lin,*,† Li-Chuan Tang,‡ and Chang-Pin Chou†
Department of Mechanical Engineering, National Chiao Tung UniVersity,
Hsinchu 305, Taiwan, R.O.C., and Department of Electrical Engineering, Chung-Cheng Institute
of Technology, National Defense UniVersity, Taoyuan 353, Taiwan, R.O.C
Received June 24, 2007
Innovative infrared nonlinear optical crystals CsGe(BrxCl1-x)3 were synthesized. Their powder X-ray diffraction patterns
indicated that they had rhombohedral structures with (R3m, No. 160) space group symmetry. Their structural distortion
increased with x. The Kurtz powder techniques revealed that the nonlinear optical efficiency of CsGeBr3 is about
9.64 times larger than that of rhombohedral CsGeCl3 and 28.29 times larger than that of KH2PO4 (KDP); most
importantly, CsGe(BrxCl1-x)3 is phase-matchable. The transparent infrared spectrum of rhombohedral CsGe(BrxCl1-x)3
was extended to over 30 µm and demonstrated its potential in the field of nonlinear optics and applicability in the
infrared region.
1. Introduction
ZnGeP2,1,10 Tl3AsS3,11 and Tl3AsSe3.12 Although these
crystals seem to exhibit appropriate nonlinearity, they either
are difficult to produce or have low optical damage thresh-
olds,13–15 since their bandgaps are narrow. Hence, the search
for new infrared NLO crystals with excellent properties,
especially a high damage threshold, has become a key area
of research in NLO material science and laser technology.1
Various ternary halides, such as ABX3 (A ) Cs; B ) Ge;
X ) Cl, Br, or I),16–18 have been discovered to exhibit
Frequency conversion is an essential technique for extend-
ing laser frequency ranges. Nonlinear optical (NLO) crystals
are indispensable in applying this approach in an efficient
frequency-shifting device. Several useful crystals, such as
KH2PO4 (KDP), LiNbO3, KTiOPO4 (KTP), ꢀ-BaB2O4 (BBO),
and LiB3O5 (LBO),1 have been discovered and successfully
utilized for converting laser frequencies into visible and
ultraviolet radiation, but they are not transparent in the mid-
infrared region. Lack of material transparency in the mid-
infrared region is not the only obstacle. Other factors such
as the absence of a center of symmetry and a high optical
damage threshold2 are also problematic. Therefore, alterna-
tive materials have been developed. They include compound
semiconductors such as GaSe,3,4 AgGaS2,5–8 AgGaSe2,9
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* Author to whom correspondence should be addressed. Tel: 886-3-
5712121-55157. Fax: 886-3-5720634. E-mail: zglin.me91g@nctu.edu.tw.
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†
National Chiao Tung University.
National Defense University.
‡
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2362 Inorganic Chemistry, Vol. 47, No. 7, 2008
10.1021/ic7011777 CCC: $40.75 2008 American Chemical Society
Published on Web 03/05/2008