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Updated: Jul 16, 2025
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Published on: April 14, 2020
Evolution of Structures and Optical Properties in a Series of Infrared Nonlinear Optical Crystals LiAg1-InSe2 (0 ≤ x
Lyudmila Isaenko1,2, Linfeng Dong3,4, Ksenia Korzhneva1,2
1Novosibirsk State University, Novosibirsk 630090, Russia.
Abstract:
In this work, a number of new infrared nonlinear optical (NLO) crystals of LiAg1-InSe2, in which the ratio x of Li/Ag varies in a wide range from 0 to 1, are investigated. Structural analysis reveals that the space group of LiAg1-InSe2 evolved from I4̅2d in AgInSe2 to Pna21 in LiInSe2 as x increases from low values (0, 0.2, 0.37) to large values (0.55, 0.78, 0.81, 1). Compared to other Li/Ag coexisting chalcogenides such as LiAg1-GaS2 and LiAg1-GaSe2, the structural distortions in LiAg1-InSe2 are much more prominent. This may explain the limited crystallization region in the phase graph of the tetragonal structure LiAg1-InSe2. The fundamental optical absorption edges in these LiAg1-InSe2 compounds are determined from the direct electronic transitions and the band gaps Eg gradually increase as the lithium content increases, consistent with the first-principles calculations. The composition x = 0.78 is calculated to have a good set of optical properties with a large NLO coefficient (dpowder = 28.8 pm/V) and moderate birefringence (Δn ∼ 0.04). Accordingly, the Li0.78Ag0.22InSe2 crystal is grown by the modified Bridgman-Stockbarger method, and it exhibits a wide transparency range from 0.546 to 14.3 μm at the 2% transmittance level.
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