Polycrystal Synthesis, Crystal Growth, Structure, and Optical Properties of AgGaGe_nS_2(n+1) (n = 2, 3, 4, and 5) Single Crystals for Mid-IR Laser Applications

Abstract

AgGaGe n S2(n+1) crystal is a series of quaternary nonlinear optical materials for mid-IR laser applications of converting a 1.064 μm pump signal (Nd:YAG laser) to 4–11 μm laser output, but only AgGaGeS4 has attracted the most attention, remaining the other promising AgGaGe n S2(n+1) crystal whose physicochemical properties can be modulated by n value. In this work, AgGaGe n S2(n+1) (n = 2, 3, 4, and 5) polycrystals are synthesized by vapor transport and mechanical oscillation method with different cooling processes. High-resolution X-ray diffraction analysis and refinement have revealed that all the four compounds are crystallized in the noncentrosymmetric orthorhombic space group Fdd2, resulting in the excellent nonlinear optical property, and the distortion of tetrahedron with the variation of n value causes the discrepancy of physicochemical property. Besides, using the modified Bridgman method, AgGaGe n S2(n+1) single crystals with 15 mm diameter and 20–40 mm length have been grown. We have discussed the structure and composition of AgGaGe n S2(n+1) by XPS spectra and analyzed the three kinds of vibration modes of tetrahedral clusters by the Raman spectra. The Hall measurement indicates that the AgGaGe n S2(n+1) single crystals are p-type semiconductor, and the carrier concentration decreases with the increasing n value. All the transmittances of as-grown AgGaGe n S2(n+1) samples exceeds 60% in the transparent range, especially the transmittance of AgGaGe2S6, is up to 70% at 1064 nm, and the band gap of as-grown crystal increases from 2.85 eV for AgGaGe2S6 to 2.92 eV for AgGaGe5S12. After a thermal annealing treatment, the absorptions at 2.9, 4, and 10 μm have been eliminated, and the band gap changed into the range of 2.89–2.96 eV.

Investigation of the Anisotropic Thermal Expansion Mechanism of AgxGaxGe1–xSe2 Crystals

“…The compounds of the Ag x Ga x Ge 1– x Se 2 were regarded as new γ-type solid solutions in the AgGaSe 2 -GeSe 2 phase diagram . The structure of the Ag x Ga x Ge 1– x Se 2 ( x = 0.25, 0.167) determined by the powder X-ray diffraction method belongs to Fdd 2 space group which is similar to that of AgGaGeS 4 . , Such a structure is associated with its ternary compound, for instance, the structure of LiGaGe 2 S 6 crystal (orthorhombic, Fdd 2) derived from LiGaS 2 , but they also have slight difference . The evolution process from AgGeSe 2 to Ag x Ga x Ge 1– x Se 2 is shown in Figure .…”

Non-stoichiometry and point native defects in non-oxide non-linear optical large single crystals: advantages and problems

“…With the accumulated experience in the synthesis of AGGS crystals, this team focused on growing AgGaGeS 4 · n GeS 2 ( n = 2–4) crystals having also good non-linear properties ( d 31 ∼ 13.8 pm V −1 ) and suitable birefringence for phase matching. 33 To introduce a larger amount of GeS 2 , a special two-zone rocking furnace was used and more attention was given to the cooling process to provide completeness of entering the volatile component. All the crystals as-grown by a modified B method from high-quality polycrystalline materials were related to members of one solid solution, as based on the detailed structural (XRD, Raman spectra) and compositional (EDS, XPS) characteristics.…”

“…63,68 Since the actual Li losses are always unpredictable and the Li vapor confinement inside an absolutely inert crucible is an unresolved problem, the spatial, chemical and phase homogeneity of the polycrystalline materials should be examined by more precise and sensitive methods. We believe that both optical characterization via laser beam perturbations 33 as well as the DD method 56,59 detecting the phase inhomogeneity at a microscale level can cope well with this task. In practice, DD analysis has already been used to identify impurity phases and their spatial distribution in crystals.…”

Homogeneity characterization in AgGaGeS4, a single crystal for nonlinear mid-IR laser applications

“…Thus, there is a lack of material appropriate for high power applications in the entire middle infrared range. Recently, AgGaGeS4 crystal has shown interesting properties with a wider transparency range than ZnGeP2 (0.5 to 11.5 µm), a good nonlinear coefficient (d31 = 15 pm.V -1 ) [31] and a low residual absorption coefficient (0.05 cm -1 ) at 1.064 µm making it suitable for a Nd:YAG laser pumping. Moreover, this material has shown a higher laser damage threshold than AgGaS2, 50 MW.cm -2 at 1.064 µm (τ= 10 ns) [32], 73 MW.cm -2 at 2.05 µm (τ =15 ns; 10 kHz) [33] and 230 MW.cm -2 (τ =30 ns) at 9.55 µm [34], making it promising for applications above the current power limitation of AgGaS2 and AgGaSe2.…”

“…Recently, several works were focused on improving polycrystalline synthesis, crystal growth and annealing conditions of the AgGaGeS4 crystal [43,44,48,49,50,51]. In the present work, a new approach is proposed in complement to these works to assess the quality of an AgGaGeS4 single crystal grown by the Bridgman-Stockbarger method.…”