Crystal growth and thermal annealing of AgGaGe5Se12 crystal

https://doi.org/10.1016/j.jallcom.2020.158002Get rights and content

Highlights

  • AgGaGe5Se12 polycrystalline materials have been synthesized.

  • AgGaGe5Se12 single crystals with Φ30 mm × 50 mm have been obtained.

  • We have discussed the relationship between structure and physicochemical.

  • The absorptions at 3.4 and 7 µm have been eliminated after annealing.

Abstract

AgGaGe5Se12 is a new quaternary nonlinear optical crystal which is applied to laser frequency conversion, especially converting 1.064 µm light to mid-IR range. In this work, we have synthesized the AgGaGe5Se12 polycrystal by the two-zones temperature method. By the modified Bridgman method, we have grown high-quality AgGaGe5Se12 single crystal 30 mm in diameter and 50 mm in length. The structure refinement was carried out by the Rietveld method. Besides, the XRS results were analyzed by comparing with AgGaGeS4 and AgGaGe5S12. In addition, the non-polarized Raman spectra were recorded and the intense peaks were observed at 200 and 232 cm−1. The peaks were attributed to corner-sharing (CS) and edge-sharing (ES) clusters. At last, the crystal was characterized by a high transparency in the 0.6–15 µm spectral range and the absorptions at 3.4 and 7 µm, observed in the as-grown crystal, have been eliminated after annealing. Thus, AgGaGe5Se12 is appropriate for further optical experiments and more comprehensive applications.

Graphical Abstract

AgGaGe5Se12 single crystal is grown by the modified Bridgman method. The structure and physicochemical properties have been discussed.

ga1
  1. Download : Download high-res image (223KB)
  2. Download : Download full-size image

Introduction

The mid-infrared spectral ranges, especially 3–5 µm and 8–12 µm, play an increasingly important role in many applications due to the transparency windows of the atmosphere. The generation of mid-infrared laser illumination mainly depends on available nonlinear optical materials. Therefore, a variety of excellent nonlinear optical materials [1], [2], which are mainly ternary compounds in chalcopyrite structure, have been developed for frequency conversion from near IR to mid-infrared (2–12 µm) spectral range. In recent years, the quaternary nonlinear optical crystals are found to have better performance and have attracted much attention [3]. The series of quaternary crystals such as AgGaGenQ2(n+1) (Q = S, Se), [4], [5], [6] BaGa2GeQ6 (Q = S, Se), [7], [8] Li2Ga2GeS6 [9], [10], LiGaGe2S6 [11], [12], and LiGa(S1−xSex)2 [13], have been prepared to substitute the conventional ternary nonlinear optical crystals, such as AgGaS2, AgGaSe2, BaGa4S7, BaGa4Se7, LiInS2, and LiGaS2. Unlike most of traditional ternary crystals, not only their chemical and physical properties, such as the melting point, band gap and thermal properties, can be regulated by modulating composition, but also, they almost own higher laser damage threshold and it can guarantee the sustainable high-power output. Therefore, they would have more extensive application prospects in mid-infrared laser systems, such as laser guidance, laser counter-measurements, laser medicine and atmospheric monitoring [14]. AgGaGe5Se12 is one of the outstanding representatives of the AgGaGenQ2(n+1) (Q = S, Se) series solid solution crystals. Its promising optical properties, including large nonlinear coefficient (d31 = 28 pm/V) [15], wide spectral region (0.63–16.0 µm) [15], suitable birefringence (0.16) and low absorption (1.064 µm, about 0.01–0.05 cm−1), as well as high laser damage threshold (220 MW/cm2, 1.06 µm, 15 ns) [16], make it suitable for the device fabrication in difference frequency generation (DFG) and second harmonic generation (SHG) [15], [17].

AgGaGenSe2(n+1) crystals were first investigated respectively by Hughes [18] and Badikov et al. [6], and, then, the materials were evaluated again in detail in 1991 [5]. In 2004, Petrov et al. first obtained tunable 4–7.5 µm femtosecond pulses (1 Hz) using difference-frequency mixing [15]. Panyutin [17], Badikov [19] and Knuteson [20] determine the nonlinear coefficient d31 = 25–29 pm/V of AgGaGe5Se12 in second harmonic generation (SHG) experiment and they concluded that the AgGaGe5Se12 crystal may be suitable for the frequency conversion to the mid-infrared range using 1.064 µm pump laser. However, due to the complicated phase equilibria, the large supercooling degree and the higher equilibrium partial pressures, the growth of large-size and high-quality AgGaGe5Se12 crystals suffered from the composition segregation and stomatal inclusion. For instance, Olekseyuk studied the phase equilibria in AgGaSe2-GeSe2 and Ag2Se-Ga2Se3-GeSe2 system [21], [22], [23] to reveal the complicated reaction mechanism. In addition, the AgGaGe5Se12 crystal grown by horizontal gradient freeze method [24] had extremely high scattering losses which would severely restrict its application.

In this work, we synthesized the AgGaGe5Se12 polycrystal using a modified two-zones temperature method [25] and the crystal was analyzed by structural refinement. Then we grew high-quality AgGaGe5Se12 single crystal 30 mm in diameter and 50 mm in length by the Bridgman method. During this process, it is found that the vaporization of GeSe2 results in the composition segregation and stomatal inclusion inside the crystal which seriously affect the quality of AgGaGe5Se12 crystal. Besides, we have analyzed the structure, composition, chemical valence, and lattice vibrational properties by XRD, EDS, XPS and Raman measurements, respectively, and discussed in detail the relationship of the structure and physicochemical property. At last, AgGaGe5Se12 wafer was annealed under the specific conditions and the absorption bands at 3.4 and 7 µm were eliminated.

Section snippets

Polycrystal synthesis and single crystal growth of AgGaGe5Se12

Stoichiometric amounts of high-purity (6 N) liquid Ga, Ag shots, Ge chunks and Se particles (Emei semiconductor high purity material, China) were loaded into a quartz ampoule. Then the quartz ampoule was vacuumed to 1 × 10−4 Pa using a molecular pump, sealed with the use of hydrogen/oxygen flame and put in to a two-zone tube furnace which was kept a little leaning. One side of the furnace was first heated to 650 °C at 100 °C/h, equilibrated for 20 h, and then heated to 960 °C at 90 °C/h,

Result and discussion

The vapor pressure of Se is much lower than that of S and, so, the synthesis of polycrystal AgGaGe5Se12 is not as complicated as that of AgGaGeS4, especially without danger of the explosion caused by high vapor pressure. However, the multi-component reaction is still complicated and difficult to control. Besides, due to the volatile component GeSe2, this compound has high dissociation pressure, easily resulting in composition segregation. In this case, to obtained high-quality AgGaGe5Se12

Conclusions

Using the modified two-zones temperature method we have synthesized the single-phase AgGaGe5Se12 polycrystal. Also, the high-quality AgGaGe5Se12 single crystal with Φ30 mm × 50 mm was grown by the modified Bridgman method. The vaporization of GeSe2 and the macroscopic cluster porosity inside the crystal make up the pivotal issues which seriously affects the AgGaGe5Se12 crystal quality. The crystal composition, structure, lattice vibrations and optical properties were analyzed and discussed in

CRediT authorship contribution statement

Wei Huang: Conceptualization, Methodology, Software, Investigation, Validation, Resources, Writing - Original draft preparation, Writing - Reviewing and Editing. Jun Wu: Data curation. Baojun Chen: Visualization. Jianping Li: Project administration. Zhiyu He: Supervision.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

Project supported by the National Natural Science Foundation of China (Grant No. 51702222), Sichuan science and technology program No. 2019YFG0281, and Natural Science Foundation of Guangdong Province (Grant No. 2017A030310578).

References (31)

Cited by (7)

View all citing articles on Scopus
View full text