AgGaGeSe4: An Infrared Nonlinear Quaternary Selenide with Good Performance

Abstract

The symmetry of crystals is an extremely important property of crystals. Crystals can be divided into centrosymmetric and non-centrosymmetric crystals. In this paper, an infrared (IR) nonlinear optical (NLO) material AgGaGeSe4 was synthesized. The related performance analysis, nonlinear optical properties, and first-principle calculation of AgGaGeSe4 were also introduced in detail. In the AgGaGeSe4 structure, Ge4+ was replaced with Ga3+ and produced the same number of vacancies at the Ag+ position. The low content of Ge doping kept the original chalcopyrite structure and improved its optical properties such as the band gap. The UV-Vis diffuse reflection spectrum shows that the experimental energy band gap of AgGaGeSe4 is 2.27 eV, which is 0.48 eV larger than that of AgGaSe2 (1.79 eV). From the perspective of charge-transfer engineering strategy, the introduction of Group IV Ge elements into the crystal structure of AgGaSe2 effectively improves its band gap. The second harmonic generation (SHG) effect of AgGaGeSe4 is similar to that of AgGaSe2, and at 1064 nm wavelength, the birefringence of AgGaGeSe4 is 0.03, which is greater than that of AgGaSe2 (∆n = 0.02). The results show that AgGaGeSe4 possessed better optical properties than AgGaSe2, and can been broadly applied as a good infrared NLO material.

A Rare Earth Chalcogenide Nonlinear Optical Crystal KLaGeS4: Achieving Good Balance among Band Gap, Second Harmonic Generation Effect, and Birefringence

“…For example, the laser damage threshold is low for AGS (e), and harmful two-photon absorption occurs for ZGP. These drawbacks render significant difficulties to match the pump source. − Therefore, there exists an urgent necessity to explore innovative mid-infrared NLO materials that demonstrate outstanding comprehensive performance, in order to meet the increasing demands in laser-related fields. − …”

Optimal Design of Mid-Infrared Nonlinear-Optical Crystals: From SrZnSnSe4 to SrZnSiSe4

“…The ideal NLO crystal material should have reasonable NLO coefficients and sufficiently large LDTs. − Materials with larger LDTs can withstand more significant laser damage, making them more suitable for practical applications. In general, the LDT effect of materials is highly dependent on their band gap, and a large band gap is beneficial to avoiding double-light absorption as well as to improving the LDT of materials. − Furthermore, the defect-free crystal could be further destroyed by electron excitation to the conduction band and possibly ruined by multiphoton absorption. However, alkali (earth)-metal cations do not undergo a d–d electron leap and have strong ionicity, and their introduction is beneficial to expanding the band gap of materials and further overcoming the defects of MIR NLO materials. − …”