AgGaSe₂-Inspired Nonlinear Optical Materials: Tetrel Selenides of Alkali Metals and Mercury

Abstract

High-performance infrared nonlinear optical (IR NLO) materials are crucial devices in tunable IR solid-state lasers, and the functional-group cosubstitution strategy was selected to design and explore outstanding IR NLO crystals. For that reason, taking the famous AgGaSe 2 as the template, five new mercury-based IR NLO selenides, Li 2 HgMSe 4 and Na 2 Hg 3 M 2 Se 8 (M = Si, Ge, Sn), were successfully designed and synthesized through concurrently replacing the cation (Ag + ) and GaSe 4 unit with the alkali metal (Li + or Na + ) and anionic groups (HgSe 4 and MSe 4 ) to optimize crystal structures and performances. All of them exhibit extremely strong powder second-harmonic generation (SHG) responses (3.6−6.0 × commercial AgGaS 2 ) with the essential phase-matching behavior. Note that Li 2 HgSnSe 4 exhibits the largest SHG response (6.0 × AgGaS 2 ) among the known Hg-based chalcogenides without disorder structures, and its millimeter-level single-crystals were successfully grown by the Bridgman method. Theoretical analysis further illustrates that the different arrangement modes of HgSe 4 units offer considerable but distinguishing SHG contributions, such as Li 2 HgMSe 4 (53−55%) and Na 2 Hg 3 M 2 Se 8 (19−23%). This research result highlights the practicability of the functional group cosubstitution-oriented design strategy and Hg-based selenides could be viewed as the optimal system for future exploration of large SHG crystals.

Phase Competition and Strong SHG Responses of the Li2MIIMIVSe4 Family: Atom Response Theory Predictions versus Experimental Results

“…Among them, all three structures of LHSnSe exhibit the largest d eff p in this family, ∼22.7 pm/V, which is ∼2.4 times that of AGS. We note that, during the preparation of our manuscript, LHSnSe and LHGSe having the Pna 2 1 structure were experimentally synthesized, proving the reliability of our prediction. It should be mentioned that it is inappropriate to compare the calculated effective SHG responses directly with the experimental reported ones as the experimental values of Pna 2 1 -LHSnSe and Pna 2 1 -LHGSe were obtained at the wavelength (2.09 μm) which falls out of the phase matching wavelength range for AGSe (3.1–12.8 μm) .…”

d6versus d10, Which Is Better for Second Harmonic Generation Susceptibility? A Case Study of K2TGe3Ch8 (T = Fe, Cd; Ch = S, Se)

“…Many factors, such as band gap, absorption coefficient, thermal conductivity, and thermal expansion coefficient, contribute to the LDTs of solids . As summarized in Table S6, many small band gap selenides exhibit high LDTs and high SHG. − K 2 CdGe 3 S 8 is a promising candidate for infrared NLO material, which combines suitable band gap, good stability, high SHG intensity, high LDTs, and type-I phase-matching behavior. One interesting question raised here would be why K 2 CdGe 3 S 8 shows a much better SHG response than K 2 FeGe 3 S 8 regardless of their isostructural nature.…”

The Antiperovskite‐Type Oxychalcogenides Ae3Q[GeOQ3] (Ae = Ba, Sr; Q = S, Se) with Large Second Harmonic Generation Responses and Wide Band Gaps

“…Nonlinear optical (NLO) crystals are widely concerned due to their ability to expand the output spectral range of laser sources based on frequency conversion technology. [ 1 ] During the past several decades, many excellent NLO crystals have been discovered, such as LiB 3 O 5 (LBO), [ 2 ] β ‐BaB 2 O 4 (BBO), [ 3 ] KH 2 PO 4 (KDP) [ 4 ] and KTiOPO 4 (KTP). [ 5 ] However, in the infrared (IR) region, only AgGaS 2 (AGS), [ 6 ] AgGaSe 2 (AGSe) [ 7 ] and ZnGeP 2 (ZGP) [ 8 ] are commercialized and they contain some intrinsic drawbacks, such as low laser damage threshold (LDT) and two‐photon absorption (TPA), which prohibit their applications in high‐power conditions.…”

“…[ 9 ] Therefore, it is still urgent to explore new IR nonlinear optical (NLO) crystals with excellent performance. [ 1 , 10 ] For an IR NLO crystal, the crystallographically non‐centrosymmetric (NCS) structure is the prerequisite because only NCS structures can exhibit second‐order NLO properties. Beyond this, some harsh functional properties are necessary for the application of IR NLO crystals, including: i) high second‐harmonic generation (SHG) coefficient; ii) large band gap ( E g ); iii) appropriate birefringence (Δ n ); iv) broad transmission window; and v) favorable physical and chemical stability and crystal growth habit.…”