The development of frequency-conversion technology in the infrared region is in urgent need of new excellent infrared nonlinear optical (IR NLO) materials. How to achieve a good balance between laser damage threshold (LDT) and NLO coefficient (dij) for new IR NLO candidates is still a challenge. The combination of the highly electropositive alkali metal (Na) and Zn with d(10) electronic configuration into crystal structure affords one new IR NLO material, Na2ZnGe2S6. It exhibits excellent properties including a wide transparent region (0.38-22 μm), large band gap (3.25 eV), and especially a balance between a strong NLO coefficient (30-fold that of KDP) and a high LDT (6-fold that of AgGaS2), indicating a promising application in the IR region. Moreover, novel common-vertex-linked wavelike ∞[GeS3]n chains are interestingly discovered in Na2ZnGe2S6, which rarely exist in the reported thiogermanides containing alkali metals. In addition, calculated SHG density and dipole moment demonstrate that the large NLO response is mainly attributed to the cooperative effects of the [GeS4] and [ZnS4] units.

Infrared nonlinear optical (IR NLO) materials with excellent performances are particularly important in laser technology. However, to design and synthesize an efficient IR NLO material with a balance between the optical band gap and the NLO coefficient is still a huge challenge. With this in mind, four new IR NLO materials Na2 BaSnS4 , Na2 BaSnSe4 , Na2 BaGeS4 , and Na2 BaGeSe4 were successfully designed and synthesized. The compounds exhibit excellent properties with a suitable balance of band gap and NLO coefficient measured for Na2 BaSnS4 (3.27 eV and about 17×KDP, that is, about 17 times that of KH2 PO4 (KDP)) and Na2 BaGeS4 (3.7 eV and about 10×KDP), demonstrating that the systems satisfy the key requirements as promising IR NLO candidates. Remarkably, the new compounds also undergo a novel structural transformation from tetragonal to trigonal systems, the first time that this has been reported for quaternary metal chalcogenides.

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A new family of noncentrosymmetric isostructural compounds, Na2Hg3M2S8 (M = Si, Ge, and Sn), was successfully synthesized. They crystallize in the tetragonal space group P4̅c2 with Z = 2. Their major structures are composed of infinite cross-connected ∞ (HgS3) n chains and isolated [MS4] ligands and show the interesting tunnel features. Interestingly, compared with the structures of A2Hg3M2S8 (A = alkali metal, Na–Cs), it can be found that the structural symmetries show a gradually rising tendency from Cs to Na analogues as a result of cation size effect, which rarely exists in quaternary alkali metal chalcogenides. Property measurements show that title compounds exhibit strong second harmonic generation (SHG) effects with a phase-matching behavior at 2.09 μm, wide transparency range in the infrared (IR) region, and large laser-damage thresholds (LDTs). Remarkably, Na2Hg3Si2S8 and Na2Hg3Ge2S8 achieve the suitable balance between large SHG effects (1.3 and 2.2 × benchmark AgGaS2) and high LDTs (4.5 and 3 × AgGaS2), respectively, and can be expected to be potential nonlinear optical (NLO) candidates in the IR region. Moreover, band structures and NLO properties of title compounds are also theoretically studied, and the calculated NLO coefficients are consistent with the experimental observations.

Chalcopyrite-type AgGaQ (Q = S, Se) and ZnGeP are the main commercial infrared nonlinear optical (IR NLO) crystals. Unfortunately, performance defects including low laser damage threshold (LDT), harmful two-photon absorption (TPA), or small birefringence limit their application. With this background, four new compressed chalcopyrite-like IR NLO materials LiBaMQ (M = Ge, Sn; Q = S, Se) were successfully synthesized with the typical AgGaQ as templates. Remarkably, LiBaGeS and LiBaSnS not only maintain the good NLO responses (0.5 and 0.7 × AgGaS) but also overcome low LDTs and TPA of commercial chalcopyrites, demonstrating that they satisfy critical demands as promising IR NLO candidates. All of them exhibit phase-matching abilities. Furthermore, the discovery of chalcopyrite-like compounds also provides a feasible design strategy to explore new promising IR NLO materials.

N onlinear optical (NLO) crystals are of great importance in producing coherent ultraviolet−visible (UV−vis), deep-UV (DUV), or infrared (IR) light sources for civil and military applications by frequency-conversion technology. 1−23 Borates are widely applied as short-wave NLO materials because of their large bandgaps and high laser damage threshold that originate from strongly covalent B−O bonds in [BO 3 ] 3− and [BO 4 ] 5− anionic groups, such as β-BaB 2 O 4 , 1 LiB 3 O 5 , 2 KBe 2 BO 3 F 2 , 3 etc.; unfortunately, they cannot be used in the IR region because of absorption resulting from their B− O vibration modes which limits the infrared transmission. Meanwhile, chalcogenides, 6 owing to its wide optical transmission range and strong NLO response, are wildly researched for IR NLO materials. Recently, in view of the performance drawbacks (low laser damage threshold (LDT) and harmful two photon absorption) of commercial IR NLO materials, 24−26 it is urgent to explore new excellent IR NLO materials 27−33 with suitable balance between wide bandgap (E g ≥ 3.0 eV) and large second harmonic generation (SHG) effect (NLO coefficient d ij ≥ 0.5 × benchmark AgGaS 2 ). 34

A series of new metal chalcongenides, BaCdSnSe4 (1), Ba2SnSe4 (2), Mg2GeSe4 (3), and Ba2Ge2S6 (4), were successfully synthesized for the first time. Among them, compounds 2 and 4 were prepared by a molten flux method with Zn as the flux. In their structures, all of them have MQ4 (M = Sn, Ge; Q = S, Se) units. For compound 1, the CdSe4 and SnSe4 groups are connected to form CdSnSe6 layers and these layers are linked together by the Ba atoms. Compounds 2 and 3 are composed of isolated MSe4 (M = Sn, Ge) units and charge-balanced by the Ba or Mg atoms, respectively, while compound 4 has infinite ∞(GeS3)n chains, which is different from the structures of the other three compounds that only have isolated MSe4 (M = Sn, Ge) units. The measured IR and Raman data of the title compounds show wide infrared transmission ranges. The experimental band gaps of compounds 1, 2, 3 and were determined to be 1.79, 1.90, and 2.02 eV, respectively. Band structures were also calculated and indicate that their tetrahedral units, such as [SnSe4], [GeS4] and [GeSe4], determine the energy band gaps of the title compounds, respectively. As for compound 1, based on fundamental light at 2.09 μm, the experimental second harmonic generation (SHG) response is about 1.6 times that of the benchmark AgGaS2, which is also consistent with the calculated value. Based on the above results, compound 1 has promising applications in the IR field as a NLO material.

Cluster of differentiation 44 (CD44), a well-known transmembrane glycoprotein, serves as a promoting factor in the carcinogenesis and progression of a variety of neoplasms. Previous studies have demonstrated that aberrant expression of CD44 was associated with the initiation, invasion, metastasis, and therapy-resistance of breast cancer, but whether there was any association between CD44 and pathological characteristics of breast cancer or epidermal growth factor receptor (EGFR) has not been clearly elucidated. In this study, we utilized public microarray data analysis and tissue microarray technologies to display that CD44 level was enhanced in breast cancer and was significantly correlated with histological grade and the status of estrogen receptor, progesterone receptor and human epidermal growth factor receptor-2 (HER2) and EGFR. Furthermore, mRNA expression of CD44 in breast tumors was positively correlated with basal cytokeratin markers KRT5 and KRT17, but inversely associated with luminal marker FOXA1. Besides, Kaplan-Meier analysis showed that high CD44 mRNA level had adverse impact on the progression-free survival of patients with HER2-expressing or basal-like breast cancer. Functionally, inhibition of EGFR activity by erlotinib impaired the invasion and migration ability of breast cancer cell lines. Western blot assays demonstrated that erlotinib treatment decreased the expression of CD44, accompanied with the reduced protein levels of mesenchymal and cancer stem cell markers. Collectively, this study suggested that the expression of CD44 was upregulated by EGFR pathway and CD44 had a robust impact on the development of breast cancer.