New inorganic nonlinear-optical (NLO) materials are necessary for solid-state lasers to generate coherent radiation in the ultraviolet (UV) and deep-UV regions. The purpose of this Viewpoint is to ...describe the chemical and physical requirements for such materials, as well as the current state of the field. In addition, the “birefringence challenge” is described and a flowchart is presented for characterizing new second-harmonic-generation materials. Finally, several new materials are suggested that may have UV and/or deep-UV NLO applications.
Inorganic materials exhibiting second-harmonic generation (SHG) are used to generate coherent radiation at wavelengths where solid-state laser sources are not available; that is, the deep UV (DUV) ...below 200 nm. Here, we describe the structure and optical property requirements that should be assessed to conclusively demonstrate the discovery of a functional DUV material for nonlinear optical (NLO) applications.
Discovering new deep‐ultraviolet (DUV) nonlinear optical (NLO) materials is currently a great challenge. The reported DUV NLO materials are almost exclusively borates or phosphates. Silicates—the ...largest constituent of the earth's crust—are excluded owing to their weak second harmonic generation (SHG) response. We report a silicate, Li2BaSiO4, with edge‐sharing LiO4–SiO4 tetrahedra that achieves the balance between a short UV absorption edge, below 190 nm, and a large SHG response, 2.8×KDP. The SHG intensity is the largest for silicates without second‐order Jahn–Teller cations, and exceeds that of non‐isomorphic Li2SrSiO4 by more than an order of magnitude. As such Li2BaSiO4 may be seen as a promising DUV‐UV NLO material. This research indicates that edge‐sharing tetrahedra is a new design parameter for discovering new DUV NLO materials.
Meet on the edge: Silicates are not usually deep UV nonlinear optical (DUV NLO) materials owing to their weak second harmonic generation (SHG) response. A silicate, Li2BaSiO4, with edge‐sharing LiO4–SiO4 tetrahedra is now shown to have a large SHG response, 2.8×KDP. As such, Li2BaSiO4 is a promising DUV‐UV NLO material. Edge‐sharing tetrahedra is a new design parameter for discovering new DUV NLO materials.
Borate halides are an ideal materials class from which to design high‐performance nonlinear optical (NLO) materials. Currently, borate fluorides, chlorides, and bromides are extensively investigated ...while borate iodide materials discovery remains rare because of the perceived synthetic challenges. We report a new borate iodide, Pb2BO3I, synthesized by a straightforward hydrothermal method. The Pb2BO3I chemical formula conceals that the compound exhibits a structure similar to the well‐established KBe2BO3F2 (KBBF), which we show supports the highest second‐harmonic generation (SHG) at 1064 nm in the KBBF family, 10 × KH2PO4 (KDP), arising from the inclusion of Pb2+ and I− and the crystal chemistry. Our work shows that KBBF‐related compounds can be synthesized incorporating iodide and exhibit superior NLO responses.
I've got my I on you: A new borate iodide, Pb2BO3I, is prepared for nonlinear optics applications by a straightforward hydrothermal method. It has a similar structure to KBe2BO3F2 (KBBF) and the highest second‐harmonic generation (SHG) in the KBBF family. Calculations show this SHG response arises from the inclusion of Pb2+ and I− ions.
A new deep-ultraviolet nonlinear optical material, RbMgCO3F, has been synthesized and characterized. The achiral nonpolar acentric material is second harmonic generation (SHG) active at both 1064 and ...532 nm, with efficiencies of 160 × α-SiO2 and 0.6 × β-BaB2O4, respectively, and exhibits a short UV cutoff, below 190 nm. RbMgCO3F possesses a three-dimensional structure of corner-shared Mg(CO3)2F2 polyhedra. Unlike other acentric carbonate fluorides, in this example, the inclusion of Mg2+ creates pentagonal channels where the Rb+ resides. Our electronic structure calculations reveal that the denticity of the carbonate linkage, monodentate or bidendate, to the divalent cation is a useful parameter for tuning the transparency window and achieving the sizable SHG response.
Balancing the wide band gap, large second harmonic generation (SHG) response, and moderate birefringence are significant but addressable challenges for designing nonlinear optical (NLO) materials. ...Based on the band-gap engineering in perovskite solar cell materials, we have successfully synthesized a new fluorotellurite, BaF2TeF2(OH)2, which exhibits a pseudo-Aurivillius structure and crystallizes in a noncentrosymmetric and polar space group Pmn21. The physical property measurements show that this material can effectively balance the requirements among the short UV absorption edge (∼205 nm), large SHG response (∼3 × KDP) and moderate birefringence (∼0.078@350–700 nm) and is a promising ultraviolet NLO crystal.
Noncentrosymmetric mixed-metal carbonate fluorides are promising materials for deep-ultraviolet (DUV) nonlinear optical (NLO) applications. We report on the synthesis, characterization, ...structure–property relationships, and electronic structure calculations on two new DUV NLO materials: KMgCO3F and Cs9Mg6(CO3)8F5. Both materials are noncentrosymmetric (NCS). KMgCO3F crystallizes in the achiral and nonpolar NCS space group P6̅2m, whereas Cs9Mg6(CO3)8F5 is found in the polar space group Pmn21. The compounds have three-dimensional structures built up from corner-shared magnesium oxyfluoride and magnesium oxide octahedra. KMgCO3F (Cs9Mg6(CO3)8F5) exhibits second-order harmonic generation (SHG) at both 1064 and 532 nm incident radiation with efficiencies of 120 (20) × α-SiO2 and 0.33 (0.10) × β-BaB2O4, respectively. In addition, short absorption edges of <200 and 208 nm for KMgCO3F and Cs9Mg6(CO3)8F5, respectively, are observed. We compute the electron localization function and density of states of these two compounds using first-principles density functional theory, and show that the different NLO responses arise from differences in the denticity and alignment of the anionic carbonate units. Finally, an examination of the known SHG active AMCO3F (A = alkali metal, M = alkaline earth metal, Zn, Cd, or Pb) materials indicates that, on average, smaller A cations and larger M cations result in increased SHG efficiencies.
Birefringent materials are widely used in various advanced optical systems, owing to their vital role in creating and controlling polarized light. Currently, Sn2+‐based compounds containing ...stereochemically active lone‐pair (SCALP) cations are extensively investigated and considered as one class of promising birefringent materials. To solve the problem of relatively narrow bandgap of Sn2+‐based compounds, alkali metals and multiple halogens are introduced to widen the bandgap during the research. Based on this strategy, four new Sn2+‐based halides, A2Sn2F5Cl and ASnFCl2 (A = Rb and Cs), with large birefringence, short ultraviolet (UV) cutoff edge, and wide transparent range are successfully found. The birefringences of A2Sn2F5Cl (A = Rb and Cs) are 0.31 and 0.28 at 532 nm, respectively, which are among the largest in Sn‐based halide family. Remarkably, A2Sn2F5Cl possess relatively shorter UV cutoff edge (<300 nm) and broad infrared (IR) transparent range (up to 16.6 µm), so they can become promising candidates as birefringent materials applied in both UV and IR regions. In addition, a comprehensive analysis on crystal structures and structure–property relationship of metal Sn2+‐based halides is performed to fully understand this family. Therefore, this work provides insights into designing birefringent materials with balanced optical properties.
Compounds A2Sn2F5Cl (A = Rb and Cs) combine large birefringence (0.28–0.31 at 532 nm), short UV cutoff edge (<300 nm), and wide transparent region (≈0.28–16.6 µm) together, and these merits make them become the alternative birefringent material candidates for optical applications in the UV–vis–IR region.
A beryllium-free deep-ultraviolet (DUV) nonlinear-optical (NLO) material, K3Sr3Al4Li2B6O20F, has been synthesized and characterized. Unlike KBe2BO3F2 (KBBF), the reported NLO material does not ...require the use of toxic BeO in the synthesis, and through the judicious selection of cations, strong interlayer interactions are observed that facilitate the crystal growth. K3Sr3Al4Li2B6O20F exhibits second-harmonic generation (SHG) at both 1064 and 532 nm with efficiencies of 1.7KH2PO4 and 0.3β-BaB2O4 and has an absorption edge of 190 nm. Because of the strong interlayer interactions, we were able to grow well-faceted large crystals, 8 × 8 × 5 mm3, through a top-seeded-solution-growth technique. With these crystals, we determined a birefringence of 0.0574 at 1064 nm and a type I phase-matching SHG limit of 224 nm.
A new ultraviolet nonlinear optical (NLO) material, Pb3Mg3TeP2O14 (PMTP), has been synthesized and characterized. The chiral material exhibits a large second harmonic generation (SHG) response of ...13.5 × KDP (600 × α-SiO2), and the shortest absorption edge (250 nm) of reported materials with a strong SHG response (>10 × KDP). PMTP has a three-dimensional crystal structure of corner-shared MgO4, PO4, and TeO6 polyhedra, which form a TeMg3P2O14∞ framework. Electronic structure calculations revealed that the stereoactive lone pair on the Pb2+ cation is critical to producing the substantial NLO response and that the NLO activity is further enhanced by the presence of triply bidentate Te6+ cations found in Te–O–O–Pb rings.
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