From Ba₃Nb₂O₂F₁₂(H₂O)₂ to Ba_0.5NbO₂F₂(H₂O): Achieving Balanced Nonlinear Optical Performance by O/F Ratio Regulation

Abstract

Metal oxyhalides have attracted extensive attention as fascinating nonlinear optical (NLO) materials. Here, two barium niobium oxyfluorides, Ba3Nb2O2F12(H2O)2 (1) and Ba0.5NbO2F2(H2O) (2), have been obtained by regulating the O/F ratio in Nb–O–F units (NbOF6 pyramids to NbO4F2 octahedra). The overall NLO effect is improved from 1 to 2 with larger second-harmonic generation (SHG) intensities (0.9 to 1.7 × KH2PO4 (KDP)) and maintainable large band gaps (>3.0 eV) by regulating the O/F ratio in Nb–O–F units (1:6 to 4:2).

From ZnF2 to ZnF2(H2O)4: Partial Substitution Achieves Structural Transformation and Nonlinear Optical Activity while Keeping Short Ultraviolet Cutoff Edge

“…Here, we chose ZnF 2 as the parent compound. On the one hand, fluorides tend to have a large band gap, corresponding to a low UV cutoff wavelength due to the largest electronegativity of F atom. − On the other hand, the polyhedron of Zn 2+ with d 10 electron configuration is prone to second-order Jahn–Taylor distortion, which is more likely to form an NCS structure, and then produce the SHG effect. − In addition, based on previous reports, we also know that Zn-containing oxyhalides mostly reach short UV cutoff edges. Such compounds as RbZn 2 BO 3 Br 2 (214 nm), KZn 2 BO 3 Cl 2 (194 nm), and NH 4 Zn 2 BO 3 Cl 2 (190 nm) were reported to confirm this idea.…”

Li13YGe4O16: A Mid-infrared Rare-Earth Germanate Nonlinear Optical Crystal Featuring a Broad Transmission Range and an Enlarged Band Gap

“…For instance, data derived from the Inorganic Crystal Structure Databases (ICSD) demonstrate that the majority of germanate-based inorganic compounds exhibit a propensity to crystallize more readily in centrosymmetric space groups (Table S1 In the Supporting Information), thereby impeding their potential for fabrication as NLO crystals. , Therefore, the pursuit and exploration of innovative high-performance functional materials exhibiting noncentrosymmetric structures within the germanate system is evident topical. To achieve an acentric structure, a common design approach is to incorporate second-order Jahn–Teller (SOJT) distorted cations like Mo 6+ , V 5+ , Bi 3+ , and Pb 2+ , etc. − Unfortunately, the introduction of these heavy elements frequently results in a red shift of the ultraviolet cutoff edge, accompanied by a decrease in the band gap. Previous studies have demonstrated that rare-earth cations bound to oxygen display flexible polyhedral configurations and are susceptible to local environmental distortion, which can be advantageous in the formation of compounds with noncentrosymmetric structures.…”

Hg3O2(NO3)F: a mercury nitrate oxyfluoride with an unprecedented [(Hg3O2F)+]∞cationic framework and excellent optical anisotropy

“…48,49 It follows that the incorporation of halogen anions in nitrates enriches the structure diversity and can provide more promising optical materials. While, based on the survey of nitrates containing halogen atoms, intensive investigations have been performed on compounds comprising metal cations (Pb 2+ , Sn 2+ , Sb 3+ ) with lone pair electrons, which is beneficial for achieving favorable SHG effects and optical anisotropy, 28,39,45 other metal cations including d 0 and d 10 metals which can also produce large polarizability have been less explored. Hence, further explorations are necessary for nitrate halides.…”

“…The combination of two or more kinds of anion groups to design compounds with interesting structure types is a favorable and fruitful route. 1–32 These new crystals may synergize the properties of multiple anions and can be potential candidates in some application fields including birefringence, nonlinear optics, fluorescence, and catalysis. Based on the structure performance relationship, many research systems focusing on optical performance have been developed in recent years.…”