l-Homoproline-Directed Synthesis of Organic-Inorganic Metal Iodides for Second Harmonic Generation

Three organic-inorganic metal iodides, namely, (NH4)(l-hp)ZnI3 (1), [Cd(l-hp)4]Cd3I8 (2), and (l-Hhp)(l-hp)PbI3 (3), have been synthesized using l-homoproline (l-hp) as the structure-directing agent. These compounds feature different noncentrosymmetric structures and optical properties. In particular, compound 3 shows a large second-harmonic-generation response of 3.4 times that of KH2PO4. Density functional theory calculations were performed to gain insight into its structure-property relationship.

From Pb6(HPO3)(H2PO3)Cl9 to Pb6(HPO3)2Br8(H2O)·H2O: Halogen Regulation to Achieve Inorganic Metal Phosphite Halide Nonlinear Optical Material with Unprecedented Pb-Centered Polyhedral Units

Nonlinear optical (NLO) crystals are widely used in various fields. The introduction of lone-pair cations is regarded as an effective strategy to explore NLO crystals. In this work, two novel lead phosphite halides, centrosymmetric Pb6(HPO3)(H2PO3)Cl9 and noncentrosymmetric Pb6(HPO3)2Br8(H2O)·H2O, were obtained via a hydrothermal method. Pb6(HPO3)(H2PO3)Cl9 is the first reported lone-pair metal phosphite with two kinds of phosphite groups (HPO32- and H2PO3-) and Pb6(HPO3)2Br8(H2O)·H2O is the first inorganic NLO phosphite halide with a phase-matchable SHG effect of 1.02 × KDP. In addition, the Pb-centered polyhedral units of PbOCl4, PbOCl6, PbO2Cl5, PbO2Br5, PbOBr6, and PbO3(H2O)Br3 in these two structures have never been reported before. An in-depth study on the structure-property relationship of the two compounds with halogen substitution is also performed.

An Unprecedented [BO2]-Based Deep-Ultraviolet Transparent Nonlinear Optical Crystal by Superhalogen Substitution

Solid-state structures with the superhalogen [BO2]- have thus far only been observed with a few compounds whose syntheses require high reaction temperatures and complicated procedures, while their optical properties remain almost completely unexplored. Herein, we report a facile, energy-efficient synthesis of the first [BO2]-based deep-ultraviolet (deep-UV) transparent oxide K9[B4O5(OH)4]3(CO3)(BO2) ⋅ 7H2O (KBCOB). Detailed structural characterization and analysis confirm that KBCOB possesses a rare four-in-one three-dimensional quasi-honeycomb framework, with three π-conjugated anions ([BO2]-, [BO3]3-, and [CO3]2-) and one non-π-conjugated anion ([BO4]5-) in the one crystal. The evolution from the traditional halogenated nonlinear optical (NLO) analogues to KBCOB by superhalogen [BO2]- substitution confers deep-UV transparency (<190 nm), a large second-harmonic generation response (1.0×KH2PO4 @ 1064 nm), and a 15-fold increase in birefringence. This study affords a new route to the facile synthesis of functional [BO2]-based oxides, paving the way for the development of next-generation high-performing deep-UV NLO materials.

Multiple Functions of l-Thioproline in the Synthesis of Chiral Metal Bromides Showing Second-Harmonic-Generation Responses

Three new homochiral metal bromides, namely, (l-Htp)2Cu2Br4 (1), (l-Htp)(l-tp)CdBr3 (2), and (l-tp)2ZnBr2 (3), were prepared using l-thioproline as the chiral template. These compounds feature dimeric, chainlike, and monomeric structures. Their second-harmonic-generation (SHG) efficiencies are 0.1, 0.3, and 2.0 times that of KH2PO4, respectively. Density functional theory calculations were performed to reveal the origin of the SHG response of compound 3.

Cadmium Hydroxyl Chloride with Balanced Band Gap and Second-Harmonic-Generation Response

Ultraviolet (UV) nonlinear-optical (NLO) materials are crucial in laser technology due to their ability to modulate light frequency. In this work, when d10 cations, hydroxyl groups, and Cl atoms were combined, a cadmium double salt, Cd(OH)Cl, was synthesized by a simple hydrothermal method. It has a large phase-matched second-harmonic-generation (SHG) response at 1064 nm (2.5 × KDP) with a short UV-cutoff edge (260 nm), which can be applied in a solar-blind UV band. Theoretical calculations suggest that [Cd(OH)3Cl3] groups lead to a large SHG response. Our work may shed light on the exploration of new NLO materials in metal hydroxyl chlorides.

In Situ Chiral Template Approach to Synthesize Homochiral Lead Iodides for Second-Harmonic Generation

Homochiral halide perovskites have gained increasing attention because of their fascinating optoelectronic properties and prospective applications in laser technologies. However, the limited choice of chiral organic templates severely restricts their structural diversity and second-harmonic generation (SHG) effects. Here, we present an in situ chiral template approach for the synthesis of one-dimensional (1D) homochiral lead iodides. A chiral imine (L-ipp) template was generated in situ by reacting L-proline (L-pro) and acetone under ambient conditions. Notably, L-ipp can cooperate with L-pro to direct the formation of a homochiral lead iodide with dual chiral templates, which is unprecedented in crystalline metal halides. The homochiral lead iodide containing both L-ipp and L-pro shows a strong SHG response of 8.0 times that of KH2 PO4 (8.0×KDP). The SHG efficiency is one of the largest values reported to date for any homochiral lead halides under 1064 nm laser irradiation. A comparative study shows that homochiral 1D lead iodides containing either L-ipp or L-pro exhibit relatively weak SHG responses (≤1.0×KDP). This work demonstrates the advantage of using two different chiral templates over a single chiral template in enhancing the SHG responses of halide materials.

Free Halogen Substitution of Chiral Hybrid Metal Halides for Activating the Linear and Nonlinear Chiroptical Properties

Halogen substitution has been proven as an effective approach to the band gap engineering and optoelectronic modulation of organic-inorganic hybrid metal halide (OIHMH) materials. Various high-performance mixed halide OIHMH film materials have been primarily obtained through the substitution of coordinated halogens in their inorganic octahedra. Herein, we propose a new strategy of substitution of free halogen outside the inorganic octahedra for constructing mixed halide OIHMH single crystals with chiral structures, resulting in a boost of their linear and nonlinear chiroptical properties. The substitution from DMA4[InCl6]Cl (DMA = dimethylammonium) to DMA4[InCl6]Br crystals through a facile antisolvent vaporization method produces centimeter-scale single crystals with high thermal stability along with high quantum yield photoluminescence, conspicuous circularly polarized luminescence, and greatly enhanced second harmonic generation (SHG). In particular, the obtained DMA4[InCl6]Br single crystal features an intrinsic chiral structure, exhibiting a significant SHG circular dichroism (SHG-CD) response with a highest reported anisotropy factor (gSHG-CD) of 1.56 among chiral OIHMH materials. The enhancements in both linear and nonlinear chiroptical properties are directly attributed to the modulation of octahedral distortion. The mixed halide OIHMH single crystals obtained by free halogen substitution confine the introduced halogens within free halogen sites of the lattice, thereby ensuring the stability of compositions and properties. The successful employment of such a free halogen substitution approach may broaden the horizon of the regulation of structures and the optoelectronic properties of the OIHMH materials.

NaCl·CH4N2O·H2O: An Organic-Inorganic Hybrid Ultraviolet Nonlinear Optical Crystal with Optimized Comprehensive Properties

Ultraviolet (UV) nonlinear optical (NLO) crystals are a vital component in laser systems to modulate frequency. Organic groups have the advantages of easy synthesis, structural diversity, and large hyperpolarizations (β), which can be combined with inorganic groups to form unique organic-inorganic hybrid NLO crystal materials. Herein, a urea-containing crystal NaCl·CH4N2O·H2O is screened out and large-size crystals have been grown by a simple aqueous solution method. Compared with most reported organic-inorganic hybrid NLO materials, it has optimized comprehensive properties including a large SHG effect of 1.53 × KDP, a moderate birefringence (0.084@1064 nm), and a short UV cutoff edge of 209 nm. First-principles studies reveal that the dominant contributor to the linear and nonlinear optical properties is the urea molecule.

Two Carboxylate-Cyanurates with Strong Optical Anisotropy and Large Band Gaps

The first metal carboxylate-cyanurates, namely, K(H₃C₃N₃O₃)(HCO₂) (I) and Ba₂(H₂C₃N₃O₃)(CH₃CO₂)₃(H₂O) (II), which contain π-conjugated carboxylate and cyanurate groups, have been synthesized by hydrothermal methods. They crystallize in centrosymmetric space groups of P1̅ and P2₁/n, respectively. Compound I exhibits a novel three-dimensional (3D) structure based on a [K(H₃C₃N₃O₃)]⁺ cationic framework with 12-membered ring (12-MR) channels, and the (HCO₂)^- anions are located within the 12-MR channels. The [K(H₃C₃N₃O₃)]⁺ cationic framework is composed of K⁺ ions interconnected by H₃C₃N₃O₃ ligands. Compound II features a 3D network formed by [Ba₂(CH₃CO₂)₃]⁺ cationic double chains bridged by (H₂C₃N₃O₃)^- anions. The [Ba₂(CH₃CO₂)₃]⁺ cationic double chain is composed of (CH₃CO₂)^- anions and Ba²⁺ ions. Optical property measurements show that both compounds exhibit short ultraviolet cutoff edges (I, 208 nm; II, 218 nm) and wide band gaps (I, 5.43 eV; II, 5.20 eV). Importantly, K(H₃C₃N₃O₃)(HCO₂) (I) features a large birefringence of 0.285@532 nm due to the parallel alignment of π-conjugated H₃C₃N₃O₃ and (HCO₂)^- groups, indicating that K(H₃C₃N₃O₃)(HCO₂) (I) is a promising short-wave ultraviolet birefringent material. Detailed theoretical calculations elucidate that their excellent optical properties originate from the synergetic effect of both types of π-conjugated groups.

The Antiperovskite-Type Oxychalcogenides Ae3 Q[GeOQ3 ] (Ae = Ba, Sr; Q = S, Se) with Large Second Harmonic Generation Responses and Wide Band Gaps

Oxychalcogenides capable of exhibiting excellent balance among large second-harmonic generation (SHG) response, wide band gap (E_g ), and suitable birefringence (Δn) are ideal materials class for infrared nonlinear optical (IR NLO) crystals. However, rationally designing a new high-performance oxychalcogenide IR NLO crystal still faces a huge challenge because it requires the optimal orientations of the heteroanionic groups in oxychalcogenide. Herein, a series of antiperovskite-type oxychalcogenides, Ae₃ Q[GeOQ₃ ] (Ae = Ba, Sr; Q = S, Se), which were synthesized by employing the antiperovskite-type Ba₃ S[GeS₄ ] as the structure template. Their structures feature novel three-dimensinoal frameworks constructed by distorted [QAe₆ ] octahedra, which are further filled by [GeOQ₃ ] tetrahedra to form antiperovskite-type structures. Based on the unique antiperovskite-type structures, the favorable alignment of the polarizable [GeOQ₃ ] tetrahedra and distorted [QAe₆ ] octahedra have been achieved. These contribute the ideal combination of large SHG response (0.7-1.5 times that of AgGaS₂ ), wide E_g (3.52-4.10 eV), and appropriate Δn (0.017-0.035) in Ae₃ Q[GeOQ₃ ]. Theoretical calculations and crystal structure analyses revealed that the strong SHG and wide E_g could be attributed to the polarizable [GeOQ₃ ] tetrahedra and distorted [QAe₆ ] octahedra. This research provides a new exemplification for the design of high-performance IR NLO materials.

Dual-Ligand-Oriented Design of Noncentrosymmetric Complexes with Nonlinear-Optical Activity

When the N- and O-donor ligands are combined as coligands, two noncentrosymmetric (NCS) complexes of [Ni(p-bdc)(tipa)(H₂O)₂]₂·H₂O (1) and Ni(npdc)(tipa)H₂O (2) [tipa = tris[4-(1H-imidazol-1-yl)phenyl]amine, p-H₂bdc = 1,4-benzenedicarboxylic acid, and H₂npdc = 2,6-naphthalenedicarboxylic acid] were achieved under solvothermal conditions. For both structures, N-donor ligands are responsible for the generation of a layered structure, while the O-donor ligands are hung on the layers and are responsible for enhancing the polarity, giving rise to the NCS structures. Because of the different connection modes between the metal centers and different carboxylate ligands (p-bdc^2- in 1 and npdc^2- in 2), 1 and 2 show some structural differences. The p-bdc^2- ligands in 1 are suspended on the upper and lower sides of the [Ni(tipa)]_n layers, while all of the npdc^2- ligands in 2 hang on one side of the [Ni(tipa)]_n layers and point in the same direction, which makes the two NCS complexes show phase-matchable behavior with different second-harmonic-generation (SHG) responses of about 0.9 and 1.5 times that of KH₂PO₄ (KDP), respectively. Theoretical studies reveal that charge transfers between Ni²⁺ and carboxylate ligands make the dominant contribution to the optical properties. It is expected that a dual-ligand strategy may guide the design of novel superior-performing NCS complexes.

Metal oxyhalides: an emerging family of nonlinear optical materials

Second-order nonlinear optical (NLO) materials have drawn enormous academic and technological attention attributable to their indispensable role in laser frequency conversion and other greatly facilitated applications. The exploration of new NLO materials with high performances thus has long been an intriguing research field for chemists and material scientists. However, an ideal NLO material should simultaneously satisfy quite a few fundamental yet rigorous criteria including a noncentrosymmetric structure, large NLO coefficients, desired transparent range, large birefringence, high laser damage threshold, and availability of a large-size single crystal. Therefore, the identification of promising compound systems, targeted design, and experience-based syntheses are crucial to discover novel NLO materials working in the spectral region of interest. As an important family of mixed-anion compounds, versatile metal oxyhalides containing metal-centered oxyhalide functional units ([MO m X n ] (X = F, Cl, Br, and I)) are becoming a marvelous branch for interesting NLO materials. Especially, when the central metals are d0/d10 transition metals or heavy post-transition metals, a number of novel NLO materials with superior functionalities are expected. Our thorough review on the recent achievements of metal oxyhalides for NLO materials are divided into the fast-growing NLO metal oxyhalides with single type halogen anions and the newly identified NLO metal oxyhalides with mixed halogen anions. Here we mainly focus on the design strategy, structural chemistry, NLO-related properties, and structure-property correlation of the metal oxyhalides with relatively large NLO responses. We hope this review can provide an insight on the rational design and future development of emerging metal oxyhalides for NLO and other applications.

HgTeO2F(OH): A Nonlinear Optical Oxyfluoride Constructed of Active [TeO2F(OH)]2- Pyramids and V-Shaped [HgO2]2- Groups

Oxyhalides possessing the merits of oxides and halides have widely received attention for their comprehensive physical performances, especially as potential nonlinear optical (NLO) crystals. Here, based on conventional strategy for obtaining acentric compounds, a Te⁴⁺ lone-pair cation was introduced into oxyhalides, and one oxyfluoride, HgTeO₂F(OH), was obtained via a hydrothermal reaction. Crystallized in the polar space group Pca2₁, the layered structure of HgTeO₂F(OH) is composed of V-shaped [HgO₂]^2- groups and [TeO₂F(OH)]^2- pyramids, in which the [TeO₂F(OH)]^2- pyramid first served as the NLO functional motif. Its powder sample exhibits a phase-matchable SHG response of 1.1 × KH₂PO₄ at 1064 nm, and its birefringence (0.09@1064 nm) is sufficient for phase-matchable behavior, which manifests its comprehensive capacity as a promising NLO candidate. Theoretical calculations about electronic structure and optical properties are also carried out, revealing that the Te⁴⁺ lone-pair cation makes the predominant contribution to the SHG effect and synergizes with the [HgO₂]^2- groups.

Performance of optical materials with derivative planar π-conjugated groups: Recent advances and future prospects

Planar π-conjugated groups which possess not only large hyperpolarizability but also optical anisotropy are proven to be a good functional motif for optical materials with outstanding nonlinear optics and/or birefringence....

APb2(C7H3NO4)2I (A = K, Rb, Cs): rare stable nonlinear optical crystals with second-harmonic generation response and highly distorted lead core coordination polyhedra

APb2(C7H3NO4)2I (A = K, Rb, Cs) features a 3D NCS cubic framework consisting of highly distorted [PbNO5] and [PbNO4I] coordination polyhedra, a moderate SHG response, a wide transparent window and a high thermal stability above 300 °C.

An excellent lead oxyiodide with a strong second-harmonic generation response and a large birefringence induced by the oriented arrangement of highly distorted [PbO4I2] polyhedra

K2I[PbI(OOCCH2COO)] featuring the strongest second-harmonic generation response among malonates, a large birefringence, a wide transparent window and good stability is induced by the oriented arrangement of highly distorted bifunctional [PbO4I2] polyhedra.

KCs2Pb2(HCOO)2Cl5: A Lead Formate with Strong Second-Harmonic-Generation Response Obtained by an Anionic Substitution

Nonlinear optical (NLO) materials are playing an increasingly vital role in laser science and technology. Herein, we report a new lead formate, KCs₂Pb₂(HCOO)₂Cl₅, successfully synthesized by using mild mix-solvothermal methods. By the anionic substitution of a [CH₃COO] group with a [HCOO] group, the dipole moment of the distorted [PbCl₄O₂] polyhedron is increased. In contrast, polarization from the anionic group and the volume of the unit cell are reduced. Hence, KCs₂Pb₂(HCOO)₂Cl₅ possesses a strong second-harmonic-generation (SHG) response of 4.2 times that of KH₂PO₄ (KDP), a transparent window covering 0.43-1.87 μm, a large band gap of 3.52 eV, and moderate birefringence (0.11@1064 nm). Systematic theoretical calculations illustrate the origin of the linear and nonlinear optical properties of KCs₂Pb₂(HCOO)₂Cl₅. This research provides a viable strategy for the design and synthesis of new NLO crystals.

A Lead Mixed Halide with Three Different Coordinated Anions and Strong Second-Harmonic Generation Response

Nonlinear optical (NLO) crystals are widely applied in information technology, micro-manufacturing and medical treatment. Herein, a new lead mixed halide with strong second-harmonic generation (SHG) response, Cs₃ Pb₂ (CH₃ COO)₂ Br₃ I₂ , has been designed and rationally synthesized. Cs₃ Pb₂ (CH₃ COO)₂ Br₃ I₂ represents the rare NLO crystal featuring that three different anions (I^- , Br^- and O^2- ) simultaneously coordinate the Pb(II) atom to form a severely distorted [PbBr₂ I₂ O₂ ] polyhedron with a large polarizability. Remarkably, Cs₃ Pb₂ (CH₃ COO)₂ Br₃ I₂ not only exhibits a very strong phase-matching SHG response of 9×KH₂ PO₄ (KDP), but also possesses a large birefringence (0.27@1064 nm) and high laser damage threshold (LDT). The strong SHG effect of Cs₃ Pb₂ (CH₃ COO)₂ Br₃ I₂ mainly originates from the oriented arrangement of [Pb₂ Br₃ I₂ ] chains. This study points out an effective strategy to develop new NLO crystals with strong SHG response.

Hydrogen-Bond-Driven Synergistically Enhanced Hyperpolarizability: Chiral Coordination Polymers with Nonpolar Structures Exhibiting Unusually Strong Second-Harmonic Generation

Four chiral coordination polymers (CPs), M[(S,S)-C₁₄ H₁₄ N₂ O₆ ] and M[(R,R)-C₁₄ H₁₄ N₂ O₆ ] (M=Zn or Cd), have been exclusively synthesized in high yields with the aid of newly designed chiral ligand under hydrothermal condition. The CPs crystallizing in the orthorhombic nonpolar space group, C222₁ , reveal three-dimensional framework structures composed of MO₄ tetrahedra and the corresponding homochiral linkers. Powder second-harmonic generation (SHG) measurements indicate that the nonpolar CPs reveal very strong SHG efficiency of ca. 5-9 times that of KH₂ PO₄ and exhibit type-I phase-matching behavior. Density functional theory calculations suggest that the unusually large SHG efficiency found from the nonpolar CPs should be attributable to the synergistic effect of polarizable metal cations and enhanced hyperpolarizability in the donor-acceptor system originating from the hydrogen bonding in the coordinated linkers.

KCs2 [Pb2 Br5 (HCOO)2 ]: A Polar 3D Lead-Bromide Framework Exhibiting Strong Second-Harmonic Generation Response

The discovery of new nonlinear optical (NLO) crystals with excellent properties is in urgently demand because of their ability to generate coherent light. Herein, we report an unique NLO lead bromide formate, KCs₂ [Pb₂ Br₅ (HCOO)₂ ], which has been synthesized by a mix-solvothermal method. KCs₂ [Pb₂ Br₅ (HCOO)₂ ] exhibits strong phase-matching second-harmonic generation (SHG) response (6.5×KDP), large birefringence (0.16@ 1064 nm), and a wide transparent window in most visible light and mid-IR region. Interestingly, KCs₂ [Pb₂ Br₅ (HCOO)₂ ] features a polar 3D lead-bromide framework in which adjacent Pb-Br layers containing coplanar Pb₆ Br₆ rings are not only parallel to each other, but also orient in the same direction. These oriented arrangements are responsible for the strong SHG response and large birefringence that are elucidated by both local dipole moment and theoretical calculations. This research provides a new strategy to explore subsequent NLO crystals.

Be2 (BO3 )(IO3 ): The First Anion-mixed Van der Waals Member in the KBe2 BO3 F2 Family with a Very Strong Second Harmonic Generation Response

To obtain new nonlinear optical (NLO) materials with a large second harmonic generation (SHG) effect has always been a great challenge. We have synthesized the first metal borate-iodate NLO crystal, Be₂ (BO₃ )(IO₃ ) (BBIO), by multicomponent modification of KBe₂ BO₃ F₂ (KBBF), in which the structural features of KBBF were maintained and (IO₃ )^- groups were connected to honeycomb [Be₂ BO₃ O₂ ]_∞ layers. As the first KBBF family member with mixed anionic groups, BBIO benefited from the synergistic effect of (IO₃ )^- , (BO₃ )^3- and (BeO₄ )^6- groups, and exhibited a very strong SHG response of ≈7.2×KH₂ PO₄ (KDP, @1064 nm) and a large birefringence (Δn) of 0.172 at 1064 nm. BBIO may, unexpectedly, optimize growth habits via van der Waals forces. This study presents borate-iodate as a new NLO material and it demonstrates opportunities in KBBF structural engineering.

Titanium Iodates with a Second-Harmonic-Generation Response

Nonlinear-optical (NLO) crystal is an important photoelectric functional material. In this work, a new NLO titanium iodate, (H₃O)₂Ti(IO₃)₆, along with Ti(IO₃)₄ has been synthesized under facile conditions. The space group of (H₃O)₂Ti(IO₃)₆ is the chiral noncentrosymmetric group R3 (No. 146), with an interesting three-dimensional framework, while that of Ti(IO₃)₄ is the centrosymmetric space group P1̅ (No. 2) containing one-dimensional chains. Thermogravimetric analysis shows that (H₃O)₂Ti(IO₃)₆ and Ti(IO₃)₄ have no weight loss below 220 and 390 °C, respectively. In addition, (H₃O)₂Ti(IO₃)₆ not only is thermally stable up to 200 °C in an air atmosphere but also is stable in water. (H₃O)₂Ti(IO₃)₆ has a moderate-intensity second-harmonic-generation (SHG) response (1.4×KDP), a large laser-induced damage threshold (46×AgGaS₂), and high transmittance in the wavelength ranges of 0.5-1.4 and 2.5-10 μm. Both local dipole moment and systematic theoretical calculations reveal that the SHG response of (H₃O)₂Ti(IO₃)₆ is mainly because of the combined effect of [TiO₆] octahedra and IO₃ and IO₄ units. In a word, (H₃O)₂Ti(IO₃)₆ exhibits good NLO performances, as well as water resistance and facile growth of a single crystal with high quality, indicating its potential application as NLO materials in the visible and mid-IR regions, especially the visible region.

Two Lead Halides with Strong SHG Response Obtained by the Isovalent Substitutions of Alkali Metal Cation and Halogen Anion

The substitution of alkali metal cation or halogen anion based on nonlinear crystals is an effective strategy to exploit new optical materials. The strategy has been successfully expanded to discover two new lead halides, Rb₃Pb₂(CH₃COO)₂X₅ (X = Br, Cl). The substitution of the Cs⁺ cation with a Rb⁺ cation can not only increase the local dipole moment of the distorted [PbBr₄O₂] polyhedron but also reduce the cell unit, resulting in a large net macroscopic polarization. Therefore, Rb₃Pb₂(CH₃COO)₂Br₅ possesses a strong second-harmonic generation (SHG) response (6 × KDP) and a large birefringence (0.18@1064 nm). Furthermore, by the substitution of the Br^- anion with a Cl^- anion, Rb₃Pb₂(CH₃COO)₂Cl₅ exhibits a high laser damage threshold (LDT, 84 × AgGaS₂) and a short UV cutoff edge of 287 nm, as well as moderate SHG response (3 × KDP) and birefringence (0.11@1064 nm). Detailed theory calculations elucidate the origin of the linear and nonlinear optical properties of these compounds.