Beryllium-Free KBBF Family of Nonlinear-Optical Crystals: AZn₂BO₃X₂ (A = Na, K, Rb; X = Cl, Br)

A series of a novel beryllium-free KBBF family of nonlinear-optical materials AZn₂BO₃X₂ (A = K, Rb and X = Cl; A = Na, K, Rb and X = Br) were successfully synthesized through molecular engineering design, and single crystals of AZn₂BO₃Cl₂ (A = K, Rb) were grown by a spontaneous nucleation technique from self-flux systems. As a representative for the halogen KBBF family of crystals, KZn₂BO₃Cl₂ features the infinite lattice layer [Zn₂BO₃Cl₂]_∞ made up of BO₃ and ZnO₃Cl anionic groups, and the in-layer BO₃ groups are completely coplanar and well-aligned. Besides, KZn₂BO₃Cl₂ exhibits high transmittance in the range of 300–2000 nm with a UV-transmission cutoff of around 200 nm according to transmission spectra. The compounds of AZn₂BO₃Cl₂ (A = K, Rb) are both phase-matchable with powder second-harmonic-generation efficiencies of 1.3 and 1.17 times that of KH₂PO₄ for KZn₂BO₃Cl₂ and RbZn₂BO₃Cl₂, respectively, which are similar to that of KBBF

Beryllium-Free KBBF Family of Nonlinear-Optical Crystals: AZn₂BO₃X₂ (A = Na, K, Rb; X = Cl, Br)

A series of a novel beryllium-free KBBF family of nonlinear-optical materials AZn₂BO₃X₂ (A = K, Rb and X = Cl; A = Na, K, Rb and X = Br) were successfully synthesized through molecular engineering design, and single crystals of AZn₂BO₃Cl₂ (A = K, Rb) were grown by a spontaneous nucleation technique from self-flux systems. As a representative for the halogen KBBF family of crystals, KZn₂BO₃Cl₂ features the infinite lattice layer [Zn₂BO₃Cl₂]_∞ made up of BO₃ and ZnO₃Cl anionic groups, and the in-layer BO₃ groups are completely coplanar and well-aligned. Besides, KZn₂BO₃Cl₂ exhibits high transmittance in the range of 300–2000 nm with a UV-transmission cutoff of around 200 nm according to transmission spectra. The compounds of AZn₂BO₃Cl₂ (A = K, Rb) are both phase-matchable with powder second-harmonic-generation efficiencies of 1.3 and 1.17 times that of KH₂PO₄ for KZn₂BO₃Cl₂ and RbZn₂BO₃Cl₂, respectively, which are similar to that of KBBF

Deep-Ultraviolet Nonlinear Optical Materials: Na₂Be₄B₄O₁₁ and LiNa₅Be₁₂B₁₂O₃₃

Deep-UV coherent light generated by nonlinear optical (NLO) materials possesses highly important applications in photonic technologies. Beryllium borates comprising anionic planar layers have been shown to be the most promising deep UV NLO materials. Here, two novel NLO beryllium borates Na₂Be₄B₄O₁₁ and LiNa₅Be₁₂B₁₂O₃₃ have been developed through cationic structural engineering. The most closely arranged [Be₂BO₅]_∞ planar layers, connected by the flexible [B₂O₅] groups, have been found in their structures. This structural regulation strategy successfully resulted in the largest second harmonic generation (SHG) effects in the layered beryllium borates, which is ∼1.3 and 1.4 times that of KDP for Na₂Be₄B₄O₁₁ and LiNa₅Be₁₂B₁₂O₃₃, respectively. The deep-UV optical transmittance spectra based on single crystals indicated their short-wavelength cut-offs are down to ∼170 nm. These results demonstrated that Na₂Be₄B₄O₁₁ and LiNa₅Be₁₂B₁₂O₃₃ possess very promising application as deep-UV NLO crystals

Ca₃Na₄LiBe₄B₁₀O₂₄F: A New Beryllium Borate with a Unique Beryl Borate _∞²[Be₈B₁₆O₄₀F₂] Layer Intrabridged by [B₁₂O₂₄] Groups

A novel beryllium borate, Ca₃Na₄LiBe₄B₁₀O₂₄F, has been discovered. It possesses a unique _∞²[Be₈B₁₆O₄₀F₂] layer composed of two opposite parallel [Be₄B₄O₁₂F]_∞ layers bridged with [B₁₂O₂₄] polyborates. The linkage of [B₁₂O₂₄] to other structural units is first found in anhydrous borates. In the _∞²[Be₈B₁₆O₄₀F₂] layer, multiple tunnels are arranged along different directions resided by the alkali and alkaline-earth cations. The compound remains stable in an ambient atmosphere from room temperature to the melting point at 830 °C and melts incongruently

Metal Thiophosphates with Good Mid-infrared Nonlinear Optical Performances: A First-Principles Prediction and Analysis

The family of metal thiophosphates is an important but long-ignored compound system of the nonlinear optical (NLO) materials with desirable properties for the mid-infrared (mid-IR) coherent light generation. In the present work, the mid-IR NLO capabilities of metal thiophosphate crystals are systematically investigated based on their structure–property relationship. The linear and nonlinear optical properties of these crystals are predicted and analyzed using the first-principles calculations. In particular, several metal thiophosphate compounds are highlighted to exhibit good mid-IR NLO performances, as supported by the primary experimental results. These candidates would greatly promote the development of the mid-IR NLO functional materials

Midinfrared Nonlinear Optical Thiophosphates from LiZnPS₄ to AgZnPS₄: A Combined Experimental and Theoretical Study

Our earlier theoretical calculation and preliminary experiment highlighted LiZnPS₄ as a good mid-infrared (mid-IR) nonlinear optical (NLO) material. However, this compound suffers from problems including corrosion of the silica tubes, a pungent smell, deliquescence, and incongruent-melting behavior in the further single crystal growth and applications. In order to overcome these problems, herein, we investigate the analogues of LiZnPS₄ and propose that AgZnPS₄ would be a good candidate. The combination of experimental and theoretical study demonstrates that AgZnPS₄ exhibits a much stronger NLO effect than that of LiZnPS₄ despite the relatively smaller energy band gap. More importantly, AgZnPS₄ melts congruently with a melting point as low as 534 °C, much lower than those of traditional IR NLO crystals, and is nondeliquescent with enough stability in the air. Such a good crystal growth habit and chemical stability enable AgZnPS₄ to possess much better overall performance for the practical mid-IR NLO applications

Ca₃Na₄LiBe₄B₁₀O₂₄F: A New Beryllium Borate with a Unique Beryl Borate _∞²[Be₈B₁₆O₄₀F₂] Layer Intrabridged by [B₁₂O₂₄] Groups

A novel beryllium borate, Ca₃Na₄LiBe₄B₁₀O₂₄F, has been discovered. It possesses a unique _∞²[Be₈B₁₆O₄₀F₂] layer composed of two opposite parallel [Be₄B₄O₁₂F]_∞ layers bridged with [B₁₂O₂₄] polyborates. The linkage of [B₁₂O₂₄] to other structural units is first found in anhydrous borates. In the _∞²[Be₈B₁₆O₄₀F₂] layer, multiple tunnels are arranged along different directions resided by the alkali and alkaline-earth cations. The compound remains stable in an ambient atmosphere from room temperature to the melting point at 830 °C and melts incongruently

Deep-Ultraviolet Nonlinear Optical Materials: Na₂Be₄B₄O₁₁ and LiNa₅Be₁₂B₁₂O₃₃

Deep-UV coherent light generated by nonlinear optical (NLO) materials possesses highly important applications in photonic technologies. Beryllium borates comprising anionic planar layers have been shown to be the most promising deep UV NLO materials. Here, two novel NLO beryllium borates Na₂Be₄B₄O₁₁ and LiNa₅Be₁₂B₁₂O₃₃ have been developed through cationic structural engineering. The most closely arranged [Be₂BO₅]_∞ planar layers, connected by the flexible [B₂O₅] groups, have been found in their structures. This structural regulation strategy successfully resulted in the largest second harmonic generation (SHG) effects in the layered beryllium borates, which is ∼1.3 and 1.4 times that of KDP for Na₂Be₄B₄O₁₁ and LiNa₅Be₁₂B₁₂O₃₃, respectively. The deep-UV optical transmittance spectra based on single crystals indicated their short-wavelength cut-offs are down to ∼170 nm. These results demonstrated that Na₂Be₄B₄O₁₁ and LiNa₅Be₁₂B₁₂O₃₃ possess very promising application as deep-UV NLO crystals

Nonbonding Electrons Driven Strong SHG Effect in Hg₂GeSe₄: Experimental and Theoretical Investigations

A Hg-based ternary infrared nonlinear optical (NLO) material, Hg₂GeSe₄, with the defect diamond-like (DL) structure was systematically investigated for the first time. The experimental results show that Hg₂GeSe₄ exhibits an enhanced second harmonic generation (SHG) response about 2.1 times that of the normal DL selenide AgGaSe₂ (<i>d</i>₃₆ = 33 pm/V) at the particle size of 150–200 μm, as well as good phase-matchable ability. Moreover, theoretical analysis reveals that the nonbonding electrons around Se atoms in the defect DL structure make a dominant contribution to the improvement of the NLO property: <i>d</i>₃₆ = 78.83 pm/V and Δ<i>n</i> = 0.11. This study highlights the promise of electronic engineering strategies and opens new avenues toward the design of new infrared NLO crystals with high performance

Prospects for Fluoride Carbonate Nonlinear Optical Crystals in the UV and Deep-UV Regions

Combined with first-principles simulations and materials design considerations, the prospects of fluoride carbonate nonlinear optical (NLO) crystals in the ultraviolet (UV) and deep-UV regions are investigated. The <i>A</i>_<i>l</i>(CO₃)_<i>k</i>­F_<i>m</i>-type (<i>A</i> represents the alkaline and/or alkaline-earth metal elements) carbonates are focused since they have exhibited the potential for the UV harmonic generation. The recently discovered <i>MN</i>­CO₃F (<i>M</i> = K, Rb, Cs; <i>N</i> = Ca, Sr, Ba) series are selected as the representative examples to study the linear and nonlinear properties. It is revealed that <i>MN</i>­CO₃F possess very large birefringence and a strong NLO effect; thus, they are suitable to be good NLO and birefringent crystals in the UV region. Nevertheless, these carbonates cannot be applied in the deep-UV region because of their relatively small energy band gaps. To overcome this problem, we propose that the appropriate choice of the cations <i>A</i> would effectively enlarge the band gaps, which will greatly extend the applications of fluoride carbonates into the deep-UV region