一种同时具备显著增强的双折射和二次谐波效应的类BBO三聚硫氰酸盐

在新兴的自旋轨道角动量光子技术领域,对兼具强二次谐波和大双折射的非线性光学晶体有很大的需求.基于此,本文采用具有大π共轭效应的[HC_(3)N_(3)S_(3)]_(2)−和碱金属阳离子K+相结合,成功合成了一例新型类β-BaB_(2)O_(4)(BBO)手性三聚硫氰酸盐K_(4)(HC_(3)N_(3)S_(3))_(2)·H_(2)O(1).与具有最优排列的π共轭[B3O6]3−环的BBO相比,1中[HC_(3)N_(3)S_(3)]_(2)−环的排列并不理想,但倍频响应和双折射显著增强(1.8×BBO;Δn=0.402@550 nm,~3.3×BBO).第一性原理计算分析表明,π共轭[HC_(3)N_(3)S_(3)]_(2)−环是产生优异光学性能的根本原因.这项工作证明了π共轭[HC_(3)N_(3)S_(3)]_(2)−是优秀的双功能“材料基因”,在新兴光子技术的光学集成器件研究中值得更多的关注.

Maximizing the linear and nonlinear optical responses of alkaline tricyanomelaminate

High-performance bi-functional materials are in urgent demand for the next-generation integrated optical devices.In this work,we successfully synthesized the first tricyanomelaminate with bi-functional optical responses,namely Cs_(3)C_(6)N_(9)•H_(2)O(I),from its analogue Na_(3)C_(6)N_(9)•3H_(2)O by a facile ion exchange method.In contrast to Na_(3)C_(6)N_(9)•3H_(2)O,I realizes an optimal arrangement of𝜋π-conjugated(C_(6)N_(9))3−anion groups in its crystal structure.As a result,the second-order nonlinear optical(NLO)response is greatly enhanced from nearly zero of Na_(3)C_(6)N_(9)•3H_(2)O to∼9.8×KH_(2)PO_(4)of I.Furthermore,I exhibits a giant linear optical anisotropic response(i.e.birefringence)of 0.52 at the wavelength of 550 nm.Both responses are almost the largest among the inorganic compounds ofπ-conjugated rings,which indicates that I has great potential as a bi-functional optical crystal.Structural and theoretical analyses reveal the microscopic origin of excellent optical properties.This work would attract a lot of interest to the persistently neglected potential of tricyanomelaminates as linear optical and NLO crystals.

Recent advances in non-π-conjugated nonlinear optical sulfates with deep-UV absorption edge

Deep-ultraviolet(deep-UV)nonlinear optical(NLO)crystals are of current interest because they play an indis-pensable role in modern scientific equipment.Searching these crystals was traditionally limited toπ-conjugated systems,such as borates and carbonates.In 2019,our group reported two non-π-conjugated sulfates as new sources of deep-UV NLO crystals for the first time.In this mini review,we provide a comprehensive overview of the recent development of non-π-conjugated NLO sulfates with deep-UV absorption edge in aspect of synthesis methods,crystal structures,thermal stability,and optical performance.Besides,we conclude the crucial structure-property relationships,and further give some prospects for exploring non-π-conjugated NLO sulfates with deep-UV absorption edge with high thermal stability,enhanced second-order NLO effects,birefringence,etc.We believe that this mini review will not only facilitate researchers to design superior non-π-conjugated NLO sulfates with deep-UV absorption edge but also shed useful insights on the explorations of other non-π-conjugated deep-UV NLO crystal systems.

Accurate design and synthesis of nonlinear optical crystals employing KBe_(2)BO_(3)F_(2) as structural template

In spite of decades of great efforts,it is still very challenging to realize accurate design and synthesis of second-order nonlinear optical(NLO)crystals.KBe_(2)BO_(3)F_(2)(KBBF)is the sole NLO material that can output deep-ultraviolet light by direct second-harmonic generation process,so it is an ideal choice to use KBBF as the structural template to design environment-friendly candidates with better growth habit based on the reported compounds.In this review,we will elaborate the accurate design and synthesis of high-performance NLO ma-terials from the perspective of microscopic crystal structure based on KBBF,hoping to provide deep understanding on how to rationally design and synthesize targeted compounds efficiently and quickly.In addition,according to multiple requirements on ultraviolet NLO crystals,including second-harmonic generation,cut-off edge,and birefringence,we propose a new concept so-called quality factor to comprehensively evaluate the overall per-formance of new ultraviolet NLO materials.This concept would help to directly and readily evaluate the ability of an ultraviolet NLO material to achieve practical NLO output.

Preface to Nonlinear Optical Crystals

Nonlinear optical(NLO)crystals are core materials in laser frequency-conversion technique,and the requirement on the laser wavelength varies from one application to another.Now,the commercial NLO crystals,e.g.,KDP,LBO,BBO,KTP,AgGaS_(2),ZnGeP_(2),et al.,have prevailed in ultraviolet(UV)/visible and near-/mid-infrared region for decades.

Preface to Nonlinear Optical Crystals

Nonlinear optical(NLO)crystals can efficiently convert the frequency of common solid-state laser with fixed or limited wavelengths.Since the first observation of second-harmonic generation(SHG)phenomenon in the early 1960s,they have played an increasing role in the fields of laser spectra,precision measurements,and quantum information,as well as industrial laser processing,and so on.However,it is still challenging to rationally design and synthesize new NLO crystals.

A new 2D van der Waals material with air stability and in-plane anisotropy

1.Text 2D van der Waals materials possess intriguing features[1],especially optically,such as high nonlinear optical responses[2],broadband spectral response[3],and accessible exciton effects[4].Unlike conventional 2D materials with in-plane isotropy,such as graphene and M0S_(2),2D van der Waals materials with in-plane anisotropic possess in-plane low symmetry structure,inducing the in-plane anisotropic physical properties.Meanwhile,they can be easily moved to various substrates without lattice-matching problems.

Nonpolar Na_(10)Cd(NO_(3))_(4)(SO_(3)S)_(4) Exhibits a Large Second-Harmonic Generation

Conventional wisdom says that nonpolar structures do not favorably produce strong second-harmonic generation(SHG)responses since the polarization in their microscopic functional groups are counteracted.Herein,we report the first nonlinear optical thiosulfate,Na_(10)Cd(NO_(3))_(4)(SO_(3)S)_(4),which crystallizes in a nonpolar space group of P−4.However,this thiosulfate exhibits a strong SHG response of about 4.2 times that of the benchmark KH2PO4,which is larger than those of polar sulfates.According to first-principles calculations and a flexible dipole model,the SHG enhancement is mainly ascribed to the larger flexibility of the S=S bond in the SO_(3)S tetrahedra in comparison with the S–O bond in the SO4 tetrahedra.These findings indicate that constructing flexible bonds is an effective strategy to design highperformance nonlinear optical materials regardless of polarity.

A Nonlinear Optical Switchable Sulfate of Ultrawide Bandgap

Nonlinear optical(NLO)switchable materials have attracted intense attention because of their promising applications in optoelectronic devices.However,previous studies are mainly limited to molecular-based compounds that usually exhibit narrow bandgaps.Here,we report all-inorganic Li_(9)Na_(3)Rb_(2)(SO_(4))_(7) as an ultrawide-bandgap NLO switchable material.

Designing a deep-UV nonlinear optical monofluorophosphate

As structural variants of famous hexagonal tungsten bronzes,hexagonal tungsten oxides(HTO)represent an important family with fascinating functional properties,such as piezoelectric,ferroelectric,pyroelectric,and nonlinear optical(NLO)properties.However,none of them are transparent in the deep-UV spectral region,which limits their applications.Herein,we report the first HTO-type monofluorophosphate K_(3)Sc_(3)(PO_(4))(PO_(3)F)_(2)F_(5)(I)with deep-UV transparency.Such a monofluorophosphate is NLO-active with a phase-matchable powder second harmonic generation efficiency of 0.9 times that of KH_(2)PO_(4)at 1,064 nm.Importantly,the UV-Vis reflectance spectrum indicates that it is deep-UV transparent down to 200 nm.This work pushes the transparent window of NLO materials with HTO-type structures down to the deep-UV spectral region for the first time and opens up a new door for HTO materials.

Noncentrosymmetric K_(2)Mn_(3)(SO_(4))_(3)F_(2)·4H_(2)O and Rb_(2)Mn_(3)(SO_(4))_(3)F_(2)·2H_(2)O with pseudo-KTP structures

Two fluoride sulfates,K_(2)Mn_(3)(SO_(4))_(3)F_(2)·4H_(2)O(Ⅰ) and Rb_(2)Mn_(3)(SO_(4))_(3)F_(2)·2H_(2)O (Ⅱ) are obtained by water solution method.Single-crystal X-ray diffraction analysis indicated that they crystallize in space groups of Cmc2_(1.)Their structures feature a pseudo-KTP structure consisting of interconnecting[Mn_(3)(SO_(4))3F_(2)(H_(2)O)2]_(∞) layers,which are further packing along the a axis with alkali metal cations balancing the charges.The structure relationships between the two compounds are discussed.Secondharmonic generation measurements manifest that Ⅰ and Ⅱ have similar second-harmonic generation responses of about 0.2 and 0.25 times that of KH_(2)PO_(4).