Toward Large Second-Harmonic Generation and Deep-UV Transparency in Strongly Electropositive Transition Metal Sulfates.

The development of deep-ultraviolet (DUV)/solar-blind UV nonlinear optical (NLO) crystals simultaneously possessing wide UV transparency, strong second-harmonic generation (SHG) response, and suitable birefringence is a major challenge in advanced laser technology. We herein propose a "cation compensation" strategy for strong optical nonlinearity in inorganic solids that is exemplified by the introduction of strongly electropositive transition metals (TMs). Following this strategy, the first d0 TM UV-transparent NLO sulfates, MF2(SO4) (M = Zr (ZFSO), Hf (HFSO)), have been synthesized. Short UV cutoff edges of 206 nm and below 190 nm are observed for bulk ZFSO and HFSO crystals, respectively, together with the strongest powder SHG responses (3.2 × (ZFSO) and 2.5 × KDP (HFSO)) for solar-blind UV/DUV NLO sulfates, as well as suitable birefringence. This work provides a new and efficient approach to the development of urgently needed high-performance NLO materials for applications in the short-wavelength UV region.

A Sharp Improvement of Sulfate's Birefringence Induced by the Synergistic Effect of Heteroleptic and Dimeric Strategies.

As for tetrahedron-based ultraviolet nonlinear optical crystals, it is so difficult to achieve a sufficient birefringence to satisfy the phase-matching condition. Thereover, it is necessary to greatly increase the polarizability anisotropy of tetrahedra. Meanwhile, the tetrahedra should be arranged as uniformly as possible. Based on these ideas, a new strategy that dimerizes the heteroleptic tetrahedra with heteroleptic atoms as bridges is proposed and implemented, resulting in a new compound, Na2 S3 O6 , which crystallizes in a centrosymmetric monoclinic phase (phase-I) and a non-centrosymmetric orthorhombic one (phase-II). In the phase-I, a large birefringence of 0.103 @ 546 nm comparable to those of many triangle-based crystals is confirmed experimentally, indicating the ability of [S3 O6 ] group in improving the birefringence. Besides, the phase-II exhibits an improved birefringence of 0.056 @ 546 nm and a moderate second harmonic generation response of 1.4 × KH2 PO4 . In particular, the phase-II exhibits a typical phase-matching behavior under the irradiation of 532 nm laser. Moreover, the excellent optical properties of [S3 O6 ] group are further verified by theoretical calculations. These results completely illustrate the validity of the design strategy. Therefore, this work lights a new route for exploring novel ultraviolet nonlinear optical crystals.

Giant Second-Harmonic Generation Response and Large Band Gap in the Partially Fluorinated Mid-Infrared Oxide RbTeMo2O8F.

Strong second-harmonic generation (SHG) and a wide band gap are two crucial but often conflicting parameters that must be optimized for practical nonlinear optical (NLO) materials. We report herein the first d0-transition-metal (TM) tellurite with half of the d0-TM-octahedra partially fluorinated, namely, quinary RbTeMo2O8F, which exhibits giant SHG responses (27 times that of KH2PO4 (KDP) and 2.2 times that of KTiOPO4 (KTP) with 1064 and 2100 nm laser radiation, respectively), the largest SHG values among all reported metal tellurites. RbTeMo2O8F also possesses a large band gap (3.63 eV), a wide optical transparency window (0.34-5.40 µm), and a significant birefringence (Δn = 0.263 at 546 nm). Theoretical calculations and crystal structure analysis demonstrate that the outstanding SHG responses can be definitively attributed to the uniform alignment of the polarized [MoO5F]/[MoO6] octahedra and the seesaw-like [TeO4], and the consequent favorable summative polarization of the three distinct SHG-active polyhedra, both induced by partial fluorine substitution on the [MoO6] octahedra.

Large Second-Harmonic Response and Giant Birefringence of CeF2(SO4) Induced by Highly Polarizable Polyhedra.

Second-harmonic generation (SHG) response and birefringence are two critically important properties of nonlinear optical (NLO) materials. However, the simultaneous optimization of these two key properties remains a major challenge because of their contrasting microstructure requirements. Herein, we report the first tetravalent rare-earth metal fluorinated sulfate, CeF2(SO4). Its structure features novel net-like layers constructed by highly distorted [CeO4F4] polyhedra, which are further interconnected by [SO4] tetrahedra to form a three-dimensional structure. CeF2(SO4) exhibits the strongest SHG effect (8 times that of KH2PO4) and the largest birefringence for sulfate-based NLO materials, the latter exceeding the birefringent limit for oxides. Theoretical calculations and crystal structure analysis reveal that the unusually large SHG response and giant birefringence can be attributed to the introduction of the highly polarizable fluorinated [CeO4F4] polyhedra as well as the favorable alignment of [CeO4F4] polyhedra and [SO4] tetrahedra. This research affords a new paradigm for the designed synthesis of high-performance NLO materials.

UV Solar-Blind-Region Phase-Matchable Optical Nonlinearity and Anisotropy in a π-Conjugated Cation-Containing Phosphate.

Wide ultraviolet (UV) transparency, strong second-harmonic generation (SHG) response, and sufficient optical birefringence for phase-matching (PM) at short SHG wavelengths are vital for practical UV nonlinear optical (NLO) materials. However, simultaneously optimizing these properties is a major challenge, particularly for metal phosphates. Herein, we report a non-traditional π-conjugated cation-based UV NLO phosphate [C(NH2 )3 ]6 (PO4 )2 ⋅3 H2 O (GPO) with a short UV cutoff edge. GPO is SHG active at 1064 nm (3.8 × KH2 PO4 @ 1064 nm) and 532 nm (0.3 × ß-BaB2 O4 @ 532 nm) and also possesses a significant birefringence (0.078 @ 546 nm) with a band gap >6.0 eV. The PM SHG capability of GPO can extend to 250 nm, indicating GPO is a promising UV solar-blind NLO material. Calculations and crystal structure analysis show that the rare coexistence of wide UV transparency, large SHG response, and optical anisotropy is due to the introduction of π-conjugated cations [C(NH2 )3 ]+ and their favorable arrangement with [PO4 ]3- anions.

Giant Optical Anisotropy in the UV-Transparent 2D Nonlinear Optical Material Sc(IO3 )2 (NO3 ).

Birefringence is a fundamental optical property for linear and nonlinear optical (NLO) materials. Thus far, it has proved to be very difficult to engineer large birefringence in optical crystals functioning in the UV region. Herein, we report the first 2D rare-earth iodate-nitrate crystal Sc(IO3 )2 (NO3 ) (SINO), which is shown to exhibit giant optical anisotropy. Air-stable SINO possesses a short UV absorption edge (298 nm), a strong NLO response (4.0 times that of benchmark KH2 PO4 ) for the nitrate family, and the largest birefringence (Δn=0.348 at 546 nm) of inorganic oxide optical crystals. The unusually large birefringence and NLO response can be attributed to an optimized 2D layered structure, combined with highly polarizable and anisotropic building units [IO3 ]- and [NO3 ]- . These findings will facilitate the development of UV linear and NLO materials with giant optical anisotropy and promote their potential application in optoelectronic devices.

Calix[8]arene Sulfonic Acid Catalyzed Three-Component Reaction for Convenient Synthesis of 3,4-Dihydropyrimidin-2(1H)-ones/thiones under Ultrasonic Irradiation.

In this work, the catalytic activity of calix[8]arene sulfonic acid was successfully investigated for the famous Biginelli reaction. Under ultrasonic irradiation, calix[8]arene sulfonic acid could efficiently catalyzed the three-component reaction of aldehydes with ethyl acetoacetate and urea or thiourea in ethanol to afford the corresponding 3,4-dihydropyrimidin-2(1H)-ones/thiones in 46-93%. The advantages of this method are the easy isolated procedure, short reaction time and low cost of the catalyst.

Complete Sets of Material Constants of [001]-Poled 0.72Pb(Mg1/3Nb2/3)O3- 0.28PbTiO3 Single Crystals Using Alternating Current Poling.

Alternating current poling (ACP) is an effective method to improve the piezoelectric performance of relaxor-PbTiO3 (PT) ferroelectric single crystal. 0.72Pb(Mg1/3Nb2/3)O3-0.28PbTiO3 (PMN-PT) single crystals have been used to fabricate piezoelectric transducers for medical imaging. Up to date, there are no reports about the full matrix material constants of PMN-0.28PT single crystals poled by ACP. Here, we report the complete sets of elastic, dielectric, and piezoelectric properties of [001]-poled PMN-0.28PT single crystals by direct current poling (DCP) and ACP through the resonance method. The results show that [001]-poled rhombohedral PMN-0.28PT single crystals exhibit the enhancement of longitudinal and transverse piezoelectric properties ( d33  âˆ¼ 2000 pC/N, d31  âˆ¼ -1010 pC/N) after ACP. Compared with DCP samples ( d33  âˆ¼ 1660 pC/N, d31  âˆ¼ -780 pC/N), the values of d33 and d31 increase 20% and 29%, respectively. While the d15 value decrease from 110 pC/N for DCP sample to 90 pC/N for ACP sample, showing the decrease in transverse shear piezoelectric properties. In addition, the elastic stiffness coefficients c11 , c12 , c13 , the elastic compliance coefficients s11 , s12 , and the dielectric constants ε11 , ε33 have great change compared with DCP and ACP samples. This variation of the property matrices provides a reference for high-performance piezoelectric device design.

Enhanced mechanical quality factor of BiScO3-PbTiO3 piezoelectric ceramics using glass composition.

Compared with pure Pb-based perovskite ferroelectric materials, Bi(Me)O3-PbTiO3 (Me = Sc3+, In3+, Yb3+) have attracted attention due to their remarkable advantage in their Curie temperature. Among them, BiScO3-PbTiO3 piezoelectric ceramic is a potential piezoelectric material in high-temperature applications for its high Curie temperature and excellent piezoelectric coefficient. However, its shortcomings are high dielectric loss and low mechanical quality factor. Herein, we report the improvement of the mechanical quality factor of 0.36BS-0.64PT ceramics through the addition of glass composition (GeO2). There is a small change in the Curie temperature after GeO2 addition. The piezoelectric coefficient d 33 and planar electromechanical coupling factor k p increase first and then decrease, and the mechanical quality factor Q m monotone increases with an increase in GeO2. The 0.36BS-0.64PT + 0.5 mol%GeO2 ceramics have optimal electrical properties with T C of 455 °C, d 33 of 385 pC N-1, k p of 58%, and Q m of 90. In addition, the thermal stability of 0.36BS-0.64PT + xGeO2 and 0.36BS-0.64PT ceramics is almost the same. It was concluded that the mechanical quality factor of BS-PT ceramics can be enhanced by the addition of GeO2 with other properties remaining unchanged.

Phosphogermanate Crystal: A New Ultraviolet-Infrared Nonlinear Optical Crystal with Excellent Optical Performances.

The phase matching ability is a key factor for nonlinear optical crystals to realize coherent output. Herein, a new design strategy combining ultraviolet and infrared functional groups into a ferroelectric was put forward. Thus, a phosphogermanate crystal, KGeOPO4, was designed and studied. It exhibits a wide transparency window (0.22-9.70 µm), a strong second harmonic generation response (5× KH2PO4), a high laser-induced damage threshold (1.61 GW/cm2), and the typical ferroelectricity (coercive field ∼ 9.8 kV/cm and remnant polarization ∼7.6 µC/cm2). In the infrared region, it could realize coherent output by the birefringence phase matching method, while it could generate ultraviolet coherent lights by the quasi-phase matching technique. Therefore, this work designs a promising ultraviolet-infrared nonlinear optical crystal and provides a new perspective for exploring nonlinear optical crystals.

Optimizing the Piezoelectric and Dielectric Properties of Pb(In1/2Nb1/2)O3-PbTiO3 Ferroelectric Crystals via Alternating Current Poling Waveform.

The alternating current poling (ACP) method has been attracting significant attention because of the enhanced piezoelectric and dielectric properties of relaxor-based ferroelectric (FE) crystals with advantages of high-efficiency, time-savings, and ease of operation. The most commonly used poling waveform is the bipolar triangle. Other waveforms have been seldom applied in ACP. However, the waveform plays a significant influence on the fatigue performance of FE materials. Therefore, optimizing the ACP waveform to gain high piezoelectric performance and decrease dielectric loss factors is technologically essential. Here, the effects of ACP waveforms on the piezoelectric and dielectric properties of [001]c-oriented 0.66 PIN-0.34 PT FE crystals were studied. The highest piezoelectric coefficient d33 (1450 pC/N) and dielectric permittivity εT33/ε0 (3180) were obtained using the sesquipolar triangle waveform while the lowest dielectric loss factors tan δ (0.99%) was obtained using the unipolar triangle waveform. FE hysteresis loop measurements revealed that the lower coercive field and current density are beneficial for higher piezoelectric performance. Domain analysis showed that ACP samples exhibit a regular domain structure and high density 109° domain walls, which are the critical reasons for enhanced piezoelectric performance. This work provides guidance in designing an ACP waveform to achieve higher performance.

π-Conjugated Trigonal Planar [C(NH2)3]+ Cationic Group: A Superior Functional Unit for Ultraviolet Nonlinear Optical Materials.

Employing π-conjugated anionic groups in molecular construction has been proven to be an effective strategy to find superior ultraviolet (UV) nonlinear optical (NLO) crystals over the decades. Herein, unlike the traditional π-conjugated anionic groups, we identify that a π-conjugated cationic group, viz., [C(NH2)3]+, is also an excellent UV NLO-active functional group in theory. Furthermore, we identify a [C(NH2)3]+-containing compound, C(NH2)3ClO4, as a promising UV NLO candidate due to its short UV cutoff edge (200 nm), remarkable second-harmonic generation effect (∼3 × KDP), and moderate birefringence of 0.076@1064 nm. Additionally, C(NH2)3ClO4 has excellent ferroelectric properties and reversal of domains, which also enables it to produce ultraviolet coherent light as short as 200 nm by a quasi-phase matching technique with a periodically poling method. Our study may provide not only a promising UV NLO crystal but also a new π-conjugated functional unit, [C(NH2)3]+, which will open a path to finding new classes of high-performance UV NLO crystals.

Effects of alternating current poling on the dielectric and piezoelectric properties of Pb(In0.5Nb0.5)O3-PbTiO3 crystals with a high Curie temperature.

The alternating current poling (ACP) method has been become more and more popular recently because of its advantages of being low cost, time saving and highly efficient. Few ACP studies have focused on relaxor-PT crystals with a high coercive field and high Curie temperature or the effects of ACP on intrinsic and extrinsic contributions. The effects of the electric field, frequency, and number of cycles of ACP on the piezoelectric and dielectric properties of 〈001〉-oriented Pb(In0.5Nb0.5)O3-PbTiO3 ferroelectric crystals were studied. The dielectric permittivity ε 33 T /ε 0 and piezoelectric coefficient d 33 of an ACP sample are 3070 and 1400 pC N-1, respectively, which are 14% and 18% larger than those of a DCP sample. Rayleigh analysis reveals that both intrinsic and extrinsic contributions are enhanced after ACP. The poling electric field, frequency and cycle number can influence the intrinsic and extrinsic contributions. The intrinsic contribution is significantly affected by the poling electric field, and cycle number, but it is not very sensitive to frequency, while the poling electric field, frequency and cycle number are very important for the extrinsic contribution. This work demonstrates that the uniform domain patterns are a critical factor for the enhancement of the piezoelectric properties.

Broad bandwidth emission and in situ electric field modulation of photoluminescence in Nd-doped ferroelectric crystals.

The electric field modulation of photoluminescence in ferroelectric-optical materials as a novel in situ, non-damaging and real-time controllable method has drawn much research focus. The broad bandwidth emission of 33 nm and a tuneable luminescence contrast of 28% were achieved in Nd-doped Pb(Mg1/3Nb2/3)O3-PbTiO3 (Nd:PMNT) tetragonal ferroelectric-optical crystals arising from spontaneous polarization. The study of Nd:PMNT ferroelectric crystals under a cyclic, triangular alternating current voltage wave showed that the change in the photoluminescence intensity subjected to an electric field is mainly related to the 180° domain distribution, rather than the 90° domain. The physical process of electric field tuning luminescence is to control the 180° domain distribution using the external electric field, which thereby effectively tunes the luminescence. This finding restricts the limitation of a specific phase change region, which greatly increases the range of materials used and has guiding significance for research in the electric field modulation of luminescent technology.

Novel noncentrosymmetric zinc coordination polymer containing an unusual zinc carboxylate-sulfonate substructure with a (10,3)-d topology and its second-harmonic-generation properties.

A novel 3D coordination polymer, Zn(2)(µ(2)-OH)(SIP)(DPP) (1), with mixed ligands of 5-sulfoisophthalate (SIP) and 1,3-di-4-pyridylpropane (DPP), has been hydrothermally synthesized and characterized. 1 contains an unusual 3D subnet with distorted (10,3)-d topology and left/right-handed helical channels. Second-harmonic-generation (SHG) measurements revealed that the material has a strong SHG response (∼2.5 times that of potassium dihydrogen phosphate (KDP)) and is phase-matchable. In addition, photoluminescent and thermogravimetric analysis were also performed on 1.

Electrical properties of Sb2O3-modified BiScO3-PbTiO3-based piezoelectric ceramics.

Compared with pure Pb-based perovskite ferroelectric materials, BiMeO3-PbTiO3 (Me = Sc3+, In3+, and Yb3+) systems have remarkable advantages in their Curie temperatures. As a member of this group, the BiScO3-PbTiO3 (BS-PT) solid solution has drawn considerable attention from scientists for its high Curie temperature and excellent piezoelectric coefficient. However, BS-PT ceramics still have some shortcomings, such as high dielectric loss and low mechanical quality factor, which make them unsuitable for high-temperature applications. Herein, we report the effect of the addition of complex ions on the electrical properties of BS-PT ceramics. Sb2O3-doped 0.36BiScO3-0.64PbTi0.97Fe0.03O3 + 1 mol% MnO2 (BS-PTFMn + x% Sb2O3) ceramics were fabricated and their electrical properties were studied. BS-PTFMn + 0.75% Sb2O3 had an optimal piezoelectric coefficient, exhibiting which indicates that Sb2O3 doping can improve the piezoelectric properties of the BS-PT ceramics, exhibiting a "soft" effect of Sb2O3 doping. In addition, the thermal depolarization temperature (T d) of BS-PTFMn + 0.75% Sb2O3 ceramics remained above 300 °C, such as 325 °C for BS-PTFMn + 0.75% Sb2O3. It was concluded that the piezoelectric properties of BS-PT ceramics were enhanced by the addition of Sb2O3.

Enhanced Energy Storage Density of Lead Lutetium Niobate Crystals by Electric Field-Induced Secondary Phase Transition via Na/La Codoping.

As emerging materials for capacitor applications, antiferroelectric (AFE) materials possess high energy storage density. AFE single crystals are conducive to studying the physical mechanism of AFE response. However, the preparation of AFE single crystals is a huge and long-standing challenge. Herein, we report the effect of Na/La codoping on the energy storage properties and phase transition of Pb(Lu1/2Nb1/2)O3 (PLN) AFE single crystals. An enhanced recoverable energy storage density of 4.81 J/cm3 with a high energy efficiency of 82.36% is obtained, which is much larger than that of the PbZrO3- and PLN-based AFE crystals. Two superlattice reflections, which stem from the A-site Pb2+ ions and the ordered B-site ions, are identified by X-ray diffraction and selected-area electron diffraction. The domain structures demonstrated a high temperature stability of the AFE phase. A secondary ferroelectric phase transition is induced after codoping, resulting in a sharp improvement of polarization (12.5 µC/cm2), which contributes to the enormous enhancement of energy storage density. This multiphase transition is explained using the modified Ginzburg-Landau-Devonshire phenomenology.

Ca2B5O9Cl and Sr2B5O9Cl: Nonlinear Optical Crystals with Deep-Ultraviolet Transparency Windows.

M2B5O9X is a prominent family with excellent nonlinear optical (NLO) responses, just as the Pb2B5O9I crystal with a large second harmonic generation (SHG) of 13.5 times that of KH2PO4. However, most of these compounds are limited to ultraviolet and visible regions because of their long absorption edge (small band gap). Here, we report two members of this family, which change the situation. Using a high-temperature solution method, we obtain Ca2B5O9Cl and Sr2B5O9Cl crystals, which exhibit a deep-ultraviolet (DUV) absorption edge of 170 nm (band gap ≈ 7.29 eV). It is an important breakthrough in the DUV transparency of the M2B5O9X family. Furthermore, Ca2B5O9Cl crystals display a phase-matching SHG response under a 1064 nm laser, which is further confirmed by the balance between the suitable birefringence and the small dispersion of refractive indexes in the wavelength range of 1064-532 nm. Therefore, they are promising DUV transparency windows and NLO candidates.

A new iodate-phosphate Pb2(IO3)(PO4) achieving great improvement in birefringence activated by (IO3)- groups.

The first divalent-metal iodate-phosphate, Pb2(IO3)(PO4), has been prepared via the strategy of introducing (IO3)- into phosphate. The structure features a unique 3D network where [Pb(IO3)]∞+ and [Pb(PO4)]∞- layers are alternatively interconnected. The birefringence of Pb2(IO3)(PO4) is greatly increased to 0.060 at 1064 nm.

Zn3B7O13Cl: A New Deep-Ultraviolet Transparency Nonlinear Optical Crystal with Boracite Structure.

Nonlinear optical crystals play important roles in modern laser science and technology. However, the design and growth of new nonlinear optical (NLO) materials is still a challenging issue for researchers. Due to the excellent performance of Mg3B7O13Cl crystal, we paid attention to the optimization of its structure, in order to find new NLO materials with favorable properties. Here, Zn3B7O13Cl crystals were obtained by a high-temperature solution method. Its structure was determined to be the trigonal symmetry with a polar space group of R3c, which is more highly symmetric than that of Mg3B7O13Cl (Pca21). The experimental and theoretical investigations demonstrated that the title compound exhibits a short absorption cutoff (band gap ∼6.53 eV), moderate SHG responses (2.2 times that of KDP at 1064 nm), and the improved birefringence, which results from the large distortion and anisotropy of borate groups and zinc polyhedrons. Therefore, the structural modification of Mg3B7O13Cl by zinc cations achieves a balance between the deep-ultraviolet transparency, the nonlinear optical effect, and the moderate birefringence, which is very significant for the design of practical NLO materials.