Borate-Based Ultraviolet and Deep-Ultraviolet Nonlinear Optical Crystals

K3Y3(BO3)4: A Potential UV Nonlinear-Optical Crystal Designed by a Chemical Substitution Strategy

Nonlinear-optical (NLO) crystals capable of controlling and manipulating light to generate coherent radiation at challenging wavelengths are of significant interest. However, designing a new UV NLO crystal remains difficult due to the rigid requirements for structure and properties. Herein, we have successfully designed and synthesized a novel noncentrosymmetric (NCS) rare-earth borate UV NLO crystal, K3Y3(BO3)4, through the heterovalence substitution of YAl3(BO3)4. K3Y3(BO3)4 (KYBO) crystallizes in the NCS and polar space group of P63mc, with the structure formed by the interconnectioned BO3 triangles and YO8 polyhedra through corner-sharing and edge-sharing. The property measurements indicate that KYBO is second-harmonic-generation-active with a moderate response, ∼2 × KDP. Meanwhile, KYBO can exhibit a short UV cutoff edge (λcutoff < 190 nm), indicating its potential as a new UV or deep-UV NLO crystal.

Electronic, optical and spectroscopic properties of N-dialkyl-imidazolium hexafluorophosphate (CNMIM.PF6) ionic liquid crystal molecules investigated by computational methods

In this present work, we calculate the electronic, spectroscopic and nonlinear optical properties (NLO) of N-dialkyl-imidazolium hexafluorophosphate (CNMIM.PF6, where N = 10, 12, 14, 16, 18, 20) ionic liquid crystal molecules under the effect of alkyl chain length variation in cation moiety [CNMIM]+ with fixed anion [PF6]-. CONTEXT: The majority of research on ionic liquid crystal to date has been focused on experiments, while theoretical studies on the optical properties of ionic liquid crystal have been extremely rare. Nonlinear phenomena in optical devices have attracted many researchers. Therefore, results of NLO properties may favor facile synthesis and fabrication of novel-type of materials as well as optoelectronic devices. Spectroscopic studies elucidate further insight into ionic liquid crystal behavior. The results demonstrate that variations in alkyl chain length have an impact on the conformers' electrical, spectroscopic, and NLO properties as well as their stability. The stability of ionic liquid crystal molecules increases with increase in the alkyl chain length and the energy band gap range is 6.64-6.29 eV. Understanding ionic liquid crystal's physical behavior requires an understanding of their dipole moments and NLO features, which are covered in this article. The results of NLO characteristics for all ionic liquid crystal molecules show that their first-order hyperpolarizabilities are higher than the reference molecule (urea). METHODS: The electronic (molecular energy band gap, electrostatic potential map, as well as HOMO-LUMO orbitals) and spectroscopic (IR-RAMAN, UV) properties were evaluated with the help of theoretical model at B3LYP/6-31G(d) while the NLO study has been performed using B3LYP and M06-2X with different basis sets 6-31G(d) and 6-311++G(d,p), as implemented in Gaussian09 software.

Synergistic Effect of π-Conjugated [C(NH2)3] Cation and Sb(III) Lone Pair Stereoactivity on Structural Transformation and Second Harmonic Generation

The search for nonlinear optical (NLO) crystals with excellent comprehensive properties is a formidable challenge. In this work, two guanidine antimony fluorides, C(NH₂)₃Sb₂F₇ and C(NH₂)₃SbF₄, were obtained by conjunction of [C(NH₂)₃] groups with π-conjugated configuration and stereochemically active Sb³⁺ cations. Due to the different coordination modes of Sb-F bonds and H-F hydrogen bonds, the crystal structure of C(NH₂)₃Sb₂F₇ is centrosymmetric (CS), while C(NH₂)₃SbF₄ is noncentrosymmetric (NCS). Optical measurements show that the UV cutoff wavelengths of the title compounds were both less than 240 nm. Thermal studies indicate that these crystals are stable up to 250 °C. In addition, the second harmonic generation (SHG) response of C(NH₂)₃SbF₄ is 2 times that of KH₂PO₄ (KDP) with the phase-matchable capacity. Theoretical calculations reveal that the large SHG effects of C(NH₂)₃SbF₄ were attributed to the synergy between the planar [C(NH₂)₃] units and the distorted [SbF₄] groups. These results demonstrate that the guanidine antimony fluorides will have potential value as UV NLO materials.

A General Principle for DUV NLO Materials: π-Conjugated Confinement Enlarges Band Gap*

Current nonlinear optical materials face a conventional limitation in the trade-off between the band gap and birefringence, especially in the deep UV spectral region. To circumvent this dilemma, we propose a general principle, π-conjugated confinement, to partially decouple the interunit π-conjugated interactions by the separation of non-π-conjugated units. The goal is to further enlarge the band gap to a value larger than that of the singular π-conjugated counterpart and to maintain a suitable density of π-conjugated units to gain a large optical anisotropy. We reveal that π-conjugated confinement is a shared structural feature for all DUV NLO materials known to date, and thus, it provides a novel and essential design criterion for future design synthesis. Guided by this principle, the carbonophosphates are predicted to be a new promising DUV candidate system. Sr₃ Y[PO₄ ][CO₃ ]₃ (1) and Na₃ X[PO₄ ][CO₃ ] (X=Ba, Sr, Ca, Mg, 2-5) exhibit not only greatly enhanced birefringence that is 3-24 times larger than that of singular phosphates but also enhanced band gaps that are 0.2-1.7 eV wider than those of singular carbonates.

Synthesis, crystal structure and luminescence properties of a new samarium borate phosphate, CsNa2Sm2(BO3)(PO4)2

A new caesium sodium samarium borate phosphate, CsNa₂Sm₂(BO₃)(PO₄)₂, has been obtained successfully by the high-temperature solution growth (HTSG) method and single-crystal X-ray diffraction analysis reveals that it crystallizes in the orthorhombic space group Cmcm. The structure contains BO₃, PO₄, NaO₇ and SmO₇ polyhedra which are interconnected via corner- or edge-sharing O atoms to form a three-dimensional [Na₂Sm₂(BO₃)(PO₄)₂]_∞ network. This network delimits large cavities where large Cs⁺ cations reside to form the total structure. Under 402 nm light excitation, CsNa₂Sm₂(BO₃)(PO₄)₂ exhibits three emission bands due to the 4f→4f transitions of Sm³⁺. Furthermore, we introduced Gd³⁺ into Sm³⁺ sites to optimize the Sm³⁺ concentration and improve the luminescence intensity. The optimal concentration is Gd/Sm = 98/2. The luminescent lifetime of a series of CsNa₂Gd_2(1-x)Sm_2x(BO₃)(PO₄)₂ phosphors shows a gradual degradation of lifetime from 2.196 to 0.872 ms for x = 0.01-0.10. The Commission Internationale de l'Eclairage (CIE) 1931 calculation reveals that CsNa₂Gd_1.96Sm_0.04(BO₃)(PO₄)₂ can emit orange light under 402 nm excitation.

Bismuth-Based Oxyborate Piezoelectric Crystals: Growth and Electro-Elastic Properties

The non-centrosymmetric bismuth-based oxyborate crystals have been extensively studied for non-linear optical, opto-electric and piezoelectric applications. In this work, single crystal growth and electro-elastic properties of α-BiB3O6 (α-BIBO) and Bi2ZnB2O7 (BZBO) crystals are reported. Centimeter-sized α-BIBO and BZBO crystals were grown by using the Kyropoulos method. High resolution X-ray diffraction tests were performed to assess the crystal quality. The full-width at half-maximum values (FWHM) of the rocking curves were evaluated to be 35.35 arcsec and 47.85 arcsec for α-BIBO and BZBO samples, respectively. Moreover, the electro-elastic properties of α-BIBO and BZBO crystals are discussed and summarized, based on which the radial extensional and the face shear vibration modes were studied for potential acoustic device applications. The radial extensional mode electro-mechanical coupling factors kp were evaluated and found to be 32.0% and 5.5% for α-BIBO and BZBO crystals, respectively. The optimal crystal cuts with face shear mode were designed and found to be (YZt)/−53° (or (YZt)/37° cut) for α-BIBO crystal, and (ZXt)/±45° cut for BZBO crystal, with the largest effective piezoelectric coefficients being in the order of 14.8 pC/N and 8.9 pC/N, respectively.

Thermal properties and CW laser performances of pure and Nd doped Bi2ZnB2O7 single crystals

The CW laser performances are realized along the optical axes of Nd:BZBO single crystals.

Ba2ZnSc(BO3)3and Ba4Zn5Sc2(BO3)8: first examples of borates in the Zn–Sc–B–O system featuring special structure configurations

First examples in the Zn–Sc–B–O system featuring a special Zn/Sc–O configuration ([Zn₂(BO₃)₆]¹⁴⁻cluster, lowest-coordinated ScO₅polyhedra, and coexistence of ZnO₄and ZnO₆units).

Lithium borate Li3B5O8(OH)2 with large second harmonic generation and a high damage threshold in the deep-ultraviolet spectral range

The electronic structure and linear and nonlinear optical susceptibility dispersions of lithium borate Li₃B₅O₈(OH)₂ are comprehensively investigated. The investigation is achieved on Li₃B₅O₈(OH)₂ in the form of single crystals, taking into account the influence of the packing of the structural units on the linear and nonlinear optical susceptibility dispersion. The calculations highlight that the BO₃ structural unit packing is the main source of the large birefringence in Li₃B₅O₈(OH)₂ due to the high anisotropic electron distribution, and, hence, it affects the macroscopic second harmonic generation (SHG) coefficients. This work provides a new path for the design of UV-NLO materials with high SHG efficiencies and short cutoff edges by introducing an alkali metal into borates. The large SHG is due to hyperpolarizability formed by co-parallel BO₃ triangle groups. The absorption edge of Li₃B₅O₈(OH)₂ occurs at λ = 190 nm and the optical band gap is estimated to be 6.52 eV, which is in good agreement with the experimental data (6.526 eV). The energy gap value confirms that Li₃B₅O₈(OH)₂ exhibits an exceptional laser damage threshold and is expected to produce coherent radiation in the deep-ultraviolet (DUV) region. The obtained value of SHG at λ = 1064 nm is about 1.5 times that of the well-known NLO crystal KH₂PO₄ (KDP) at λ = 1064 nm and 3.5 times that of KDP at λ = 190 nm, which is transparent down to the DUV region. Thus, one can conclude that the combination of an alkali metal with borates leads to the generation of promising DUV-NLO crystals. This work is aimed at qualitative and quantitative investigation to report a reliable SHG value and provide details of the NLO tensor for bulk Li₃B₅O₈(OH)₂ single crystals.

Polar phase transitions in heteroepitaxial stabilized La0.5Y0.5AlO3 thin films

We report on the fabrication of epitaxial La_0.5Y_0.5AlO₃ ultrathin films on (001) LaAlO₃ substrates. Structural characterizations by scanning transmission electron microscopy and x-ray diffraction confirm the high quality of the film with a ^- b ⁺ c ^- AlO₆ octahedral tilt pattern. Unlike either of the nonpolar parent compound, LaAlO₃ and YAlO₃, second harmonic generation measurements on the thin films suggest a nonpolar-polar phase transition at T _c near 500 K, and a polar-polar phase transition at T _a near 160 K. By fitting the angular dependence of the second harmonic intensities, we further propose that the two polar structures can be assigned to the Pmc2 ₁ and Pmn2 ₁ space group, while the high temperature nonpolar structure belongs to the Pbnm space group.