Hydroxyl-Driven Enhanced Birefringence in Borophosphates

Borophosphates have become promising candidates for ultraviolet or deep-ultraviolet functional crystals. Through high-temperature solution method, four new borophosphates, K2B2P2O9, (NH4)2BP2O7(OH), K2BP2O7(OH), and P21/c-(NH4)2B2P3O11(OH), were acquired successfully. Single crystal X-ray diffraction suggests that K2B2P2O9, (NH4)2BP2O7(OH), and K2BP2O7(OH) belong to the noncentrosymmetric space group, while P21/c-(NH4)2B2P3O11(OH) belongs to the centrosymmetric compound. It is worth mentioning that K2B2P2O9, (NH4)2BP2O7(OH), and K2BP2O7(OH) present the new fundamental building blocks [B2P2O11], [BP2O10H], and [BP2O9(OH)], respectively, as far as we know. Compared with K2B2P2O9, (NH4)2BP2O7(OH), K2BP2O7(OH), and P21/c-(NH4)2B2P3O11(OH) exhibit a larger optical anisotropy, further confirming the positive effect of hydroxyl groups on birefringence. UV-vis-NIR diffuse reflectance spectra display that K2B2P2O9 and (NH4)2BP2O7(OH) have short UV cutoff edges. Meanwhile, theoretical calculations were conducted to comprehend their optical properties and electronic structures.

Rational Design of the First Ammonium Magnesium Borate with Deep-Ultraviolet Cutoff Edge and Moderate Birefringence and Further Investigation into the Nature of Ammonium in the Borate System

Through the rational design of the experimental method, the first combination of ammonium and magnesium in the borate system was successfully achieved. In this paper, a case of ammonium magnesium borate, (NH₄)₂{Mg(H₂O)₂[B₆O₇(OH)₆]₂}·2H₂O, was successfully synthesized by a mild hydrothermal method at a relatively low temperature. A brief review was performed to show the participation of NH₄⁺ in the recent development of optical materials. By discussing the optimum synthesis method of ammonium-containing borates and the main factors affecting the dimensionality of B-O anionic groups in their structures, the design strategy for synthesizing ammonium-containing borate and adjusting its structure has been put forward. Relevant experimental measurement results and the first-principles calculation results show that the title compound has a deep-UV cutoff edge (<200 nm) and moderate birefringence (Δn_cal. = 0.064 @546 nm), which indicates its potential application in the deep-UV region.

SbI3·3S8: A Novel Promising Inorganic Adducts Crystal for Second Harmonic Generation

In the past twenty years, the basic investigation of innovative Non-Linear Optical (NLO) crystals has received significant attention, which has built the crucial heritage for the use of NLO materials. Fundamental research is essential given the scarcity of materials for NLO compounds, especially in the deep ultraviolet (DUV) and middle- and far-infrared (MFIR) regions. In the present work, we synthesized high-quality MFIR SbI₃·3S₈ NLO crystals having a length in the range of 1-5 mm through rapid facile liquid phase ultrasonic reaction followed by the assistance of instantaneous natural evaporation phenomenon of the solvent at room temperature. X-ray diffraction (XRD) results ratify the hexagonal R3m structure of SbI₃·3S₈ crystal, and energy-dispersive X-ray spectroscopy (EDX) demonstrates that the elemental composition of SbI₃·3S₈ crystal is similar to that of its theoretical composition. The direct and indirect forbidden energy gaps of SbI₃·3S₈ were measured from the optical transmittance spectra and they were shown to be 2.893 eV and 1.986 eV, respectively. The green sparkling signal has been observed from the crystal during the second harmonic generation (SHG) experiment. Therefore, as inorganic adducts are often explored as NLO crystals, this work on the MFIR SbI₃·3S₈ NLO crystal can bring about additional investigations on this hot topic in the near future.

BaB2P2O8F2: A Fluoroborophosphate with [B2P2O8F2]∞ Layers and Deep-Ultraviolet Cutoff Edge

A fluoroborophosphate, BaB₂P₂O₈F₂, was successfully obtained. Its structure contains a novel [B₂P₂O₈F₂]_∞ layer containing six-membered rings, which is formed by the fundamental building block composed of three types of non-π-conjugated groups, [PO₄], [BO₄], and [BO₂F₂]. BaB₂P₂O₈F₂ has a deep-ultraviolet (DUV) cutoff edge (λ < 200 nm) and a tiny birefringence (Δn = 0.007 at 532 nm), which originates from the constituent non-π-conjugated groups. The title compound enriches the versatility of the fluoroborophosphates, encouraging further research into DUV materials in fluoroborophosphate systems.

Analysis of the growth and physicochemical properties of the newly developed stilbazolium derivative 4-N,N-dimethylamino-4-N-methyl stilbazolium 2-formyl benzene sulfonate (DSFS) single crystal: an effective material for nonlinear optical applications

A novel ionic stilbazolium derivative single crystal of 4-N,N-dimethylamino-4-N-methyl stilbazolium 2-formyl benzene sulfonate (DSFS) was successfully cultivated with methanol as the solvent by using the slow evaporation technique. Structural confirmation was done using single-crystal X-ray diffraction (SCXRD), and the obtained results reveal that the DSFS crystal crystallized in a centrosymmetric pattern with P1̄ space group. The presence of different vibrational modes in the DSFS crystal is affirmed via Fourier transform infrared (FTIR) spectroscopy. Linear optical constants such as cut-off wavelength, bandgap, extinction coefficient, Urbach energy, electrical conductivity and optical conductivity of the titular crystal were found from ultraviolet–visible–near infra-red spectroscopy (UV-Vis-NIR). The emission wavelength of the title crystal lies in the red region (620 nm), which was confirmed from the photoluminescence spectroscopy (PL). The surface nature of the grown ionic crystal was examined through the etching and atomic force microscopy (AFM) technique. With a He–Ne laser as the source, Z scan analysis was carried out to study the third-order nonlinear properties of the DSFS crystal.

The newly grown stilbazolium derivative 4-N,N-dimethylamino-4-N-methyl stilbazolium 2-formyl benzene sulfonate (DSFS) single crystal can be used for multiple applications such as optoelectronics, photonics and nonlinear applications.