Optical Crystals Research Articles

Giant Mid-Infrared Second-Harmonic Generation Response in a Densely-Stacked Van Der Waals Transition-Metal Oxychloride.

Second-harmonic generation (SHG) is a fundamental optical property of nonlinear optical (NLO) crystals. Thus far, it has proved difficult to engineer large SHG responses, particularly in the mid-infrared region, owing to the difficulty in simultaneously controlling the arrangement and density of functional NLO-active units. Herein, a new assembly strategy employing functional modules only, and aimed at maximizing the density and optimizing the spatial arrangement of highly efficient functional modules, has been applied to the preparation of NLO crystals, affording the van der Waals crystal MoO2 Cl2 . This exhibits the strongest powder SHG response (2.1×KTiOPO4 (KTP) @ 2100 nm) for a transition-metal oxyhalide, a wide optical transparency window, and a sufficient birefringence. MoO2 Cl2 is the first SHG-active transition-metal oxyhalide effective in the infrared region. Theoretical studies and crystal structure analysis suggest that the densely packed, optimally-aligned [MoO4 Cl2 ] modules within the two-dimensional van der Waals layers are responsible for the giant SHG response.

A methodical investigation on the growth and characterization of a third-order nonlinear optical novel co-crystal of 8-hydroxyquinolinium phthalate: X-ray, Hirshfeld surface, optical, mechanical, thermal and DFT analysis

A novel non-linear optical single crystal of 8-hydroxyquinolinium phthalate has been as-synthesised by a slow evaporation solution growth technique. Single-crystal X-ray diffraction analysis affirms that it belongs to a monoclinic crystal system. While UV–visible spectroscopy shows its optical transparency with a direct band gap of 2.80 eV, a photoluminescence study confirms a principal yellow emission at 370 nm excitation. Furthermore, the mechanical and thermal properties along with the functional groups’ study have also been laid out in this paper. Intermolecular interactions present in the crystal are ascertained from Hirshfeld surface and fingerprint plot studies. The Z-scan technique has reportedly affirmed third harmonics generation in the same. Theoretical calculations using DFT modelling further testify to the experimental observations thereby laying out the framework of the mentioned crystal in terms of its optimized geometry, molecular electrostatic potential, frontier molecular orbital, natural bond orbital and natural population analysis along with vibrational assignments and UV absorption analysis.

ASn(C10H12N2O8)Cl·H2O (A = K, Rb): Nonlinear optical crystals with new distorted Sn(IV)-centered nitrogen-oxygen-chloride polyhedron and wide band gaps

Nonlinear optical (NLO) crystals are the core components of laser for their capability of frequency conversion, so it is an important task to develop NLO crystals with excellent performance. Herein, we report two unique NLO crystals containing the Sn(IV) atom, ASn(C10H12N2O8)Cl·H2O (A = K, Rb). Both of them have been rationally synthesized by simultaneously introducing three coordination atoms with different electronegativities into the Sn(IV)-centered polyhedron. The arrangement of distorted [SnO4N2Cl] polyhedrons displays in an ordered phenomenon. They exhibit a phase-matching second-harmonic generation (SHG) response of 0.5 × KDP and wider band gaps than 4.2 eV Remarkably, KSn(C10H12N2O8)Cl·H2O and RbSn(C10H12N2O8)Cl·H2O possess large laser damage thresholds of 177 and 129 MW/cm2, respectively. Systematic studies reveal that the oriented arrangement of the distorted [SnO4N2Cl] polyhedrons makes the main contribution to their SHG response. This research provides an effective method for the exploration of NLO crystals in the future.

Heterologous Isomorphic Substitution Induces Optical Property Enhancement for Deep-UV Crystals: a Case in Rb[B3O3F2(OH)2

Optical anisotropy is pivotal for optical crystals, and it can be characterized by the maximum algebraic difference in refractive indices. Improving the optical anisotropy, especially for deep-ultraviolet (UV) crystals, is still a challenge and of interest. Herein, a new hydroxyfluorooxoborate, Rb[B3O3F2(OH)2], was obtained by the heterologous isomorphic substitution strategy. Dual enhancement for the band gap and birefringence compared with the parent A[B3O3F2(OH)2] (A = [Ph4P]/[Ph3MeP]) compounds was achieved in Rb[B3O3F2(OH)2]. This considerable enhancement originates from the removal of organic components and the retention of a birefringence-active anionic framework. This enhancement pushes the application region from UV to deep-UV. This discovery not only expands the structural chemistry of borates but also demonstrates the viability of heterologous isomorphic substitution to design deep-UV crystals with enhanced optical property.

Supramolecular Assemblies of Melamine-2-Thiobarbiturate and Melamine-Barbiturate-2-Thiobarbiturate: Experimental and Theoretical Studies

In this work, we considered the formation of supramolecular assemblies of melamine-thiobarbiturate and melamine-barbiturate-thiobarbiturate. It is known that thiobarbituric acid can form many tautomers, as well as different motifs due to the change of C2=O to C2=S hydrogen bonds. We formed the crystal. The resulting crystals were studied with scanning electron microscopy (SEM), optical fluorescence microscopy, single crystal and powder (PXRD) X-ray diffraction analyses, and solid state nuclear magnetic resonance (ss NMR). These systems were theoretically studied using density functional theory (DFT) and classical molecular dynamics (MD) simulations. Interestingly, just as in the case of melamine barbiturate, during the crystallization process, hydrogen from the C5 moiety of thiobarbituric acid migrates to the melamine molecule. In addition, the resulting melamine thiobarbiturate crystals exhibit fluorescence behavior in the red region (~565–605 nm), while the melamine barbiturate crystals are fluorescent in the green region (512–542 nm).

Mid-infrared Spectrally Pure Single-Photon States Generation from 22 Nonlinear Optical Crystals

We theoretically investigate the preparation of pure-state single-photon source from 14 birefringent crystals (CMTC, THI, LiIO3, AAS, HGS, CGA, TAS, AGS, AGSe, GaSe, LIS, LISe, LGS, and LGSe) and 8 periodic poling crystals (LT, LN, KTP, KN, BaTiO3, MgBaF4, PMN-0.38PT, and OP-ZnSe) in a wavelength range from 1224 nm to 11650 nm. The three kinds of group-velocity-matching (GVM) conditions, the phase-matching conditions, the spectral purity, and the Hong-Ou-Mandel interference are calculated for each crystal. This study may provide high-quality single-photon sources for quantum sensing, quantum imaging, and quantum communication applications at the mid-infrared wavelength range.

New group of inorganic salts of 1,3-diaminoguanidinium(1+) cation – crystal structures, vibrational spectra, linear and nonlinear optical properties

In the search for new molecular crystals for nonlinear optics (NLO), nine inorganic salts containing the 1,3-diaminoguanidinium(1+) cation as a promising organic “Y-aromatic” carrier of NLO properties were prepared and studied. Crystal structures of eight new salts, namely 1,3-diaminoguanidinium(1+) chloride (P21/c), hypophosphite (P21/c), hydrogen phosphite (P-1), dihydrogen phosphate (P21/c), hydrogen phosphate (P21/m), nitrite (P-1), sulfite (Pbcm) and chlorate (P21/c) were solved by the single crystal X-ray diffraction. The crystal structures contain centrosymmetric arrangements of pairs of counterions assembled into hydrogen-bonded undulated sheets. The charge-assisted hydrogen bonds in the resulting hydrogen bond networks are accommodated by the conformation of the 1,3-diaminoguanidinium(1+) cation as a hydrogen bond donor. All salts were also characterized by powder X-ray diffraction. The vibrational spectra (FTIR and Raman) were studied for all newly prepared salts and the previously published non-centrosymmetric sulfate (P6122). The assignment of the vibrational bands of these hydrogen-bonded crystals is derived from quantum-chemical computations (B3LYP/6-311G+(d,p) along with the Potential Energy Distribution analysis) concerning isolated 1,3-diaminoguanidinium(1+) cation and the results of correlation analysis involving present inorganic anions. The linear and nonlinear optical properties of the only non-centrosymmetric salt – 1,3-diaminoguanidinium sulfate – were studied. This uniaxial positive crystal is optically transparent down to 230 nm, and refractive indices (ne = 1.65 and no = 1.56) have been determined at 532 nm. The dispersion curves of the refractive indices were also calculated by the Q(LFT) procedure in the 532–1907 nm region. The experimentally determined (using 800 and 1000 nm laser irradiation) very low efficiency of second harmonic generation (i.e., ∼1% of KDP), which is consistent with the Kleinman symmetry assumption for the P6122 space group, limits further use of this crystal for second-order NLO applications.

Locations of the energy levels of lanthanide ions in Gd2O3 single crystals

Large-sized, high optical quality Gd2O3 single crystals were grown from a solution at T = 1145 °C using Czochralski method. XRD analysis showed that the crystal structure is characterized by a single cubic (bixbyite) phase (c-phase). The absorption spectra and luminescence properties of Gd2O3 doped with Eu3+ and Tb3+ impurity ions were studied. The absorption spectrum of Gd2O3:Eu in the short wavelength region is mainly due to charge transfer transitions from O2− to Eu3+ (240–290 nm), which overlap with the Urbach tail of the host-absorption. Additionally, electronic transitions in Eu3+ (320–540 nm) and Gd3+ (245–315 nm) lanthanide ions contribute to the absorption spectrum. Intraconfigurational radiative f – f transitions in impurity ions are clearly observed upon both UV- and X-ray excitations. However, 6PJ → 8S7/2 radiative transitions in Gd3+ ions are completely unobservable. Based on the obtained spectroscopic data, the energy positions of the ground state of all di- and trivalent lanthanide ions, as well as the energies of intraconfigurational f – f and interconfigurational f – d electronic transitions in Gd2O3 crystals with a cubic structure, are calculated. The proposed electronic energy diagram is used to discuss efficient energy transfer between lanthanide ions.

Quadruple‐Bidentate Nitrate‐Ligated A2Hg(NO3)4 (A=K, Rb): Strong Second‐Harmonic Generation and Sufficient Birefringence

AbstractThe design of efficient nonlinear optical (NLO) crystals continues to pose significant challenges due to the difficulty of assembling polar NLO‐active modules in an optimal additive fashion. We report herein the first NLO‐active mercuric nitrates A2Hg(NO3)4 (A=(KHNO), Rb (RHNO)), for which assembly is induced by ionic polarization of the d10 cations. The two new crystalline compounds are isostructural, featuring interesting pseudo‐diamond‐like structures with parallel [Hg(NO3)4] modules, and leading to strong powder second‐harmonic generation (SHG) responses of 9.2 (KHNO) and 8.8 (RHNO) times that of KH2PO4. In combination with the simple solution preparation of centimeter‐scale crystals, sufficient birefringence, and short ultraviolet (UV) cutoff edges, these attributes make KHNO and RHNO promising candidates for UV NLO materials. Theoretical calculations and single‐crystal structure analysis reveal that the newly‐developed highly condensed and distorted [Hg(NO3)4] module, with an Hg2+ cation that is quadruply bidentate nitrate‐ligated, is crucial for the significant SHG responses. This work highlights the potential importance of modules with multiple bidentate ligands for the development of high‐performing next‐generation NLO materials.

Quadruple-Bidentate Nitrate-Ligated A2 Hg(NO3 )4 (A=K, Rb): Strong Second-Harmonic Generation and Sufficient Birefringence.

The design of efficient nonlinear optical (NLO) crystals continues to pose significant challenges due to the difficulty of assembling polar NLO-active modules in an optimal additive fashion. We report herein the first NLO-active mercuric nitrates A2 Hg(NO3 )4 (A=(KHNO), Rb (RHNO)), for which assembly is induced by ionic polarization of the d10 cations. The two new crystalline compounds are isostructural, featuring interesting pseudo-diamond-like structures with parallel [Hg(NO3 )4 ] modules, and leading to strong powder second-harmonic generation (SHG) responses of 9.2 (KHNO) and 8.8 (RHNO) times that of KH2 PO4 . In combination with the simple solution preparation of centimeter-scale crystals, sufficient birefringence, and short ultraviolet (UV) cutoff edges, these attributes make KHNO and RHNO promising candidates for UV NLO materials. Theoretical calculations and single-crystal structure analysis reveal that the newly-developed highly condensed and distorted [Hg(NO3 )4 ] module, with an Hg2+ cation that is quadruply bidentate nitrate-ligated, is crucial for the significant SHG responses. This work highlights the potential importance of modules with multiple bidentate ligands for the development of high-performing next-generation NLO materials.

NaCl·CH4N2O·H2O: An Organic-Inorganic Hybrid Ultraviolet Nonlinear Optical Crystal with Optimized Comprehensive Properties.

Ultraviolet (UV) nonlinear optical (NLO) crystals are a vital component in laser systems to modulate frequency. Organic groups have the advantages of easy synthesis, structural diversity, and large hyperpolarizations (β), which can be combined with inorganic groups to form unique organic-inorganic hybrid NLO crystal materials. Herein, a urea-containing crystal NaCl·CH4N2O·H2O is screened out and large-size crystals have been grown by a simple aqueous solution method. Compared with most reported organic-inorganic hybrid NLO materials, it has optimized comprehensive properties including a large SHG effect of 1.53 × KDP, a moderate birefringence (0.084@1064 nm), and a short UV cutoff edge of 209 nm. First-principles studies reveal that the dominant contributor to the linear and nonlinear optical properties is the urea molecule.

Synthesis, Structural, Spectroscopic and Quantum Chemical Investigation of a Novel 1,4-Diamino-2,5-dichlorobenzenium Picrate Single Crystal: An Efficient NLO Material

A new organic nonlinear optical single crystal, 1,4-diamino-2,5-dichlorobenzenium picrate (DADCBP) has been successfully grown by solvent slow evaporation method. DADCBP crystallizes in a triclinic structure with the centrosymmetric space setup, P-1. The molecular structure of the grown crystal has been determined by NMR spectral analysis. The existence of discrete functional branches of the crystal has been identified by FTIR spectral study. The optical property of the title crystal has been measured by UV-Vis-NIR spectral analysis. PL spectra reveal the emission bands of the grown crystal. The thermal stability of the harvested crystal has been examined by the TG/DTA study. The dielectric constant and loss have been taken to locate the arrangement of charges in the grown crystal. The quantum chemical studies have been performed to analyze the HOMO/LUMO, molecular geometry, and mulliken atomic charge by B3LYP at the 6-311++G (d,p) level of theory. H···H, O···H, C···H, C···C various intermolecular interactions of hydrogen bonds in the DADCBP molecule have been visualized by the Hirshfeld surface analysis. The nonlinear optical (NLO) characteristics like nonlinear absorption coefficient (β), nonlinear refractive index (n2) and susceptibility (χ(3)) have been examined using the Z-scan technique.

The Effect of PH Value on Shear Thickening and Chemical Compound Effect Polishing Solution

When the traditional polishing method is used to process brittle materials such as lithium niobate, brittle failure is easy to occur, and many microcracks remain on the surface of the workpiece. Thus, the traditional method is not suitable for ultra-precision machining with higher surface roughness requirements. In this paper, a new type of high-performance polishing fluid with shear thickening and chemical compound effect was developed. The shear thickening effect was combined with the chemical effect, which was dedicated to the ultra-precision polishing of difficult-to-machine materials, such as optical crystals and semiconductors. The results show that the best polishing effect is achieved when the pH value is 9.5.

Synthesis and characterization of a new chalcone-based nonlinear optical crystal: BBC

A new chalcone-based nonlinear optical crystal BBC (C22H17BrO2) using long π-conjugated and halogen substituent, as a potential alternative to develop organic crystals, are reported. BBC was designed and synthesized by replacing benzyloxy and -Br groups on both sides of molecular framework. Flaky yellowish BBC single crystal with size of 5 × 5 × 1 mm3 was grown by solution evaporation method. BBC crystal crystallizes in the monoclinic system, Pc (NO. 7) space group, with noncentrosymmetric structure. In the BBC molecule, benzyl oxide acts as donor (D) and Br and carbonyl group act as acceptor (A), forming D - π - A - π - A structure with electron gradient. The introduction of Br group, which contributes to strong halogen bond formation, lead to the “head-to-tail” arrangement. Remarkably, BBC exhibits strong second harmonic generation (SHG) intensity (14 × KDP and 2.2 × Urea), wide transmission range (600-1600 nm, >60%), high optical energy gap (Eg=2.85 eV) and high thermal stability (Tm=106 °C). In addition, to investigate the relationships between the structure and physical properties, the electronic structure and optical properties of BBC crystal were theoretically calculated. This work not only provides a newly chalcone-based NLO crystal, but also presents a feasible molecular design approach by introducing long π-conjugated and halogen substituents.

All-optical method of generation of Phase Shift Keying data using optical pockels crystal

All-optical method of generation of Phase Shift Keying data using optical pockels crystal

Investigation on the synthesis, growth, thermal and optical behavior of creatininium borate single crystal: A potential candidate for nonlinear optical applications

In the this study, we focus on the growth of a metal-organic creatininium borate (CRB) single crystal for third-order nonlinear optical (NLO) applications. Optically transparent & wide optical band gap single crystals of CRB were successfully harvested by adopting a slow evaporation solution technique (SEST) at a constant 40[Formula: see text]C temperature. The structural identification and lattice parameters of the grown sample were determined by powder X-ray diffraction (PXRD) using Rietveld analysis by FullProf Suite software. The occurrence of vacancy/interstitial defects produced during growth was investigated by high-resolution X-ray diffraction (HRXRD) using omega scan arrangement. A single peak with lower full width half maxima (56.4 arc s) was obtained from the scan which suggests that there were no grain boundaries for the grown crystal. Surface morphology and its features such as concentration of dislocations and defect sites on the as-grown sample were scrutinized using the etching technique. The optical band gap and UV–vis cut-off were examined and found to be 5.39 eV and 230 nm, respectively. Photoluminescence characteristics of the crystal show an emission at 377 nm upon excitation with a wavelength of 336 nm. The presence of radiative and non-radiative transitions inside the crystal due to excitation upon 266 nm laser was identified using time-resolved photoluminescence. Thermal stability and decomposition temperature of the compound were obtained by thermo-gravimetric analysis (TGA) and differential scanning calorimetry (DSC). The third-order nonlinearity of the crystal was determined by Z-scan measurement technique with a femtosecond Ti-sapphire laser.

Nanohardness Measurements of CdSiP2 and ZnGeP2 Chalcopyrite-Type Nonlinear Optical Crystals

We study the nanohardness and Young’s modulus of randomly oriented CdSiP2 (CSP) and ZnGeP2 (ZGP) single crystals, grown via the horizontal Bridgman method. CSP and ZGP are the only two pnictide chalcopyrites widely used as nonlinear optical crystals in the mid-IR part of the spectrum. Nanoindentation is employed in the continuous stiffness mode (45 Hz, 2 nm) using a Berkovich tip. Nanohardness values of 9.9 ± 0.2 GPa (Knoop hardness of 905 kg/mm2) for CSP and 11.5 ± 0.1 GPa (993 kg/mm2) for ZGP are derived. For Young’s modulus, we obtain 136 ± 2 GPa (CSP) and 150 ± 2 GPa (ZGP). The trend of increasing hardness with bandgap and melting point of the isostructural CSP and ZGP, as deduced from previous measurements, is not confirmed. The results for ZGP are compared to 2GaP, its binary isoelectronic analog, and the values obtained, 11.0 ± 0.3 GPa for the nanohardness and 154 ± 2 GPa for Young’s modulus, indicate good matching within the accuracy limits.

The role of semiconductors in the future of optical fibers

Semiconductors-core optical fibers have gathered attention for light guidance in the infrared spectrum. Cladded with glasses, fibers can be the ideal medium to transfer the favorable bulk properties of semiconductors into the micro/nano scaled one-dimensional form. The integration of these fibers with optical circuits, lasers and photonic crystals offers a wide variety of applications. In this perspective, the role of semiconductors in the future of optical fibers and their integration with photonic crystal structures are analyzed. The past and present efforts of semiconductor-core fibers are briefly reviewed, and the potential future application areas benefited by semiconductors as fiber materials are discussed.

Crystal Growth, Characterization, and Properties of Nonlinear Optical Crystals of LixAg1-xGaSe2 for Mid-Infrared Applications.

LixAg1-xGaSe2 is a new series of solid solution crystals that has a large nonlinear optical (NLO) coefficient and laser-induced damage threshold (LIDT). It has great application prospects in mid-infrared laser frequency conversion. In this work, LixAg1-xGaSe2 (x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, and 1) crystals (Φ 16 mm × 40 mm) were grown by the improved Bridgeman method in a four-zone furnace. It is found that the LixAg1-xGaSe2 (x = 0.2-0.8) crystals keep the same tetragonal symmetry with AgGaSe2 and the melting and solidification temperature increase with the Li content. Because the as-grown crystals are almost opaque in the visible-NIR range, an annealing experiment is necessary. After annealing, the transmittance is improved significantly, which can meet the application requirements. The band gap is changed by annealing atmosphere; for instance, the band gap of Li0.6Ag0.4GaSe2 annealed in a LiGaSe2 powder atmosphere increases from 2.35 to 2.56 eV, while the band gap of LiGaSe2 annealed in vacuum decreases from 3.39 to 3.01 eV. Finally, the LixAg1-xGaSe2 shows an extreme SHG response, especially Li0.8Ag0.2GaSe2, which has about five times that of LiGaSe2, proving the promising NLO properties.

Light gap bullets in defocusing media with optical lattices

Searching for three-dimensional spatiotemporal solitons (also known as light/optical bullets) has recently attracted keen theoretical and experimental interests in nonlinear physics. Currently, optical lattices of diverse kinds have been introduced to the stabilization of light bullets, while the investigation for the light bullets of gap type – nonlinear localized modes within the finite gap of the underlying linear Bloch spectrum – is lacking. Herein, we address the formation and stabilization properties of such light gap bullets in periodic media with defocusing nonlinearity, theoretically and in numerical ways. The periodic media are based on two-dimensional periodic standing waves created in a coherent three-level atomic system which is driven to the regime of electromagnetically induced transparency, which in principle can also be replaced by photonic crystals in optics or optical lattices in ground-state ultracold atoms system. The temporal dispersion term is tuned to normal (positive) group velocity dispersion so that to launch the light gap bullets under self-repulsive nonlinearity; two types of such light gap bullets constructed as three-dimensional gap solitons and vortices with topological charge m=1 within the first finite gap are reported and found to be robustly stable in the existence domains. On account of the light bullets were previously limited to the semi-infinite gap of periodic media and continuous nonlinear physical systems, the light gap bullets reported here thus supplement the missing type of three-dimensional spatiotemporal localized modes in periodic media which exhibit finite band gaps.