High-performance NLO Materials Research Articles

Unveiling the Twisted Aromatic Donor Effect on the Nonlinear Response of D-π-A Type Malononitrile-Derived Chromophores.

This study presents the design, synthesis, and comprehensive characterization of a novel series of D-π-A type malononitrile-derived chromophores, BTC-1-BTC-4. Combining various spectroscopic techniques, nonlinear Z-scan measurements, and quantum chemical calculations, we revealed the intricate relationship between nonlinear optical properties and the interplay of molecular structure, intramolecular charge transfer (ICT), and dipole moments (μ). Our experimental and computational findings corroborate that the polarization degree in the ground state, the charge separation in the excited state and twisted intramolecular charge transfer (TICT) collectively dictate the nonlinear optical properties of the compounds. Notably, BTC-1 exhibits an exceptional nonlinear absorption coefficient β value (2×10-8 m W-1), attributed to its optimized charge transfer efficiency and pronounced degree of charge separation. Our findings provide actionable insights for the rational design of high-performance organic Nonlinear optics (NLO) materials with potential applications in advanced photonic devices.

DFT investigation of M2F superalkali doped dodecafluorophenylene (C13H10F12) derivatives with remarkable static and dynamic NLO response

Herein, based on density functional theory (DFT) simulations, the static and dynamic hyperpolarizabilities of the superalkalides based on Janus molecules have been explored. The designed superalkalides M2F(F)-DDFP-M2F(H) contain Janus based Dodecafluorophenylene (DDFP) molecule doped with superalkalis on both sides acting as both electron acceptors and donors. Thermodynamic stabilities are evident from the negative values of interaction energies, which are observed in the range of −2.96 eV to −3.63 eV. The maximum interaction energy (Eint) obtained is −3.63 eV for Li2F(F)-DDFP-Li2F(H) complex. The NBO (natural bond orbital) and FMO (frontier molecular orbital) analyses confirm the true superalkalide nature of the designed complexes. FMO analysis further reveals the reduction in energy gap E(H-L) from 10.43 eV (for bare DDFP) to 3.17 eV for the designed superalkalis. Furthermore, NLO response of the studied complexes reveals that the maximum values of polarizability (617 au) and hyperpolarizability are seen for Na2F(F)-DDFP-K2F(H) (4.25 × 104 au) complex, which confirms the remarkable NLO response of newly designed superalkalides. Moreover, frequency dependent analysis indicates that the maximum values of simple harmonic generation (SHG), electro-optical pockel effect (EOPE) and hyper Rayleigh scattering are 7.79 × 106, 2.75 × 106 and 4.45 × 106 au, respectively. The EOKE and EFISHG values are 6.79 × 107 and 7.68 × 1010 at 1339 nm suggesting significant increase in the NLO response of the reported complexes. These results manifest that our designed complexes might provide new paths towards the exceptionally high performance NLO materials. Moreover, we expect that the present work will provide guidance for designing and synthesis of superalkali based NLO materials in future.

Infrared nonlinear optical materials with multiple strongly ionic cations

Infrared nonlinear optical (IR-NLO) crystals with excellent properties are in extensive demand due to their important role in IR laser technology. Currently, it remains a great challenge to obtain IR-NLO materials with both high second harmonic generation (SHG) response and large laser-induced damage thresholds (LIDTs). Some structural design strategies such as ‘structural/functional regions’ have been adopted to develop new high-performance NLO materials. The covalent structural region producing SHG signals has been extensively investigated, whereas the hard cations (alkali, alkaline-earth, and rare-earth metal ions) which are responsible for improving LIDTs, have been relatively neglected. Utilizing the concept of structural/functional regions, we focus on the relation between structural regions and SHG properties in chalcogenides. Combining different kinds of hard cations can change the dimension of structures and affect the stacking of NLO-active groups. Introducing more hard cations and constructing more complex ion regions help to increase the laser damage threshold. Based on the mentioned structural strategies, guidance will be provided for developing high-performance multiple-cation materials for IR NLO applications.

Theoretical Investigation of Structural, Electronic and Optical Properties of Cs3MoO4(HCO3) with NLO Active Functional Units

AbstractEmploying functional building units with microscopic second‐order NLO response has been proposed to explore high performance NLO materials. Herein, structural, electronic and optical properties of non‐centrosymmetric molybdenyl carbonate Cs3MoO4(HCO3) with NLO active functional units have been examined based on density functional theory. Theoretical results are consistent with experimentally mentioned data, confirming the reliable method. Detailed geometric structure, electronic attributes, linear optical properties, and nonlinear optical properties of Cs3MoO4(HCO3) are provided. Analysis of structures, compositions of bands and plots of charge density suggest that asymmetric functional building units [MoO4] and [HCO3] exhibit varying degrees of second‐order Jahn‐Teller distortions, and therefore have a significant impact on the electronic structure and optical properties of Cs3MoO4(HCO3). Maximum absolute value of SHG coefficients at 1064 nm is 0.671 pm/V for d15, which is nearly twice as much as that of KDP. Further researches are needed in future to validate and enhance optical anisotropy characteristic of Cs3MoO4(HCO3) for satisfying the phase matching conditions. Analysis results indicate that microscopic origins of SHG response in Cs3MoO4(HCO3) are complicated, such as geometric environment, induced polar asymmetric functional building units, and electronic properties. Continuous research on structure‐property relationship of NLO materials is needed for exploring more competitive NLO materials.

Secondary-Bond-Driven Construction of a Polar Material Exhibiting Strong Broad-Spectrum Second-Harmonic Generation and Large Birefringence.

Considerable effort has been invested in the development of non-centrosymmetric (NCS) inorganic solids for ferroelectricity-, piezoelectricity- and, particularly, optical nonlinearity-related applications. While great progress has been made, a persistent problem is the difficulty in constructing NCS materials, which probably stems from non-directionality and unsaturation of the ionic bonds between metal counter-cations and covalent anionic modules. We report herein a secondary-bond-driven approach that circumvents the cancellation of dipole moments between adjacent anionic modules that has plagued second-harmonic generation (SHG) material design, and which thereby affords a polar structure with strong SHG properties. The resultant first NCS counter-cation-free iodate, VO2 (H2 O)(IO3 ) (VIO), a new class of iodate, crystallizes in a polar lattice with VO2 (H2 O)(IO3 )] zigzag chains connected by weak hydrogen bonds and intermolecular forces. VIO exhibits very large SHG responses (18 × KH2 PO4 @ 1200 nm, 1.5 × KTiOPO4 @ 2100 nm) and sufficient birefringence (0.184 @ 546 nm). Calculations and crystal structure analysis attribute the large SHG responses to consistent polarization orientations of the VO2 (H2 O)(IO3 )] chains controlled by secondary bonds. This study highlights the advantages of manipulating the secondary bonds in inorganic solids to control NCS structure and optical nonlinearity, affording a new perspective in the development of high-performance NLO materials.

Superalkali-alkaline earthide ion pairs of δ+(AM-HMHC)-AM'δ- (AM = Li, Na and K; AM' = Be, Mg and Ca) possessing large NLO responses and excellent electronic stabilities and alkalide characteristics: a DFT study.

To identify superalkali-alkaline earthide ion pairs, it's theoretically shown that, as a novel class of excess electron superalkali compounds, both chair and boat forms of (AM-HMHC)-AM' (AM = Li, Na, and K; AM' = Be, Mg, and Ca; HMHC = 1,4,7,10,13,16-hexamethyl-1,4,7,10,13,16-hexaazacyclooctadecane) are good candidates. An attractive superalkali-alkaline earthide ion pair in δ+(AM-HMHC)-AM'δ- is firstly exhibited, which possesses alkaline-earthide characteristics and nonlinear optical response superior to similar M+(calix[4]pyrrole)M'- (M = Li, Na, and K; M' = Be, Mg, and Ca) with high stability. The electronic and vibrational second order hyperpolarizabilities and the frequency-dependent first hyperpolarizabilities of δ+(AM-HMHC)-AM'δ- are presented. For each pair of (AM-HMHC)-AM', the boat conformation is preferred to its chair one in the case of Hyper-Rayleigh scattering response (βHRS). These alkaline earthides suggest prominently high βHRS up to 2.59 × 104 a.u. (boat forms of δ+(Na-HMHC)-Caδ-). We expect that this work will inspire the preparation and characterization of these new alkaline earthides as high-performance NLO materials.

Exohedrally and endohedrally doped 15-crown-5 (a crown ether) surface by metals for potential applications as high-performance NLO materials

Exohedrally and endohedrally doped 15-crown-5 (a crown ether) surface by metals for potential applications as high-performance NLO materials

Alkali metals doping into open-cage fullerenes: Novel alkalides (M+@C50N5H5)Mʹ− with large nonlinear optical responses

Based on open-cage fullerenes C50N5H5, a novel type of compounds (M+@C50N5H5)Mʹ− (M = Li, Na; Mʹ = Li, Na and K) was designed and studied. Firstly, their alkalides’ properties are confirmed by their FMO and NPA charges analysis. In particular, the proposed alkalides exhibited considerable first hyperpolarizability (β0) up to 1.91 × 105 a.u., which indicated that they could be regarded as high-performance novel NLO molecules. These alkalides will pave the way for further exploration of electronic-stable, high-performance NLO materials.

Oxychalcogenides: A Promising Class of Materials for Nonlinear Optical Crystals with Mixed-Anion Groups.

Infrared nonlinear optical (IR NLO) materials are of great significance in the development of IR laser technology. But rationally designing high-performance IR NLO materials remains a huge challenge due to the conflict between the necessary properties required for NLO materials. Notably, oxychalcogenides with mixed-anion groups have drawn extensive interest as a family of important IR NLO candidates because they integrate the property advantages of oxides and chalcogenides by chemical substitution engineering. In this review, we provide a survey of reported oxychalcogenides and aim to present the development of NLO oxychalcogenides from the perspective of rational design of their structural chemistry. Furthermore, we focus on the relationships between partial substitution and structural symmetry as well as optical properties. These provide some helpful guidance for the further exploration and design of novel oxychalcogenide materials with excellent NLO performance in the future.

Theoretical study of [36]adamanzane (36Adz) based alkalides with remarkable non-linear optical properties

Herein, a series of 36Adamanzane (stable C–N bond) based alkalides possessing alkaline Earth metal cation complexed by the 36Adz cage has been designed and studied with theoretical tools. All suggested complexes are within the range of effective NLO materials such as red-shifted λ max (1080–1241 nm), narrowed Eg (1.74 to 2.31 eV), lowered Eopt (0.9945–1.1485 eV), enhanced (5.3873–6.2544 au), ameliorated (454.20–1400.34 au) and (801301.48–819800.06 au) as compared to pure 36Adz (Eg = 10.2 eV, λ max = 179 nm, Eopt = 6.9217, = 241.64 and = 0.02 au). All of the aimed complexes have substantially large as well as values. NBO charges investigations reveal that one of the s-electrons has migrated from the inside metal atom to the outer one, resulting in not only alkalide characteristics but also significant NLO responses for the targeted compounds. This research is useful in the development of new types of excess electron compounds. The findings presented in this study may have implications for future research on high-performance NLO materials, as well as give important references for future research on various alkalides including non-alkali cations.

Anisotropic structure building unit involving diverse chemical bonds: a new opportunity for high-performance second-order NLO materials.

We define the anisotropic structure building unit that encompasses diverse chemical bonds (ABUCB). The ABUCB is highly likely to cause anisotropy in both crystallographic structure and spatial electron distribution, ultimately resulting in enhanced macroscopic optical anisotropy. Accordingly, the (PO3F)2- or (SO3F)- tetrahedron involving the unique P-F or S-F bond serves as such an ABUCB. The distinct chemical bond effectively alters the microscopic nature of the structure building unit, such as polarizability anisotropy, hyperpolarizability, and geometry distortion; this consequently changes the macroscopic second-order nonlinear optical (2nd-NLO) properties of the materials. In this review, we summarize both typical and newly emerged compounds containing ABUCBs. These compounds encompass approximately 90 examples representing six distinct categories, including phosphates, borates, sulfates, silicates, chalcogenides and oxyhalides. Furthermore, we demonstrate that the presence of ABUCBs in DUV/UV NLO compounds contributes to an increase in birefringence and retention of a large band gap, facilitating phase matching in high-energy short-wavelength spectral ranges. On the other hand, the inclusion of ABUCBs in IR NLO compounds offers a feasible method for increasing the band gap and consequently enhancing the larger laser-induced damage threshold. This review consolidates various trial-and-error explorations and presents a novel strategy for designing 2nd-NLO compounds, potentially offering an opportunity for the development of high-performance 2nd-NLO materials.

Exohedrally and endohedrally doped calix-4-pyrrole surface by alkali and alkaline earth metals for potential applications as high-performance NLO materials

Exohedrally and endohedrally doped calix-4-pyrrole surface by alkali and alkaline earth metals for potential applications as high-performance NLO materials

The Antiperovskite-Type Oxychalcogenides Ae3 Q[GeOQ3 ] (Ae = Ba, Sr; Q = S, Se) with Large Second Harmonic Generation Responses and Wide Band Gaps.

Oxychalcogenides capable of exhibiting excellent balance among large second-harmonic generation (SHG) response, wide band gap (Eg ), and suitable birefringence (Δn) are ideal materials class for infrared nonlinear optical (IR NLO) crystals. However, rationally designing a new high-performance oxychalcogenide IR NLO crystal still faces a huge challenge because it requires the optimal orientations of the heteroanionic groups in oxychalcogenide. Herein, a series of antiperovskite-type oxychalcogenides, Ae3 Q[GeOQ3 ] (Ae = Ba, Sr; Q = S, Se), which were synthesized by employing the antiperovskite-type Ba3 S[GeS4 ] as the structure template. Their structures feature novel three-dimensinoal frameworks constructed by distorted [QAe6 ] octahedra, which are further filled by [GeOQ3 ] tetrahedra to form antiperovskite-type structures. Based on the unique antiperovskite-type structures, the favorable alignment of the polarizable [GeOQ3 ] tetrahedra and distorted [QAe6 ] octahedra have been achieved. These contribute the ideal combination of large SHG response (0.7-1.5 times that of AgGaS2 ), wide Eg (3.52-4.10eV), and appropriate Δn (0.017-0.035) in Ae3 Q[GeOQ3 ]. Theoretical calculations and crystal structure analyses revealed that the strong SHG and wide Eg could be attributed to the polarizable [GeOQ3 ] tetrahedra and distorted [QAe6 ] octahedra. This research provides a new exemplification for the design of high-performance IR NLO materials.

Theoretical study of 36Adz based alkaline earthides M+(36Adz)M− (M+ = Li & Na; M− = Be, Mg & Ca) with remarkable nonlinear optical response

The 36Adz complexant has been used to design and investigate another group of alkaline earthides, M+(36Adz)M−. Here, M+ represents the alkali metals i.e., Li & Na while M− represents alkaline earth metals i.e., Be, Mg & Ca. Basic pattern of arrangement of atoms in alkaline earthides includes the insertion of the alkali metal at the middle of hollow 36Adz cage and the space outside the cage is occupied by the alkaline earth metal. Natural bond orbitals are scrutinized, and calculation results show the alkaline earth metals as anions (negative charges on them). Highest occupied molecular orbitals are also analysed and the results of this analysis show that highest occupied molecular orbitals are present on alkaline earth metals. Both these characteristics confirm that the designed compounds are alkaline earthides. The same characteristic i.e., locale of excess electron, is further corroborated by the partial density of states spectra of the compounds. Moreover, extraordinarily higher first hyperpolarizabilities are shown by these compounds, the highest βo being shown (equal to 5.1 × 108 au) by Li+(36Adz)Mg−. These inordinately higher values of hyperpolarizability are ascribed to the distinctive feature of these compounds i.e., alkaline earth metals incorporate excess electron/bear negative charge. Furthermore, these complexes show very low transition energies (ΔE) and vertical ionization energy (VIE) values, ranging from 0.30 to 2.57 eV and 2.24 eV–2.51 eV, respectively. Such lower ΔE and VIE justify their larger values of hyperpolarizabilities. These results reveal that the alkaline earthides are a useful entry for high-performance NLO materials.

Assessment of alkali and alkaline earth metals doped cubanes as high-performance nonlinear optical materials by first-principles study

Novel organic materials have played a tremendous role in developing high-performance nonlinear optical materials. Herein, the geometric, electronic and nonlinear optical properties of designed alkali (Li, Na, and K) and alkaline earth metals (Be, Mg, and Ca) doped cubane (C 8 H 8 ) complexes have been explored by using density functional theory. Excess electrons generated by doping alkali/alkaline earth metals have significantly enhanced the NLO properties by reducing the crucial excitation energy of the cubane. The HOMO–LUMO energy gap of doped complexes is reduced up to 4.43 eV. It is revealed that the reduction in the HOMO–LUMO energy gap results from the development of the new highest occupied molecular orbital, which is confirmed by the density of state (DOS) analysis. The NBO analysis is carried out to confirm the charge transfer between metal atoms and the cubane ring. Further, the NCI and QTAIM analyses confirmed the nature of intramolecular interaction. The remarkable first hyperpolarizability ( β o ) of 3.01 × 10 4 au is observed for K@Cubane. Moreover, frequency dependent first hyperpolarizability ( β ( ω )), second harmonic generation β (-2 ω ; ω , ω ), electro-optic Pockel's effect β (- ω ; ω ,0), hyper-Rayleigh scattering coefficient ( β HRS ), second hyperpolarizability ( γ ( ω )), electric field-induced second harmonic generation γ (-2 ω ; ω , ω ,0) electro-optic Kerr effect γ (- ω ; ω ,0,0), and nonlinear refractive indices ( n 2 ) were also studied. The highest dc-Kerr (2.69 × 10 10 au ) and EFISHG (3.69 × 10 9 au ) values observed for K@Cubane along with large n 2 (1.73 × 10 −9 au ) justify the large NLO response. These intriguing outcomes will be advantageous for promoting the possible utilization of designed complexes in the field of high-performance NLO materials. • Alkali and alkaline earth metals doped cubane complexes have been investigated theoretically for better NLO response. • NBO analysis indicates the intermolecular charge transfer while NCI and QTAIM analyses validate non-covalent interactions. • All the doped complexes have deep ultraviolet transparency (≤200 nm). • First hyperpolarizability ( β o ) of doped cubane complexes have been enhanced to 3.01 × 10 4 au. • Hyper-Rayleigh scattering (upto 2.23×10 4 au ) and nonlinear refractive index (upto 1.15×10 −5 au ) reflect high NLO response.

Constructing a simple Cone–Chain motif to significantly enhance the first hyperpolarizability of horn-shaped carbon nanocones

According to the density functional theory (DFT) calculations, the first hyperpolarizabilities of the carbon nanocone (CNC)–based systems in a D–π–A framework can be prominently improved by constructing the mixed π-conjugated bridge. The hybrid π-conjugated bridge is constructed by modifying the bottom edge of CNC with –(CH CH) x –NH 2 /NO 2 chain. By connecting the –(CH CH) x –NH 2 chain with electron-donating characteristic, the first hyperpolarizabilities of these cone-chain systems can be enhanced more availably, and the substitution position can also play an important role in determining the β 0 value. The TDDFT calculations show that building the simple cone-chain motif can effectively improve the degree of charge transfer and reduce the transition energy, thus leading to a considerably large first hyperpolarizability, which is much larger than that of the corresponding directly NH 2 -decorated CNC system with the same conjugated length. Especially, the first hyperpolarizabilities of these cone-chain motifs (CNC–(CH CH) x –NH 2 ) can increase dramatically with the extension of –(CH CH) x –NH 2 chain. Furthermore, in view of the unique horn-shaped structure of CNC, another –(CH CH) x –NH 2 chain is added at the bottom edge for double-substitution, and it can further augment the first hyperpolarizability compared with the single-substitution. In addition, the length ratio of cone to chain in the mixed π-conjugate bridge can also have a crucial effect on the β 0 value of these cone-chain motifs. Using the –(CH CH) x –NH 2 with a comparable conjugated size to modify the bottom edge of cone can be an effective strategy for achieving the remarkable NLO response in the CNC-based system with D–π–A framework. These fascinating findings are advantageous for the design of new high-performance NLO materials based on CNCs. Constructing a simple cone–chain motif can be considered as a new and effective strategy to significantly increase the first hyperpolarizability of carbon nanocones (CNCs), which can be mainly attributed to the fact that when linking the π-conjugated –(CH CH) x –NH 2 /NO 2 chain with electron-donating/withdrawing characteristic, the abundant π electrons of CNCs can be well directed to result in the more effective charge transfer, just like inserting a straw into a glass of water, it allows the water to flow out more directionally. • Constructing a simple cone–chain motif can significantly increase the first hyperpolarizability of carbon nanocones (CNCs). • The β 0 value of CNC can be enhanced more effectively by linking electron-donating -CH=CH–NH 2 chain. • When elongating the chain length, a monotonous increasing trend can be observed for the β 0 value. • The double-chain substitution of –(CH=CH) x –NH 2 can further enhance the β 0 value of CNC system. • The β 0 value of CNC l –(CH=CH) x –NH 2 can be adjusted effectively by changing the length ratio of cone to chain.

DFT study of alkali and alkaline earth metal-doped benzocryptand with remarkable NLO properties.

Strategies for designing remarkable nonlinear optical materials using excess electron compounds are well recognized in literature to enhance the applications of these compounds in nonlinear optics. In this study, density functional theory simulations are performed to study alkali and alkaline earth metal-doped benzocryptand using the B3LYP/6-31G+(d, p) level of theory. Vertical ionization energies (VIEs), reactivity parameters, interaction energies, and binding energies exposed the thermodynamic stability of these complexes. FMO analysis revealed that HOMO is located on alkali metals having polarized electrons, which are easy to excite. The doping strategy enhanced the charge transfer with low bandgap energy in the range of 0.68–2.23 eV, which is lower than that of the surface BC (5.50 eV). Also, the lower transition energies and higher oscillator strength indicate that these complexes exhibit excellent electronic and optical properties. Non-covalent interaction analysis suggested the presence of van der Waals interactions between dopants and surface. IR analysis provided information about the frequencies of stretching vibrations present in the complexes due to different bonds. UV-vis analysis revealed that all the newly designed excess electron complexes are transparent in the UV region and possessed maximum absorption in the visible and NIR region, ranging from 753.6 to 2150 nm, which is higher than the surface (244 nm). Thus, these complexes have a potential for high-performance NLO materials in the applications of optics. Natural bond orbital analysis (NBO), transition density matrix (TDM), electron density difference map (EDDM), and density of state (DOS) analyses were also performed to study the charge transfer properties. Moreover, these complexes possessed remarkable optoelectronic properties due to a significant increase in the isotropic linear polarizability (αiso) in the range of 629.59–1423.23 au. Further, these systems demonstrated an extraordinary large total first hyperpolarizability (βtl) in the range of 3695.55–910 706.43 au. The rationalization of hyperpolarizability by the two-level model reflected a noteworthy increase in βtl because of low transition energies (ΔE) and high transition dipole moment (Δμ). Thus, our results showed that alkali and alkaline earth metal-doped BC might be a competitor for efficient nonlinear optical properties with practical applications in the area of optoelectronics.

Covalent-linked porphyrin-based polymer/multi-walled carbon nanotube nanohybrids: Synthesis and enhanced nonlinear optical performance

In this paper, a series of novel porphyrin-based polymers named poly(6-(5'-(4′-phenoxyl)-10′,15′,20′-triphenylporphyrin) methacrylate)n with different molecular weights and functional alkyne end-groups (PPorx-C≡CH) were successfully synthesized through reversible addition-fragmentation chain transfer (RAFT) polymerization. Furthermore, the corresponding multi-walled carbon nanotube (MWCNT) nanohybrids PPorx-MWCNTs were prepared by reacting PPorx-C≡CH with MWCNT-N3 through click reaction. PPorx-MWCNT exhibited obvious fluorescence quenching at 652 and 725 nm compared to PPorx-C≡CH, demonstrating the photo-induced electron transfer (PET) process between PPorx and MWCNT, which was proved by photo-electrochemical experiments. After covalent-linked with MWCNT, PPorx-MWCNT show an enhanced NLO performance (the third order optical susceptibility (Im[χ(3)]) = 4.93 × 10−11 esu) compared to PPorx-C≡CH in N,N-dimethylformamide (DMF) solution, causing by the PET process. In order to enhance the practicality of PPorx-MWCNT, the PPorx-MWCNT/polymethyl methacrylate (PPorx-MWCNT/PMMA) composites were prepared. Among them, PPor3-MWCNT/PMMA showed the best NLO performance (Im[χ(3)] = 5.58 × 10−11), with a limiting threshold of 0.98 J/cm2. Compared with methyl methacrylate (MMA) system, the weaker aggregation effect in PMMA matrix contributes to enhance the NLO properties of PPorx-MWCNT. Our study has opened a new path for the development of high performance NLO materials for practical applications.

Turning diamondoids into nonlinear optical materials by alkali metal Substitution: A DFT investigation

Electronic properties, absorption spectra and nonlinear optical properties of alkali metal substituted diamantanes are presented. A significant reduction in HOMO-LUMO gap has been observed by alkali metal substitution. K@CHa has the lowest H-L gap of 1.64 eV as compared to 8.88 eV for pristine diamantane. A remarkable increase in the first hyperpolarizability (βo) has been observed due to the substitution of alkali metals. Among these structures, K substituted complexes show the largest first hyperpolarizability (25526–36328 a.u). This significant increase in the first hyperpolarizability (βo) is attributed to low crucial transition energy (ΔE). K@CHa has the lowest ΔE value (2.06 eV) which results in the highest βo value (36328 a.u.) for K@CHa. Furthermore, frequency-dependent hyperpolarizability calculations have been carried out using 1906 nm and 1340 nm frequencies for commonly used lasers. The values of dynamic hyperpolarizabilities are greater than those of static ones for the majority of the substituted systems. This suggests the application of the proposed complexes under different frequencies of incident radiations. The substitution of alkali metals leads to the shift in absorption from ultraviolet to the visible region. Bathochromic shifts in the absorption spectra are observed with an increase in the size of alkali metal atom (λmax = 600 nm for K@CHa). This study provides an efficient approach to design high-performance NLO materials having extensive applications in the field of electronics and optoelectronics.

Prediction of Novel van der Waals Boron Oxides with Superior Deep-Ultraviolet Nonlinear Optical Performance.

Deep-ultraviolet nonlinear optical (DUV NLO) materials are attracting increasing attention because of their structural diversity and complexity. Using the two-dimensional (2D) crystal structure prediction method combined with the first-principles calculations, here we propose layered 18-membered-ring (18MR) boron oxide B2 O3 polymorphs as high-performance NLO materials. 18MR-B2 O3 with the AA and AB stackings are potential DUV NLO materials. The superior performing 18MR-B2 O3 AB has an unprecedentedly high second harmonic generation coefficient of 1.63 pm V-1 , the largest among the DUV NLO materials, three times larger than that of the advanced DUV NLO material KBe2 BO3 F2 and comparable to that of β-BaB2 O4 . Its unusually large birefringence of 0.196 at 400 nm guarantees the phase-matching wavelength λPM to reach this material's extreme absorption edge of ≈154 nm.