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Carbonates deserve to be pursued in the exploration of candidate systems for birefringent crystalline materials. Recently, we successfully obtained a novel example of a mixed-metal carbonate, Cs2Pb(CO3)2, using a high-temperature solution method in a closed system. Structural analysis shows that the rare Pb-C-O one-dimensional chain structure is formed by interconnecting the fundamental building blocks of PbC2O8. Detailed structural analyses and comparisons suggest a non-coplanar arrangement of CO3 due to the highly distorted polyhedra formed by Pb2+. Theoretical calculations indicate that Cs2Pb(CO3)2 exhibits an average calculated birefringence of 0.037 @ 1.64 nm, which is consistent with the conclusions deduced from the structure. The source of the properties is further elucidated through real-space atom cutting. This work provides a good reference idea for designing and synthesizing new carbonate optical crystal materials. [ABSTRACT FROM AUTHOR]

Two new family members of mixed alkali-earth metal phosphate and aluminophosphate CaMg(P4O12) and Cs3Al4(PO4)5 were prepared from a phosphate system using a high-temperature solution method. The structural analysis results show that two compounds crystallize in the monoclinic space group C2/c and P21/n and feature a three-dimensional (3D) network. The 3D structure of CaMg(P4O12) consists of [CaO6], [MgO6] octahedra and [P4O12] rings, in which the [MgO6] and [P4O12] rings link to form a 3D structure and Ca2+ cations are filled within the structure. Interestingly, for compound Cs3Al4(PO4)5, its structure features 4, 8, and 12-ring channels with [Al2O4O4P2O4], [Al4O8O8P4O8] and [Al6O12O12P6O12] units as BBUs, respectively; the Cs+ cations are located in the cavities. Furthermore, IR spectral analysis and thermal properties are discussed. UV-vis-NIR diffuse reflectance spectroscopy data show that the UV cutoff edges of CaMg(P4O12) are below 200 nm. Remarkably, in order to determine optical properties and the structure-properties relationship, theoretical calculations were adopted. Electronic structure calculations demonstrate that CaMg(P4O12) has an indirect band gap with the value of 5.86 eV, and Cs3Al4(PO4)5 has a direct band gap of 5.21 eV. [ABSTRACT FROM AUTHOR]

Rare-earth phosphates were thought to be good candidates as ultraviolet/deep ultraviolet optical materials due to their relatively large bandgap and optical properties. In this paper, the authors screened out a family of XPO4 (X = Sc, Y, La, and Lu) compounds with an enhanced bandgap (HSE06 bandgap ≥ 7.61 eV) and birefringence (0.0934–0.2003@1064 nm) using first-principles calculations. The origin of enhanced optical properties was investigated using projected density of states, distortion indices, and Born effective charges. The results show that the PO4 anionic groups and X–O polyhedra give the main contribution in determining the optical properties, and the PO4 anionic groups give more contribution than other functional basic units. The spin–orbit interaction was also investigated. Similar band structures were found after spin–orbit coupling (SOC) was considered, and slightly enhanced birefringence was found when SOC was applied to these rare-earth phosphates. [ABSTRACT FROM AUTHOR]

Introducing post-transition metal cations is an excellent strategy for enhancing optical properties. This paper focuses on four isomers, namely the X2PO4I (X = Pb, Sn, Ba, and Sr) series. For the first time, the paper's attention is paid to the changes in electronic structure, as well as refractive indices and birefringence, with and without the inclusion of spin–orbit effects in this series. The first-principles results show that spin–orbit effects of the 5p and 6p states found in these compounds lead to splitting of the bands, narrowing of the band gap, enhancement of the lone-pair stereochemistry, and enhancement of the refractive indices and birefringence. Moreover, a comparison of the lone-pair electron phosphates, X2PO4I (X = Pb and Sn), and the isomeric alkaline earth metal phosphates, X2PO4I (X = Ba and Sr), reveals that changes in the band structure have a greater effect on the enhancement of the birefringence than the slight enhancement of the lone-pair stereochemical activity. This study has important implications for a deeper understanding of the optical properties of crystals and the design of novel optical materials. [ABSTRACT FROM AUTHOR]

Two-dimensional transition-metal dichalcogenides, specifically MTe2 (M = V and Ta), have recently inspired significant interest due to their unique electronic properties. However, their ultrafast nonlinear optical properties have not been extensively studied for use in ultrafast photonics applications. In this study, MTe2 (M = V and Ta) nanosheets were prepared using the liquid-phase exfoliation technique, and their bandgaps were calculated using density functional theory. The results show that both materials exhibit zero bandgaps, indicating that they are suitable for broadband photonic applications. The nonlinear absorptions of VTe2 and TaTe2 were characterized at 1.5 μm, with saturation intensities of 0.61 MW cm−2 and 1.36 MW cm−2, and modulation depths of 2.30% and 2.55%, respectively. By using the two fabricated materials as saturable absorbers, highly-stable passively mode-locked Er-doped fiber lasers were achieved for the first time, with pulse durations of 494 and 773 fs. Our experimental findings not only demonstrate the potential of MTe2 (M = V and Ta) in ultrafast photonics applications, but also advance photonic and optoelectronic applications. [ABSTRACT FROM AUTHOR]

Enhancing anisotropy through the controlled arrangement of anionic groups is essential for improving the nonlinear optical (NLO) performance of non‐π‐conjugated NLO materials. In this study, we present the successful synthesis of the first examples of mixed alkali metal‐alkaline earth metal sulfamate materials, including noncentrosymmetric Cs2Mg(NH2SO3)4 ⋅ 4H2O (1), as well as centrosymmetric K2Ca(NH2SO3)4 (2) and Rb2Ca(NH2SO3)4 (3). All three compounds feature promising deep ultraviolet cut‐off edges, notably 1 with a cut‐off edge below 180 nm. The synergy of Cs+ and Mg2+ cations in 1 facilitated the successful alignment of polar [NH2SO3] tetrahedra in a uniform orientation. Remarkably, 1 stands as the sole instance among reported sulfamate compounds with a co‐parallel anionic arrangement, yielding a very large dipole moment compared to other non‐π‐conjugated NLO materials. Moreover, the substantial dipole moment of 1 yields an enhanced second harmonic generation response, approximately 2.3 times that of KH2PO4, and a large birefringence of 0.054 at 546.1 nm. The approach of regulating the arrangement of anionic groups using aliovalent cations holds promise for advancing the exploration of non‐π‐conjugated NLO materials. [ABSTRACT FROM AUTHOR]