Nonlinear Optical Oxythiophosphate Approaching the Good Balance with Wide Ultraviolet Transparency, Strong Second Harmonic Effect, and Large Birefringence

Abstract

Ultraviolet (UV) transparency, second harmonic effect and optical birefringence are three vital but mutually restrictive factors in the application of UV nonlinear optical (NLO) materials. It is difficult for traditional phosphates to achieve a good balance among these factors. In this communication, we propose that the structural evolution of the NLO motif from traditional phosphate to oxythiophosphate would enhance the birefringence and second harmonic generation (SHG) effect while maintaining wide UV transparency, which is confirmed by first‐principles calculations and preliminary experimental measurements. Following this strategy, we predict that, compared with the well‐known NLO phosphate KH2PO4, the oxythiophosphate KH2PO3S exhibits better balance for the UV NLO performance, including wide UV transparency (UV cutoff down to 203 nm), strong SHG effect (ca. 0.9 pm V−1), and large birefringence (ca. 0.1 at 1 μm) with short phase‐matching SHG output wavelength (≈214 nm).

Mg2In3Si2P7: A Quaternary Diamond-like Phosphide Infrared Nonlinear Optical Material Derived from ZnGeP2

“…The results (Table S10) showed that the SHG coefficients and birefringence mainly originated from P 3– . Besides, among the three cations In 3+ exhibited the largest contribution, Si 4+ came second, and Mg 2+ had a negligible contribution, which indicated that the giant SHG response and large birefringence mainly arose from the synergy of [InP 4 ] and [SiP 4 ] tetrahedra. − …”

K3V2O3F4(IO3)3: a high-performance SHG crystal containing both five and six-coordinated V5+ cations

“…[4][5][6] Notably, SHG efficiency and birefringence are primarily related to the polarization and anisotropic properties of crystal structures. [7][8][9] The iodate anion is able to exhibit giant microscopic acentricity owing to the second-order Jahn-Teller (SOJT) distortion induced by the lone-pair electrons of I 5+ cation. [10][11][12] Accordingly, the designs and syntheses of novel metal iodates with aligned IO 3 groups have attracted tremendous commercial and academic interest.…”

Finding Short-Wavelength Birefringent Crystals with Large Optical Anisotropy Activated by π-Conjugated [C(NH2)3] Units

“…In addition, the large birefringence in BaTiS 3 originates from the quasi-1D infinite chain of [TiS 3 ] ∞ , which indicates that the reduction of spatial dimension can also be used to enlarge the polarization anisotropy . In recent years, more crystals with four-coordinated units, such as [BO x F 4– x ] ( x = 0–4), ,− , [PO 3 F], − [PO x S 4– x ] ( x = 0–4), and [SiO x N 4– x ] ( x = 0–4), , are reported to have enlarged birefringence when compared with their pure oxidized tetrahedra. This can be well-explained by the positive roles of F/N/S atoms on reducing the symmetry of original units to enhance the optical polarization anisotropy and birefringence. ,− Even though, to be as a birefringent material, the π-conjugated system has more competitiveness when compared with non-π-conjugated ones. ,,− ,− …”