A Lanthanum Ammonium Sulfate Double Salt with a Strong SHG Response and Wide Deep‐UV Transparency

Abstract

The targeted synthesis of deep-ultraviolet (deep-UV) nonlinear optical (NLO) materials, especially those with non-π-conjugated sulfates, has experienced considerable difficulties due to the need to reconcile the oft-competing requirements for deep-UV transparency and strong second-harmonic generation (SHG). We report herein the designed synthesis of the first rare-earth metal-based deep-UV sulfate La(NH 4 )-(SO 4 ) 2 by a double-salt strategy involving introduction of complementary cations, together with optical studies that reveal a short-wavelength deep-UV absorption edge (below 190 nm) and the strongest SHG response among deep-UV NLO sulfates (2.4 × KDP). Theoretical calculations and crystal structure analysis suggest that the excellent balance between SHG response and deep-UV transparency can be attributed to a synergistic interaction of the hetero-cations La 3 + and [NH 4 ] + , which optimize alignment of the [SO 4 ] tetrahedra and highly polarizable [LaO 8 ] polyhedra.

Cs2Bi2OSi2O7: A Promising Bismuth Silicate Nonlinear Optical Crystal with Face-Sharing BiO5 Polyhedra Exhibiting Strengthened Second Harmonic Generation Response and Birefringence

“…As presented in Figure a, the SHG signal of CBSO enhances along with the increasing particle sizes before it reaches the maximum value that implies phase-matching nature, as defined by Kurtz and Perry, and CBSO displays a strong SHG intensity of ∼3.5 × KDP in the particle size range of 180–212 μm (Figure b). Notably, the observed result of CBSO is comparable to that of the universally used practical crystal LBO (3 × KDP). , As deposited in Figure c, CBSO has an impressive UV cut-off edge of 279 nm and gives wide band gaps of 3.6 eV, which may be beneficial for reducing two-photon absorption, according to the previous studies. − The IR spectrum tests demonstrate that CBSO exhibits no obvious absorption in a broad range of 4000–1045 cm –1 (Figure d); thus, CBSO is transparent in a wide region over 3–5 μm based on the two-phonon approximation, which is favorable for mid-IR NLO applications Table S3 lists the absorption bands and assignments of CBSO. , …”

NaHSO4·H2O: A Promising Deep-Ultraviolet Nonlinear-Optical Bisulfate with Large Birefringence and a Second-Harmonic-Generation Effect

“…According to the formula in eq S1, the birefringence of the NaHSO 4 •H 2 O crystal can be determined as 0.042 at 546 nm. Notably, such a large birefringence is the largest among the DUV NLO sulfates to date, significantly larger than the recently reported DUV NLO sulfates, such as Li 2 SO 4 •H 2 O (0.023 at 1064 nm), 23 K 2 Zn 3 (SO 4 )(HSO 4 ) 2 F 4 (0.0126 at 546 nm), 24 La(NH 4 )(SO 4 ) 2 (0.03 at 1064 nm), 25 ] units is conducive to producing a stronger structural anisotropy. 27 Therefore, the excellent performance and rational arrangement of the [HSO 4 ] units together determine the greater birefringence.…”

Local Polarity-Induced Assembly of Second-Order Nonlinear Optical Materials

“…Non-π-conjugated (PO 4 ) 3– , (P 2 O 7 ) 4– , and (SO 4 ) 2– tetrahedra have recently been recognized as new sources of functional building units of second-order NLO materials. ,,− As compared to conventional planar π-conjugated anion units, these non-π-conjugated tetrahedral units are beneficial for larger energy bandgaps or wider optical transmittance windows because of the low electron energy of their σ bonds. However, owing to the absence of π orbitals intrinsic to strong optical anisotropy, that is, large hyperpolarizability and polarizability anisotropy, non-π-conjugated second-order NLO materials usually exhibit relatively weak SHG responses and small birefringence .…”