UV Solar-Blind-Region Phase-Matchable Optical Nonlinearity and Anisotropy in a π-Conjugated Cation-Containing Phosphate

Wide ultraviolet (UV) transparency, strong second-harmonic generation (SHG) response, and sufficient optical birefringence for phase-matching (PM) at short SHG wavelengths are vital for practical UV nonlinear optical (NLO) materials. However, simultaneously optimizing these properties is a major challenge, particularly for metal phosphates. Herein, we report a non-traditional pi-conjugated cation-based UV NLO phosphate [C(NH2)(3)](6)(PO4)(2).3 H2O (GPO) with a short UV cutoff edge. GPO is SHG active at 1064 nm (3.8 x KH2PO4 @ 1064 nm) and 532 nm (0.3 x beta-BaB2O4 @ 532 nm) and also possesses a significant birefringence (0.078 @ 546 nm) with a band gap >6.0 eV. The PM SHG capability of GPO can extend to 250 nm, indicating GPO is a promising UV solar-blind NLO material. Calculations and crystal structure analysis show that the rare coexistence of wide UV transparency, large SHG response, and optical anisotropy is due to the introduction of pi-conjugated cations [C(NH2)(3)](+) and their favorable arrangement with [PO4](3-) anions.

Automated summary

GPO is a non-traditional UV NLO phosphate material with wide UV transparency, strong SHG response, and sufficient optical birefringence, making it suitable for phase-matching at short SHG wavelengths. Due to the introduction of pi-conjugated cations and their favorable arrangement with anions, GPO shows promising potential as a UV solar-blind NLO material that simultaneously optimizes wide UV transparency, large SHG response, and optical anisotropy.