Monofluorophosphates: A New Source of Deep-Ultraviolet Nonlinear Optical Materials

Deep-ultraviolet (DUV) nonlinear optical (NLO) materials that have attracted considerable renewed interest are in great demand by the relevant industries, but there is a severe shortage of these materials. The existence of such a dilemma may be attributed to the extremely rigorous prerequisite for such materials, including a very wide energy gap (>6.2 eV), which can be met by only a few borates, phosphates, and carbonates; among them, only one, KBe2BO3F2 (KBBF), is practically usable. Herein, we theoretically identify PO3F2– as a novel DUV NLO building unit based on first-principles studies. In addition, we thoroughly survey more than 100 known monofluorophosphates and identify three of them, (NH4)2PO3F, C(NH2)32PO3F, and NaNH4PO3F·H2O, as promising DUV NLO candidates. To confirm our prediction, we experimentally synthesize all of them. Interestingly, these compounds exhibit remarkably strong second harmonic generations 0.9–1.1 × KH2PO4 (KDP) at 1064 nm and 0.2–0.3 × β-Ba2B2O4 (BBO) at 532 nm and high damage thresholds (2.3–3.1 × KDP at 1064 nm). Is it significant that this study offers a new functional building unit, PO3F, which opens a new avenue for designing and identifying DUV NLO materials, and thus, new monofluorophosphates showing better performance are highly anticipated.