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)3]2PO3F, 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.