In short, 2D vdW NLO crystal NbOCl₂ is experimentally discovered with unprecedented second-order optical nonlinearity and significant SPDC functionality, which would not only provide an ideal candidate for CMOS-integrated SPDC quantum light source but also open a new plat-form for low-dimensional quantum physics in 2D layered systems. Moreover, by optimizing pump conditions and additional enhancement effects, higher coincidence rates and thinner SPDC sources may be expected. As a prospect, other low-dimensional vdW crystals may also have weak interlayer electronic coupling, resulting in similar and even better NLO effects and SPDC phenomena. Meanwhile, from the perspective view of traditional NLO crystal applications, to realize transparent optical conversion in different spectral regions and avoid heavy laser-induced multi-photon damage, the energy bandgap and single-crystalline quality for 2D materials need to be improved. Anyway, inspired by this research on NbOCl₂, relevant scientists will pay more attention to the NLO-related quantum effects of low-dimensional crystals, which could not only promote the miniaturization and integrability of NLO materials but also facilitate the function expansion of traditional NLO crystals and the further development of optical quantum technology.