Nonlinear metal-organic framework crystals: from bulk to nanometer scales

Metal–organic frameworks (MOFs) have emerged as a new family of nonlinear optical (NLO) crystals. Here, we explore MOFs as ultrathin NLO crystals for light generation and nonlinear frequency conversion. At the nanoscale, lanthanide-based MOF (Ln-MOF) nanosheets exhibit nonlinear enhancement of photoluminescence (PL) upon thickness reduction and temperature variation. At the microscale, a non-centrosymmetric MOF microcrystal enables broadband, multiwavelength coherent light generation through second- and third-order nonlinear processes at a fixed crystal orientation. These findings demonstrate that rationally engineered MOFs can bridge nanoscale light emission and microscale nonlinear optics, offering scalable and efficient solutions for next-generation nonlinear photonics.