Here, we report a series of two-dimensional lanthanide metal-organic frameworks Ln-DBTPA (where DBTPA = 2,5-dibromoterephthalic acid and Ln = Tb (1), Eu (2), or Gd (3)) showing a unique turn-up responsiveness toward ultraviolet (UV) radiation. The luminescence enhancement was derived from the accumulated radicals that can promote the intersystem crossing process. The compound 1 shows an ultralow detection limit of 9.1 × 10-9 J toward UV radiation, representing a new type of luminescent UV detectors.