For the first time, an unprecedented 3D framework based on lanthanide-containing Nb/W mixed-addendum polyoxometalate [H₃La₈(H₂O)₃₂(C₆H₅NO₂)₆][SiW₉Nb₃O₄₀]₃·8H₂O (1) has been obtained by utilizing the steam-assisted conversion method. Meanwhile, the stability, electrochemical behavior, and photoluminescence properties of 1 have also been discussed.