By　adopting　a　trilacunary　[A-α-GeW9O34]10−　as　a　precursor　under　hydrothermal　conditions,　a　series　of　novel　4s–4f　cluster　substituted　polyoxometalates　(POMs)　containing　two　types　of　in　situ　generated　lacunary　POM　fragments　have　been　made.　These　compounds　were　characterized　by　single-crystal　X-ray　diffractions,　powder　X-ray　diffractions,　infrared　spectroscopy,　thermogravimetric　analyses,　respectively.　Structural　analyses　indicate　that　these　compounds　constructed　from　a　seven-nuclearity　K-O-Ln　(Ln　=　Dy,　Ho,　Er)　heterometallic　cluster　stabilized　by　mixed　dilacunary　Keggin　[α-GeW10O37]10−/multilacunary　open　Wells-Dawson　[Ge2W18O66]16−　fragments.　Furthermore,　the　solid　luminescent　properties　of　the　compounds　at　room　temperature　were　studied.　©　2019　Elsevier　B.V.