•The mono-SmIII substituted phosphotungstate.•Organic–inorganic hybrid mono-lanthanide substituted polyoxometalates with amino acids.•IR spectra and UV spectra of 1:2-type [Sm(α-PW11O39)2]11− containing polyoxotungstates.•Solid-state photoluminescence of mono-SmIII substituted phosphotungstate.•Polyoxometalate-based ferroelectric material.An organic–inorganic hybrid mono-SmIII substituted phosphotungstate KNa3[HPro]7[Sm(α-PW11O39)2]·Pro·18H2O (1) (Pro = d-proline) has been synthesized in the conventional aqueous solution and structurally characterized by elemental analyses, inductively coupled plasma atomic emission spectrometry (ICP-AES) analyses, IR spectra, UV spectra, powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA) and single-crystal X-ray diffraction. The molecule of 1 consists of a classical 1:2-type [Sm(α-PW11O39)2]11− fragment and free d-proline components. It should be pointed out that the synergistic action between the in-situ formed chiral [Sm(α-PW11O39)2]11− fragment and chiral d-proline components results in the formation of the chiral 1. The luminescence emission of 1 reveals three characteristic bands that derive from the 4G5/2 → 6H5/2, 4G5/2 → 6H7/2 and 4G5/2 → 6H9/2 transitions of the SmIII cation as well as the synergistic contribution of the O → W transitions of [α-PW11O39]7− moieties and a π*–n or π*–π transitions of Pro. Its ferroelectric behavior has been measured.Graphical abstractAn organic–inorganic hybrid mono-SmIII substituted phosphotungstate with amino acids has been synthesized and IR, UV spectra, the photoluminescence spectra and ferroelectric behavior have been studied.