A general route to thickness-tunable multilayered sheets of sheelite-type metal molybdate and their self-assembled films

A general chemical approach that allows for the facile synthesis of sheelite-type metal molybdate (XMoO4, X = Ca, Sr, Ba) films composed of interconnected multilayered sheets has been developed. The result derived from the initial growth stage implies that the film formation on an appropriate substrate involves several elaborate assembly processes at different length scales: (i) assembly of numerous tiny flakes into integrated layers via "oriented attachment''; (ii) organizing individual layers into crosslinked multilayered sheets; (iii) self assembly of these sheets to form hierarchical films. The thickness of the sheets can be readily controlled by simple variation of the solution volume. Photoluminescence (PL) studies indicate that the XMoO4 films can emit green luminescence with different intensities and centered at different positions, possibly relating to the bivalent cations X2+. This approach represents a successful example for the construction of inorganic minerals with high hierarchy in the absence of any organic additives and matrices.