Gas-phase as well as sol-gel techniques can be used to access to materials which contain two sorts of solid phases, of which one is mostly acting as the matrix. The choice of the molecular precursor in both processing techniques is crucial to obtain the desired composite product. Single source precursors have advantages over multi source precursors, as they allow a simplified technique and often also lead to purer materials. Moreover, the same precursor may behave similarly in the gas phase or wet process or may behave very differently. In this review composite compounds are discussed with Al2O3mostly acting as a matrix and with Ln2O3(Ln = lanthanide element) acting as a second phase. Two processes for Nd:YAG materials are described in more detail as well as some new alcoholates of lanthanides derived from carbinol substituted by thiophenes.