A luminescence quantum yield of 7.8% was obtained for a quaternary mixed-ligand samarium complex; this value is higher than those previously reported in the literature for such complexes in solution. The complex was prepared by microwave-assisted synthesis in 15 min with a yield of 69%; that is similar to 400 times faster than the usual synthesis that required 4 days and led to a yield of only 30%. Therefore, we propose microwave-assisted synthesis as the method of choice for preparing mixed-ligand lanthanoid complexes.