A wide range of optical bandgap modulation up to 5.1 eV was achieved for quaternary BeMgZnO thin films prepared using plasma assisted molecular beam epitaxy, enabling development of UV emitters and solar-blind photodetectors. The significantly improved structural quality and bandgap widening in BeMgZnO layers as compared to those of BeZnO and MgZnO ternaries indicate enhanced incorporation of both Be and Mg on Zn sites in the wurtzite lattice. Correlation of lattice parameters with optical bandgaps reveals that co-alloying MgO and BeO with ZnO helps overcome the impediment of limited bandgap extension offered by the corresponding ternary compounds due to phase separation and allows lattice-matched or nearly lattice-matched BeMgZnO/ZnO heterostructures. Optimization of growth conditions at higher Mg and/or Be fluxes is expected to provide bandgaps beyond 5.1 eV. Published by Elsevier B.V.