A new strategy has been developed to enhance the optical bandwidths of rare earth dopants by partial substitution of the divalent cation (D) in the original DWO(4) or DMoO(4) crystal structures. For demonstration, the monoclinic (space group C2/c) Yb-doped Li(0.75)Gd(0.75)Ba(0.5)(MoO(4))(2) crystal was grown in a Li(2)Mo(2)O(7) flux, and 300 K Yb(3+) laser operation is reported. The laser emission is characterized by rather short wavelengths related to the specific features of the absorption and emission spectra, which leads to very small quantum defect, i.e., as low as 0.7% for E//b-axis. Using a Ti:sapphire laser at 976.6 nm, up to 295 mW of cw power are obtained without special cooling while the tunability range extends over 33 nm around 1020 nm.