Nanomaterials of NaBi0.9Eu0.1(MoO4)2 were prepared by a simple coprecipitation method in ethylene glycol medium at room temperature. Substitution of bismuth with lanthanum resulted a single-phase solid solution (NaBi0.9−xLaxEu0.1(MoO4)2, 0.0 ≤ x ≤ 0.9) in the complete range of compositions. The linear relationship observed for unit cell parameters, Raman shifts, and FTIR peak positions with lanthanum concentration confirmed the solid solution formation. The band gap of the NaBi0.9−xLaxEu0.1(MoO4)2 nanomaterials widens from 3.36 to 4.4 eV with increasing La3+ concentration in these solid solutions. These nanomaterials show strong red emission upon excitation with UV−visiblelight. The emission properties of Eu3+ are improving with increasing the La3+ content. The band gap of the solid solution plays a crucial role in the improvement of emission properties and is highly dependent on the excitation wavelength. This improvement is marginal while exciting with 464 nm light due to the reduction in the inter Eu 3+ ion energy transfer brought by the lattice expansion, whereas drastic improvement is observed when exciting at 280 and 394 nm light due to the combined effect of band gap and lattice expansion. The quantum efficiency estimated from emission spectra and excited state lifetime values revealed that NaLa0.9Eu0.1(MoO4)2 nanomaterials are best in the series with ∼70% efficiency. These materials can be a suitable red phosphor for white light-emitting diodes (WLEDs).