Blue-Light-Excited Eu3+/Sm3+ Co-Doped NaLa(MoO4)2 Phosphors: Synthesis, Characterizations and Red Emission Enhancement for WLEDs
The system NaLa(MoO4)2:Eu3+/Sm3+ phosphors were prepared by solid-state reaction followed by heat treatment at 450–600 °C. As shown by X-ray powder diffraction, the phosphors had a body-centered tetragonal structure, high phase purity and high crystallinity. The photoluminescence measurements carried out under excitation at 464 nm indicated the main emission at about 615 nm corresponding to the electric dipole transition 5D0→7F2 of Eu3+, which agreed well with the emission wavelengths of the GaN-based blue LED chips. In NaLa(MoO4)2:Eu3+/Sm3+ phosphors, Sm3+ can efficiently transfer excitation energy to Eu3+, which resulted in a significant improvement of the fluorescence intensity, and the fluorescence intensity of the phosphors calcined at 550 °C maximized at the doping concentrations of Eu3+ and Sm3+ of 15.0 and 2.0 mol %, respectively. The decay curves and CIE (Commission Internationale de L’ Eclairage) coordinates of Sm3+ or/and Eu3+ doped phosphors were analyzed for the investigation of the energy transfer mechanism and color variation trend. Thus, NaLa(MoO4)2:Eu3+,Sm3+ can be classified as a potential red-emitting phosphor for white light-emitting diodes (WLEDs).