Mechanism of morphology formation and energy transfer of NaLa(WO4)2:Sm3+:Eu3+ phosphors

A series of phosphors of Sm3+ and Eu3+ single-doped or co-doped NaLa(WO4)(2) matrix are synthesized with the hydrothermal method. The structure, morphology, luminescent properties, quantum efficiency and CIE coordinates of sample are characterized and analyzed with X-ray diffraction (XRD), scanning electron microscopy (SEM and EDS), transmission electron microscope (TEM), fluorescence spectrophotometer (FL) and UV-Vis (UV) absorption spectra. The results show that all the obtained products have the scheelite structure with spherical or ellipsoidal shapes. The morphology formation mechanism is proposed as follows: nucleationdissolutionrecrystallizationcrystal growth (self-assembly process). Under 393- and 403-nm photoexcitation, NaLa (WO4)(2):Sm3+:Eu3+ emits intense red and orange red light. In NaLa (WO4)(2): Sm3+:Eu3+ sample, the energy transfer can occur from Sm3+ to Eu3+, and the critical distance of energy transfer is between 1.655 and 2.362nm. The energy transfer mechanism is electric dipole-electric dipole interaction. The energy transfer efficiency can be over 70%. The best product NaLa(WO4)(2):2%Sm3+:4%Eu3+ has a luminous efficiency of 54.70%. The CIE coordinates are X=0.6585, Y=0.3404.