Enhanced emission intensity in (Li+/Ca2+/Bi3+) ions co-doped NaLa(MoO4)2: Dy3+phosphors and their Judd-Ofelt analysis for WLEDs applications

In the present study, we have synthesized a series of Dy3+ ion doped NaLa(MoO4)(2)phosphors by the conventional solid-state method at 750 degrees C for 4h. All the compounds were crystallized in the tetragonal scheelite type structure with space group (I41/a, No.88). The morphology and functional group were confirmed by the field emission scanning electron microscopy (FE-SEM) and Fourier transform infrared(FTIR)spectroscopy. Upon near-Ultraviolet (n-UV) excitation, the PL spectra exhibit the two characteristic emissions of Dy3+ ions, blue (F-4(9/2) -> H-6(15/2)) at 487 nm and yellow (F-4(9/2) -> H-6(13/2)) at 574nm respectively. The optimum concentration of Dy(3+)ionis 3 mol% and then quenching occurred due to multipolar interaction. Further, enhanced the emission intensity by co-doping with monovalent (Li+), divalent (Ca2+) and trivalent (Bi3+) ions. Among them, Li+ ion co-doped samples are shown maximum intensity (50 times) more than Dy3+ doped phosphors as relaxation of parity restriction of electric dipole transition because of local distortion of crystal field around the Dy3+ ions. In addition, by incorporation of Eu3+ ions into NaLa(MoO4)(2):Dy(3+)system, tuned the emission color from white to red, owing to energy transfer from Dy3+ to Eu3+ ions. The intensity parameters (omega(2), omega(4)) and radiative properties such as transition probabilities (A (T)), radiative lifetime (tau (rad)), and branching ratio were calculated using the Judd-Ofelt theory. CIE color coordinates, CCT values indicates that these phosphors exhibit an excellent white emission. The determined radiative properties, CIE and CCT results revealed that the Dy3+-activated NaLa(MoO4)(2)phosphors are potential materials for developing white LEDs, and optoelectronic device fabrications.