Molten Salt Synthesis And Luminescent Properties Of Rare-Earth Ions-Doped Nanophosphors

Rare-earth doped nanophosphors, including LnV04(Ln=Y, Gd), LnP04(Ln=Y, Gd) and YNbO4 were synthesized by molten salt method. The luminescence and luminescent kinetic properties of rare earth ions such as Eu3+, Dy3+ and Sm3+ were studied in these nanophosphors.SEM and TEM results indicated that as prepared nanophosphors show regular morphology, uniform particle size and excellent dispersity, among which, LnV04(Ln=Y, Gd) exhibits cubic morphology, LnPO4(Ln=Y, Gd) exbits nano-band clusters. Due to the low reaction temperature and reutilization of molten salt, molten salt synthesis is an ideal, environmentally friendly method to synthesis of nanophosphors.YVO4:Re(Re=Eu3+, Dy3+), GdVO4:Eu3+, YPO4:Re(Re=Eu3+, Sm3+) and GdPO4:Eu3+ was synthesized in equal moles of NaN03 and KNO3 molten salt medium. The results show that in YVO4:Eu3+ nanophosphors, the emission excited by ultraviolet is dominated by the 621 nm red emission ascribed to 5D0-7F2 transition and the optimized doping concentration of Eu3+ is 5.0 mol%. The emission of YVO4:Dy3+ is dominated by the 575 nm yellow light ascribed to4F9/2-6H13/2, the optimized concentration is 2.0 mol%. There exists an efficient energy transfer from VO43- to Eu3+ and Dy3+. The decay curves of Eu3+ and Dy3+ emission can be well fitted into a double exponential decay. In GdVO4:Eu3+ nanophosphors, the emission of Eu3+ is also dominated by the red emission originated from 5D0-7F2, the decay curves of Eu3+ can be fitted into a single exponential decay, the optimized concentration is 5.0 mol%.In YPO4:Re (Re=Eu3+, Sm3+) nanophosphors, the emission of Eu3+ is dominated by the 595 nm orange-red light ascribed to 5D0-7F1 transition. The optimized concentration of Eu3+ is 5.0 mol%. The emission of Sm3+ is dominated by the 603 nm red light ascribed to4G9/2-6H7/2 and the optimized concentration of Sm3+ is 1.0 mol%. The decay curves of Eu3+ and Sm3+ can be fitted into a single exponential decay. In GdPO4:Eu3+ nanophosphors, the emission of Eu3+ is dominated by the orange-red light due to 5D0-7F1.This results indicated that though Eu3+ occupied the C1 site, as a result of the influence of PO43-, its central symmertry is not high. The decay curves of Eu3+ can be well fitted into a single exponential decay, the optimized concentration is 7.0 mol%.YNbO4:Eu3+ nanophophors were successfully prepared by molten salt synthesis where was used as reaction medium. The crystallite phase of YNbO4:Eu3+ nanocrystallines transformed from tetragonal phase to monoclinic phase with the increase of annealing temperature, and the grain size of YNbO4:Eu3+ nanocrystallines increase with annealing temperature, too. YNbO4:Eu3+ nanophophors show red emission due to the 5D0-7F2 of Eu3+, which indicates that Eu3+ occupied a site without inversion center. The emission intensity of YNbO4:Eu3+ in nanocrystallines increase with the increase annealing temperature.