Synthesis And Luminescence Properties Of Rare-earth Ions Doped Molybdate Multicolor Fluorescent Materials

The rare earth molybdate can be used as a good luminescent matrix material owning to its great chemical stability as well as the strong and wide charge transfer absorption band in the near ultraviolet region.Under the excitation of ultraviolet light,the molybdate matrix can not only produce high efficiency fluorescence,but also transfer energy to the doped rare earth ions in the form of non-radiation for the sake of enhancing rare earth ions'luminescence.Furthermore,by adjusting the species and amount of the doped rare earth ions,the multicolor fluorescent materials can be obtained.In this dissertation,based on the LiGd?MoO₄?₂ matrix material,multicolor luminescence was achieved by doping different rare earth ions(Dy³⁺,Eu³⁺,Tb³⁺,Sm³⁺,Er³⁺),the energy transfer mechanism and luminescent properties were studied in detail.The main contents are as follows:Series of Dy³⁺and Eu³⁺co-doped LiGd?MoO₄?₂ phosphors were prepared via sol-gel method.The phosphors exhibit yellow emission of Dy³⁺and red emission of Eu³⁺upon 354nm ultraviolet light excitation.The critical distance of Dy³⁺and Eu³⁺is calculated to be13.83?.The energy transfer from Dy³⁺to Eu³⁺is occurred.The mechanism of energy transfer is dipole-quadrupole interaction.By adjusting the concentration of Dy³⁺and Eu³⁺,the phosphor can be observed the warm-white-light emitting.Moreover,the relationship between the value of correlated color temperature for warm-white-light and the doped rare earth ions(Dy³⁺,Eu³⁺)concentration was studied in detail.According to these above results,one can see that the synthesized phosphors have potential applications in the field of white LED.Series of Tb³⁺and Sm³⁺co-doped LiGd?MoO₄?₂ phosphors were prepared via sol-gel method.In LiGd?MoO₄?₂:Tb³⁺and LiGd?MoO₄?₂:Sm³⁺phosphors,MoO₄^2-group can absorb near ultraviolet light and transfer energy to Tb³⁺and Sm³⁺.The green emission of Tb³⁺and the orange-red emission of Sm³⁺could be observed in the emission spectra of LiGd?MoO₄?₂:0.01Tb³⁺,xSm³⁺phosphors under the excitation of 287 nm ultraviolet light.The tunable color of the phosphors can be realized by changing the doping concentration of Sm³⁺and the excitation wavelength.Series of LiGd?MoO₄?₂:Er³⁺,Eu³⁺phosphors were prepared via sol-gel method.In the phosphors of LiGd?MoO₄?₂:Er³⁺and LiGd?MoO₄?₂:Eu³⁺,the host will transfer the absorbed energy to Er³⁺and Eu³⁺,respectively.Under 379 nm near ultraviolet light excitation,the characteristic green emission of Er³⁺and the red emission of Eu³⁺could be observed in the emission spectra of LiGd?MoO₄?₂:Er³⁺,xEu³⁺phosphor.The tunable luminescence color of LiGd?MoO₄?₂:0.04Er³⁺,0.22Eu³⁺phosphor at different excitation wavelengths was realized.