The Preparation,Luminescent Properties And Energy Transfer Mechanism Of Eu³⁺,Sm³⁺/Tb³⁺Co-Doped Double-Molybdate And Phosphate Phosphors

W-LEDs are regarded as a new generation of revolutionary lighting sources due to their long life,high luminance,and energy saving and environmental protection.However,they are extremely limited due to the lack of excellent red phosphors.Eu³⁺-activated phosphors,especially phosphate and molybdate-based phosphors,have high color purity and stable luminescence properties.Therefore,Eu³⁺-activated phosphors are the most promising candidates for white-LED red phosphors.but limited to the narrowband absorption of Eu³⁺,Eu³⁺-activated phosphors have problems with low emission intensity and low light energy conversion.Therefore,it’s the main purpose of this study to broaden the absorption band of Eu³⁺and improve the luminous intensity for developing efficient and stable phosphors.The energy transfer effect provides a feasible way to solve the above problems.Based on the literature research and experience accumulated by the research group,this paper synthesized three series of new fluorescent samples by high-temperature solid-state method:NaLa（MoO₄）₂:Eu³⁺/Sm³⁺,LiLa（MoO₄）₂:Eu³⁺/Tb³⁺,Ba3Gd（P04）3:Sm³⁺/Eu³⁺/A+（Li⁺,Na⁺,K⁺）.The samples were characterized by XRD,EDS,SEM,fluorescence spectra and fluorescence lifetime.The main research results and innovations of this paper are as follows:1.Whether in the NaLa（MoO₄）₂:Eu³⁺/Sm³⁺ samples or in the Ba₃Gd（PO₄）₃:Sm³⁺/Eu³⁺ samples,the energy transfer path between Sm³⁺ and Eu³⁺ ions is that the energy is transferred from the ion ⁴G_5/2 state of Sm³⁺ to the ⁵D₀ state of the Eu³⁺,but their mechanism of action are different depending on the crystal field of the host.For the former,energy transfer from Sm³⁺ to Eu³⁺occurs by quadrupole-quadrupole mechanism,however,the latter is dipole-dipole mechanism.2.The NaLa（MoO₄）₂:Eu³⁺,Sm³⁺ fluorescent samples and the LiLa（MoO₄）₂:Eu³⁺,Tb³⁺ fluorescent samples both have the strongest absorption at 465 nm,and their emission spectra at the 615 nm,which is attributed to ⁵D₀→⁷F₂ electric dipole transition of Eu³⁺,are obviously dominated.The results indicate that the matrix environment plays an important role on the luminescence properties of Eu³⁺ in the Eu³⁺ doped molybdate-based phosphors.At the same time,the potential of Eu³⁺-doped double molybdate-based phosphors as red phosphors for white LEDs excited by blue chips is also demonstrated.3.In Eu³⁺/Sm³⁺/Tb³⁺-doped Ba₃Gd（PO₄）₃ phosphors,there is an energy transfer effect from Gd³⁺ to Eu³⁺/Sm³⁺/Tb³⁺ions,which provides the possibility of developing high-energy ultraviolet light exciting red phosphors.4.In Ba₃Gd（PO₄）₃:Sm³⁺,Eu³⁺,A+（Li⁺,Na⁺,K⁺）phosphors,compared with Li⁺ and K⁺,Na⁺ not only produces the strongest fluorescence emission,but also induces electric-dipole dominated transition（⁵D₀→⁷F₂）and results to obtain the most red color.