Luminescence Of Yb³⁺/Nd³⁺ Ions In Different Substrates And Study Of Sensitization

Recently, earth Yb³⁺/Nd³⁺doped inorganic materials of near-infrared （NIR） luminescencehave attracted significant attention due to their many advantages such as strong penetrability,narrow emission spectra, large stokes shift, long-live and free of background for biologicalanalysis. However, the NIR luminescence of Yb³⁺/Nd³⁺doped inorganic materials is still weak,which is the difficulty for their application. There are two important ways to enhance theluminescence intensity: one way is through the energy transfer between sensitizer andYb³⁺/Nd³⁺, another way is through the energy transfer between substrate and Yb³⁺/Nd³⁺. Bi³⁺isan important sensitizer and activator with allowed [Xe]6s²electronic configuration, containingthe6s²ground state and6s6p first excited state, which prone to deformation. Moreover,fluorescence emission peak of Bi³⁺dependents on substrate lattice with a significant changefrom the ultraviolet to infrared, the transition to a highly efficient absorption and emission. Inthis paper, we dedicate to improve the NIR luminescence by using proper hosts and sensitizedion Bi³⁺. The hosts and Bi³⁺can improve the NIR luminescence intensity by transferring energyto Yb³⁺/Nd³⁺. The conclusions and results were summarized as follows:Novel red-emit phosphor for W-LED, Na₂Ca₄（1-x-y）（PO₄）2SiO₄:Eu³⁺,Bi³⁺was synthesizedby conventional solid-state reaction. Effects of the H₃BO₃flux, the re-calcination time anddoping concentrations of Eu³⁺/Bi³⁺on the luminescence properties were investigated. It wasfound that α-Na₂Ca₄（PO₄）2SiO₄, which is favorable to get a higher Eu³⁺emission intensity, canbe obtained if H₃BO₃was added as flux. Samples re-calcined at1200°C for1.5h and dopedwith4%Eu³⁺,1%Bi³⁺give the strongest red emission.NIR luminescence material Na₂Ca₄（PO₄）2SiO₄:Eu³⁺,Yb³⁺and Na₂Ca₄（PO₄）2SiO₄:Nd³⁺were synthesized by high temperature solid state method. The effect of Eu³⁺/Yb³⁺/Nd³⁺concentration on luminescence properties was investigated. The result showed that the dopingof Eu³⁺can improve the NIR luminescence through enhancing the intensity of Yb³⁺luminescence in Na₂Ca₄（PO₄）2SiO₄, the optimum doping contents of Eu³⁺and Yb³⁺are4%and1%, respectively. We have analyzed the energy transfer mechanism between Eu³⁺and Yb³⁺:quantum cutting from Eu³⁺to Yb³⁺, Eu³⁺can sensitize near-infrared luminescence of Yb³⁺. The intensity of the NIR luminescence reached maximum when the concentration of Nd³⁺is2%inNa₂Ca₄（PO₄）2SiO₄.NIR luminescence materials MMoO4:Yb³⁺,Bi³⁺（M=Ca, Sr, Ba） were prepared by hightemperature solid state method. It was found that Bi³⁺can effectively transfer energy to Yb³⁺and Bi³⁺can sensitize the NIR luminescence of Yb³⁺. Effects of the calcination temperature, there-calcination time and doping concentrations of Yb³⁺/Bi³⁺on the luminescence properties wereinvestigated. The intensity of the NIR luminescence reached maximum whenCaMoO₄:Yb³⁺,Bi³⁺samples re-calcined at700°C for1h and doped with4%Yb³⁺,4%Bi³⁺;SrMoO₄:Yb³⁺,Bi³⁺samples re-calcined at1200°C for1h and doped with3%Yb³⁺,2%Bi³⁺andBaMoO4:Yb³⁺,Bi³⁺samples re-calcined at700°C for1h and doped with3%Yb³⁺,3%Bi³⁺. Theenergy transfer efficiency between Bi³⁺and Yb³⁺in CaMoO₄is much higher than other twokinds of hosts.Near-infrared （NIR） luminescence phosphors Yb³⁺/Nd³⁺, Bi³⁺co-doped YVO₄have beenprepared by conventional solid state method and the sensitization of Yb³⁺/Nd³⁺near-infraredluminescence by Bi³⁺is investigated. It was found that when co-doping Bi³⁺, the characteristicNIR luminescence of Yb³⁺/Nd³⁺in YVO₄matrix was greatly enhanced, the strongest site of theexcitation wavelength red-shifted and the wavelength range of the excitation spectrumbroadened. The possible energy transfer mechanism among VO43-, Bi³⁺and Yb³⁺/Nd³⁺was alsodiscussed. The possible energy transfer processes are VO43-â†'Bi-O, V-Oâ†'Yb³⁺QC inYVO₄:Yb³⁺,Bi³⁺and VO₄^3-â†'V⁵⁺-Bi³⁺â†'Nd³⁺in YVO₄:Nd³⁺,Bi³⁺, the efficiency of energytransfer respectively up to171%and88%.NIR luminescence materials Sr2CeO4:Yb³⁺/Nd³⁺were prepared by high temperature solidstate method. The effect of preparation conditions on luminescence properties was investigated.And the energy transfer mechanism between Sr2CeO4host and Yb³⁺/Nd³⁺was also discussed,there may be two ways:â‘ CeO₄^4-（LS）â†'Yb³⁺-O^2-/Nd³⁺-O^2-â†'Yb³⁺/Nd³⁺,â‘¡CeO₄^4-（MLCT）â†'Yb³⁺/Nd³⁺.