Preparation And Properties Of Three Rare Earth Phosphate-based Up-conversion Luminescent Materials

Rare earth up-conversion luminescent materials have attracted more and more attention due to their huge application prospects in the field of luminescence.It is well known that both rare earth doping ions and host materials play a key role in the luminescent properties of luminescent materials.In this paper,three phosphate-based up-conversion luminescent materials such as La₇P₃O₁₈,Y₈P₂O₁₇,and Y₂P₄O₁₃ are used as the research objects.Different rare earth ions are co-doped,and the phosphate-based up-conversion luminescent materials are synthesized by co-precipitation method and high-temperature solid-phase method.By comprehensive thermogravimetric analysis(TG-DSC),X-ray diffraction(XRD),scanning electron microscopy(SEM),ultraviolet-visible diffuse reflectance spectroscopy(UV-Vis),infrared spectroscopy(FT-IR)and up-conversion fluorescence spectroscopy(UPL)to analyze the thermal properties,crystal structure,morphology and optical properties of the as-prepared products.The experimental results are as follows:A series of La₇P₃O₁₈:Ho³⁺,Yb³⁺up-conversion phosphors were successfully prepared by high-temperature solid-phase method.The UV-Vis diffuse reflectance spectra of the samples showed that La₇P₃O₁₈crystal is an indirect semiconductor material with an optical band gap of about 4.10 e V.The effects of different synthesis processes(n(La+Yb+Ho)/n(P)ratio,calcination temperature,rare earth ions doping concentration)on the crystal phase structure and luminescence properties of the samples were investigated.XRD resutls showed that the products prepared in the experiment are mainly a mixture of La₇P₃O₁₈ crystals and a small amount of La PO₄crystals.And the samples obtained under the conditions of n(La+Yb+Ho)/n(P)ratio of 7:3 and calcination temperature of 1500?have good crystallinity and up-conversion luminescence properties.Under the excitation of 980 nm light,the three central wavelengths of blue,green and red light at 486 nm,550 nm and 661 nm can be observed for the Ho³⁺,Yb³⁺co-doped La₇P₃O₁₈phosphors in the range of450-750 nm,respectively,which.corresponding to the ~5F₃?~5I₈,~5S₂/~5F₄?~5I₈,and~5F₅?~5I₈ energy level transitions from Ho³⁺,respectively.Among them,the red emission band at 661 nm dominates the up-conversion luminescence spectra,implying that the samples emit orange-red light.When the doping amount of Ho³⁺and Yb³⁺exceeds 1%and 10%,respectively,the sample will appear concentration quenching phenomenon due to the quadrupole-electric quadrupole interaction.In addition,the up-conversion luminescence pump power dependence of the samples indicates that both the green and red emission bands of the samples originate from the two-photon absorption process.A series of Er³⁺and Yb³⁺co-doped Y₈P₂O₁₇ up-conversion phosphors were successfully prepared by co-precipitation method.The effects of p H,n(Y+Yb+Er)/n(P)ratio,calcination temperature,rare earth ions doping concentration and other experimental conditions on the crystal structure and up-conversion luminescence properties of the samples were investigated.The results show that the obtained product is pure-phase monoclinic Y₈P₂O₁₇ crystal.Under the conditions of the p H of the reaction system is 9.6,the ratio of n(Y+Yb+Er)/n(P)is 5:1,and the calcination temperature is 1500?,the Y₈P₂O₁₇ phosphors with high crystallinity and excellent up-conversion luminescence properties can be obtained.Under the excitation of 980nm light,Er³⁺,Yb³⁺co-doped Y₈P₂O₁₇ luminescent materials.emit three characteristic up-conversion emission bands in the range of 300-800 nm attributed to Er³⁺ions.The blue emission band(~2H_9/2?~4I_15/2)loacted at 410 nm,the green emission band centered at 525/553 nm(~4S_3/2/~2H^11/2?~4I_15/2),and the red emission band observed at662 nm(~4F_9/2?~4I_15/2).Among them,the red emission band at 662 nm of the sample dominates the up-conversion luminescence spectrum,showing an orange-red light,indicating that the Er³⁺,Yb³⁺co-doped Y₈P₂O₁₇ phosphor is a potential orange-red up-conversion luminescent material.In addition,the pump power dependence of the up-conversion luminescence of the samples indicates that the blue,green and red up-conversion emission of Y₈P₂O₁₇ phosphors all follow a two-photon absorption process.A series of Tm³⁺and Yb³⁺co-doped Y₂P₄O₁₃ up-conversion luminescent materials were prepared by co-precipitation method.The crystal structure and luminescence properties of the samples were investigated by XRD,fluorescence spectroscopy and other characterization methods.The results show that the as-synthesized products are mainly a mixture of Y₂P₄O₁₃ crystals and a small amount of YPO₄ crystals.The rare earth ions doped Y₂P₄O₁₃ crystals obtained under p H is 4,n(Y+Yb+Tm)/n(P)is 1:2,and the calcination temperature is 900?,exhibit good phase purity and excellent up-conversion luminescent properties.For Tm³⁺,Yb³⁺co-doped Y₂P₄O₁₃ phosphors,under the excitation of 980 nm near-infrared light,the obtained up-conversion emission spectra are observed with four characteristic emission peaks of Tm³⁺ions in the range of 400-900 nm.The characteristic up-conversion emission bands of Tm³⁺ions are the blue emission band(~1G₄?~3H₆)with the central wavelength of 476 nm,the red emission bands at 652 nm,696 nm,704 nm(~1G₄?~3F₄,~3F₂/~3F₃?~3H₆)and the infrared emission band at 802 nm(~3H₄?~3H~6),respectively,in which the intensity of blue emission band is significantly stronger than that of other emission bands.When the doping amount of Tm³⁺and Yb³⁺above 0.1%and 12%,respectively,the concentration quenching phenomenon will be appears.Meanwhile,the CIE coordinates of Tm³⁺and Yb³⁺co-doped Y₂P₄O₁₃phosphors are located in the blue light region,indicating that Tm³⁺,Yb³⁺co-doped Y₂P₄O₁₃ phosphor is a potential blue up-conversion luminescent material.