| In this paper,the Er3+,Yb3+ doped/co-doped rare earth stannate Ln2Sn2O7(Ln=La,Gd,Y)and rare earth zirconate Ln2Zr2O7(Ln=La,Gd,Y)up-conversion luminescent materials were synthesized by hydrothermal method or polyacrylamide gel technique.The phase structures,sizes,morphologies,optical properties,and up-conversion luminescence efficiency of the as-prepared samples were studied by X-ray diffraction(XRD),scanning electron microscopy(SEM),ultraviolet-visible diffuse emission(UV-vis)and up-conversion luminescence(UPL).The effect of preparation conditions and doping amount of Er3+and Yb3+ions on the phase structures and up-conversion luminescence properties of the as-synthesized stannate Ln2Sn2O7(Ln=La,Gd,Y)and zirconate Ln2Zr2O7(Ln=La,Gd,Y)up-conversion luminescent materials were also investigated.Through experimental research,some innovative results have been achieved.The influence of hydrothermal preparation conditions,such as pH values of reaction system,hydrothermal reaction temperatures,and hydrothermal reaction times,on the the phase structure and up-conversion luminescence properties of the obtianed Er3+ doped La2Sn2O7 samples were studiedup-conversion.XRD results show that the pyrochlore strucutre La2Sn2O7:Er3+ crystals combined with trace impurity phase(or phases)can be obtianed under different pH conditions.The impurity phase composition of the as-prepared samples was SnO2,and gradually changed as the mixed phase with SnO2 and La2O3 with the increase of pH.The samples synthesized at a hydrothermal reaction temperature is 180? and a reaction time is 24 h has a suitable grain size and a perfect crystallinity.The as-synthesized La2Sn2O7:Er3+ samples exhibit several up-conversion emission peaks located at 529 nm,549 nm,and 663 nm when excited by a wavelength of 980 nm light.The up-conversion photoluminescence results of the as-obtained samples indicate that the La2Sn2O7:Er3+ sample synthesized with the doping amount of Er3+ ions is 7 at%,the reaction temperature is 180?,the reaction time is 24 h,and the pH condition is 12,display excellent up-conversion luminescence performance.Up-conversion luminous efficiency analysis results imply that the up-conversion emission peaks located at 549 nm and 663 nm of the La2Sn2O7:7 at%Er3+sample belong to the two-photon absorption emission mechanism,while the intensities of the up-conversion emission peak at 529 nm are inconsistent with the two-photon absorption emission mechanism due to the presence of non-radiative transitions.A hydrothermal route was established to synthesize Yb3+co-doped Ln2Sn2O7:7 at%Er3+,x at%Yb3+(Ln=La,Gd,Y)up-conversion luminescent materials.The effects of different Yb3+ doping amounts on the phase structure and up-conversion luminescence properties of the as-obtianed Ln2Sn2O7:7 at%Er3+,x at%Yb3+(Ln=La,Gd,Y)up-conversion luminescent materials were investigated.XRD results indicate that the as-prepared samples are all the pure pahse of Yb3+ co-doped Ln2Sn2O7:7 at%Er3+,x at%Yb3+(Ln=La,Gd,Y)crystals with pyrochlore structure.The XRD patterns of the samples show a certain offset compared with the standard XRD patterns of Ln2Sn2O7(Ln=La,Gd,Y),implying that the Yb3+and Er3+ ions doped into Ln2Sn2O7(Ln=La,Gd,Y)lattice.Under 980 nm light excitation,the as-prepared Ln2Sn2O7:7 at%Er3+,x at%Yb3+(Ln=La,Gd,Y)samples show three up-conversion emission bands with different intensities located at around 529 nm,540 nm,and 663 nm,which originating from the ZH11/2?4I15/2,4S3/2?4I15/2 and 4F9/2?4I15/2 transitions of Er3+ ions,respectively.The up-conversion emission spectra analysis results show that the quenching concentrations of the as-prepared Ln2Sn2O7:7 at%Er3+,x at%Yb3+(Ln=La,Gd,Y)samples depend on the photoluminescence-based crystals.The quenching concentration of Yb3+ ions for the La2Sn2O7:7 at%Er3+,x at%Yb3+,Gd2Sn2O7:7 at%Er3+,x at%Yb3+,and Y2Sn2O7:7 at%Er3+,x at%Yb3+samples are 14 at%,9 at%,and 6 at%,respectively.Up-conversion luminous efficiency analysis results indicate that the 2H11/2?4I15/2 transition of Er3+ ions(up-conversion emission peak at 529 nm and 525 nm for the La2Sn2O7:7 at%Er3+,x at%Yb3+ and Gd2Sn2O7:7 at%Er3+,x at%Yb3+ samples,respectively)in accordance with the two-photon absorption emission mechanism for the Ln2Sn2O7:7 at%Er3+,x at%Yb3+(Ln=La and Gd)up-conversion luminescence materials.However,the tow up-conversion peaks at 525 nm and 540 nm of the Y2Sn2O7:7 at%Er3+,x at%Yb3+ samples belong to the two-photon absorption emission mechanism.A polyacrylamide gel technique was developed to synthesize the Yb3+ codoped Ln2Zr2O7:7 at%Er3+(Ln=La,Y,Gd)up-conversion luminescent materials.The effects of preparation conditions,such as pH values of the reaction system,calcination temperatures,calcination times,and Yb3+ doping contents,on the phase structure and up-conversion luminescence properties of the as-prepared Yb3+ codoped Ln2Zr2O7:7 at%Er3+(Ln=La,Y,Gd)up-conversion luminescent materials were investigated.XRD results indicate that the synthesis conditions influence the pahse formation of the as-prepared Yb3+ codoped Ln2Zr2O7:7 at%Er3+(Ln=La,Y,Gd)samples.Under the reaction system pH is 10,the reaction calcination temperature is 900?,and the reaction calcination time is 10 h,the as-synthesized samples are pure phase La2Zr2O7:7 at%Er3+,x at%Yb3+crystals with pyrochlore structure,defective fluorite structure of Y2Zr2O7:7 at%Er3+,x at%Yb3+crystals,and Gd2Zr2O7:7 at%Er3+,x at%Yb3+crystals with defect fluorite structure,respectively.Althougth the XRD patterns of the as-obtained Yb3+codoped Ln2Zr2O7:7 at%Er3+(Ln=La,Y,Gd)samples exhibit a slight offset than that of the standard XRD patterns,implying that the Er3+ and Yb3+ ions doped into the sample lattices The unconversion emission spectra of the as-prepared Ln2Zr2O7:7 at%Er3+,x at%Yb3+(Ln=La,Gd,Y)samples were consistent with the 2H11/2?4I15/2,4S3/2?4I15/2 and 4F9/2?4I15/2 transitions(emission bands around at 525 nm,550 nm,and 661 nm,respectively)of Er3+ ions under 980 nm excitation.The up-conversion emission spectra results of the La2Zr2O7:7 at%Er3+,x at%Yb3+ samples indicate that the different emission bands possess different quenching concentrations of dopant Yb3+ ions.When the Yb3+ doping amount was over 8 at%,the concentration quenching were observed for the emission bands in the region between 500 nm and 575 nm.However,for the emission bands loacted in the red edge(625-725 nm),the quenching concentration of Yb3+ ions was up to 10 at%..The concentration quenching phenomena were also observed in the as-prepared Y2Zr2O7:7 at%Er3+,x at%Yb3+ and Gd2Zr2O7:7 at%Er3+,x at%Yb3+ samples when the Yb3+ doping amount were above 16 at%and 8 at%,respectively.The up-conversion emission spectra of the as-synthesized Ln2Zr2O7:7 at%Er3+,x at%Yb3+(Ln=La,Y,Gd)samples show that the emission peaks at around 525 nm,550 nm,and 661 nm exhibit different emission intensities.The results of up-conversion emission efficiency analysis indicate that the emission peak near 525 nm for the La2Zr2O7:7 at%Er3+,8 at%Yb3+and Y2Zr2O7:7 at%Er3+,16 at%Yb3+ samples belong to the two-photon absorption emission mechanism.However,all the three emission bands at 525 nm,550 nm,and 661 nm of the Gd2Zr2O7:7 at%Er3+,8 at%Yb3+sample are not in accordance with the two-photon absorption emission mechanism.The color coordinate results of the as-synthesized Ln2Zr2O7:7 at%Er3+,x at%Yb3+(Ln=La,Y,Gd)samples indicate that the location of the color coordinates of the Ln2Zr2O7:7 at%Er3+,x at%Yb3+(Ln=La,Y,Gd)samples on the CIE chromaticity diagram can be adjusted by the doping content of Yb3+ions.And the color coordinates of the Ln2Zr2O7:7 at%Er3+,x at%Yb3+(Ln=La,Y,Gd)samples show a regularity of moving between green and red regions with the change of Yb3+doping amount. |
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