| One-dimensional nanostructures have attracted considerable attention due totheir interesting geometries, unique physical and chemical properties, and novelpotential applications. It is generally accepted that one-dimensional nanostructuresprovide a good system to investigate the dependence of electrical and thermaltransport or mechanical properties on dimensionality and size reduction. Many effortshave been devoted to the fabrication of one-dimensional nanomaterials and variousmethods, such as template method, sol-gel method, electron-beam orfocused-ion-beam(FIB) writing, chemical vapor deposition(CVD) method andelectrospinning were used to synthesize the materials. Among the methods mentionedabove, electrospinning is a simple and highly versatile method used to preparecontinuous and homogeneous nanofibers. Recently, different kinds of semiconductoroxide nanofibers such as ZnO，TiO2, Mn2O3and so forth have been synthesized byelectrospinning technique.As an importance n-type semiconductor, SnO2is well known for its wide bandgap, low resistivity, high optical transparency and excellent chemical stability haspotential applications in solid-state gas sensors, solar cells, transparent electrodes，andlight emitting diode. Because size, shape and dimensionality are vital parameters todetermine semiconductor properties, a variety of one-dimensional functional SnO2nanostructures, including nanowires, nanobelts, nanotubes and nanorods werefabricated via different methods. One-dimensional SnO2nanofibers were alsoprepared by electrospinning technology and its gas sensing properties were mainlyinvestigated.The doping of rare earth ions in wide band gap semiconductor often causingsignificant changes in its nature, rare earth ions often show different emission characteristics. In this work, Ln3+（Ln=Eu，Sm，Dy，Tb）doped SnO2nanofibers weresynthesized by electrospinning method for the first time and the morphology, size andluminescence property of the nanofibers were further investigated to find the uniqueproperties of Eu doped SnO2nanofibers and the potential application of them. Themain research works are as follows:1. SnO2：Eu3+nanofibersSnO2：Eu3+nanofibers were synthesized by electrospinning for the first time.SEM results indicate the fibers were formed in an unordered arrangement, the size ofthe fibers is relatively uniform, with an average diameter of about200nm, and noadhesion or breaking of fiber happened, the draw ratio of the fibers is large, and thesurface is relatively smooth. XRD results indicate that the peak positions andintensities of SnO2：Eu3+nanofibers are in good agreement with the standard data ofthe rutile SnO2. The average crystallite sizes(calculated by Debye-Scherrer formulaD=0.89λ/βcosθ) are14.56nm for pure SnO2,11.5nm for1%Eu,9.89nm for3%Eu,8.39nm for5%Eu. XPS test results show the content change trend of variouselements in the samples doped with different proportion of Eu, the results areconsistent with the nominal ratio.Raman results indicate that after Eu doping the two strongest vibration modes ofA1gand B2gof SnO2exhibit a slight red shift and is weakened as the Eu contentincreasing. The weak peaks of the first order Raman active modes of B1gand Egof theEu doped SnO2nanofibers do not appear. After Eu doping there is a peak at288cm-1for the SnO2:Eu3+nanofiber which is caused by the disorder of crystal lattice originedfrom doping. UV visible absorption results indicate that the band gap energy is3.62eV for the as-prepared SnO2nanofibers without Eu doping, which is in agreementwith that of the bulk SnO2(3.6eV). the band gap energies of the as-prepared SnO2nanofibers with1%and3%Eu doping are both2.64eV, and that of SnO2nanofiberswith5%Eu doping is2.94eV, which are all less than that of the as-prepared pureSnO2nanofibers. It is probably due to both the impurity energy level generated in theband gap origined from doping, which is connected with the conduction band and cause band gap decreasing.Fluorescence test results indicate that there is only the orange emission peakwithout red emission peak of Eu3+ions for the as-prepared SnO2nanofibers withdifferent doping contents of Eu3+. Under the excitation of275nm, the orange emissionpeak split into three peaks which located at591,595and600nm respectively, underthe excitation of488nm, the orange emission peak is a broad emission peak in thewavelength range of575—615nm, centering at595nm. There is no red emissionpeak is due to Eu3+ions is dominant at the symmetric lattice point. The intensity oforange emission at the excitation wavelength of275nm is higher than that at theexcitation wavelength of488nm. Moreover, the intensity of orange emission uponindirect excitation increases with the increase of the Eu doping content, indicating thatfor the Eu doped SnO2nanofibers, the energy transfer between the SnO2crystal latticeand the Eu3+ions promotes the luminescence efficiency.In addition, under the excitation of275nm and368nm, the undoped and dopedwith different proportion of samples generated a broad emission band which isbetween350nm and500nm with a series of discrete emission peaks at it, the intensityof these emission peaks is significantly higher than that of Eu3+ions characteristicemission band (575nm to600nm emission). After Eu doping the relative intensity ofthese peaks change, the peak position exhibit a blue shift and there are new peaksappear. These emission peaks originate from the luminescence centers formed by suchoxygen vacancies, tin interstitials or dangling in the present of SnO2, after Eu dopingthese defect levels increase, exhibit a blue shift, and new defect energy levels areintroduced, thus causing significant effects to the intensity the position of theseemission peaks.2. SnO2：Sm3+nanofibersSnO2：Sm3+nanofibers were synthesized by electrospinning for the first time.SEM results indicate the fibers were formed in an unordered arrangement, the size ofthe fibers is relatively uniform, with an average diameter of about100nm, and noadhesion or breaking of fiber happened, the draw ratio of the fibers is large, and the surface is relatively smooth. XRD results indicate that the peak positions andintensities of SnO2：Sm3+nanofibers are in good agreement with the standard data ofthe rutile SnO2. The average crystallite sizes(calculated by Debye-Scherrer formulaD=0.89λ/βcosθ) are24.94nm for1%Sm,24.94nm for3%Sm,11.66nm for5%Sm.Raman results indicate that after Sm doping the two strongest vibration modes of A1gand B2gof SnO2exhibit a slight red shift which is more obvious than that of SnO2：Eu3+nanofibers. The weak peaks of the first order Raman active modes of B1gand Egof the SnO2nanofibers do not appear, but the second order Raman active modes ofA2uappear. After Sm doping there is a peak at301cm-1for the SnO2:Sm3+nanofiberwhich is also caused by the disorder of crystal lattice origined from doping.XPS test results show the content change trend of various elements in thesamples doped with different proportion of Sm, the results are consistent with thenominal ratio. The ratio of lattice oxygen and surface oxygen and the ratio of latticeoxygen and tin ions all decrease with the increase of the content of Sm, this indicatethat the oxygen vacancy increase with the increase of the content of Sm in the latticeof SnO2:Sm3+nanofiber. UV visible absorption results indicate that the band gapenergies of the as-prepared SnO2nanofibers with1%Sm doping is3.61eV, and thatof SnO2nanofibers with3%and5%Sm doping are both3.56eV, which are allslightly less than that of the as-prepared pure SnO2nanofibers(3.62eV).Fluorescence test results indicate that there is no Sm3+ions characteristicemission in the wavelength range of550-660nm, this indicate that Sm3+ion is not avalid excited ion at SnO2:Sm3+electrospinning nanofiber. After Sm doping, a newemisson peak located at375nm appear;there is only changing in the intensity of thesix emission peak of undoped SnO2nanofiber without peak position changing andpeak disappearing after Sm doping. The relative intensity of the new emisson peaklocated at375nm increases with the increase of the Sm doping content and becomethe main peak, this can be attributed to the substitution of Sm3+for Sn4+ions cause theformation of a new oxygen vacancies in the crystal lattice, which introduce donorlevel closer to the conduction band in the band gap. 3. SnO2：Tb3+nanofibersSnO2：Tb3+nanofibers were synthesized by electrospinning for the first time.SEM results indicate the fibers were formed in an unordered arrangement, the size ofthe fibers is relatively uniform, with diameter in the range of100nm to200nm, andno adhesion or breaking of fiber happened, the draw ratio of the fibers is large, andthe surface is relatively smooth. XRD results indicate that the peak positions andintensities of SnO2：Tb3+nanofibers are in good agreement with the standard data ofthe rutile SnO2. The average crystallite sizes(calculated by Debye-Scherrer formulaD=0.89λ/βcosθ) are20.73nm for1%Tb,20.38nm for3%Tb,17.42nm for5%Tb.Raman results indicate that the raman peak of Tb dpoed samples is similar to thatof Sm dpoed samples, after Tb doping the two strongest vibration modes of A1gandB2gof SnO2exhibit a same red shift, the second order Raman active modes of A2ualsoappear, the weak peaks of the first order Raman active modes of B1gand Egof theSnO2nanofibers do not appear yet, the difference is that with the increase of the Tbdoping content, the relative intensity of the Raman peaks decrease and the width ofthe Raman peaks increase, this shows that the crystallinity of fibers decreases with theincrease of Tb content, Raman spectra of Eu and Sm doped samples were free of thislaw.XPS test results show the content change trend of various elements in thesamples doped with different proportion of Tb, the results are consistent with thenominal ratio. The ratio of lattice oxygen and surface oxygen and the ratio of latticeoxygen and tin ions all decrease with the increase of the content of Tb, this indicatethat the oxygen vacancy increase with the increase of the content of Tb in the latticeof SnO2:Tb3+nanofiber. UV visible absorption results indicate that the band gapenergies of the as-prepared SnO2nanofibers with1%and3%Tb doping is3.60eV,and that of SnO2nanofibers with5%Tb doping are both3.50eV, which are allslightly less than that of the as-prepared pure SnO2nanofibers(3.62eV).Fluorescence test results indicate that there is no Tb3+ions characteristicemission for Tb doped samples, this indicate that Tb3+ion is not a valid excited ion at SnO2:Tb3+electrospinning nanofiber. After Tb doping, new emisson peaks located at375nm,453nm,496nm appear respectively; there is only changing in the intensity ofthe six emission peak of undoped SnO2nanofiber without peak position changing andpeak disappearing after Tb doping. The above characteristics are part similar to Euand Sm doped samples. What is different from Sm doped samples is that after Tbdoping the relative intensity of375nm peak is higher than471nm peak for1%Tbdoping and then increases continuely with the increase of the Tb doping content andbecome the main peak, and the relative intensity of471nm peak has no change.4. SnO2：Dy3+nanofibersSnO2：Dy3+nanofibers were synthesized by electrospinning for the first time.SEM results indicate the fibers were formed in an unordered arrangement, the size ofthe fibers is relatively uniform, with an average diameter of about100nm, and noadhesion or breaking of fiber happened, the draw ratio of the fibers is large, and thesurface is relatively smooth. XRD results indicate that the peak positions andintensities of SnO2：Dy3+nanofibers are in good agreement with the standard data ofthe rutile SnO2. The average crystallite sizes(calculated by Debye-Scherrer formulaD=0.89λ/βcosθ) are15.59nm for1%Dy,10.60nm for3%Dy,10.29nm for5%Dy.The characteristic of Raman spectrumof Dy doped samples is simlar to that of Sm andTb doped samples.XPS test results show the content change trend of various elements in thesamples doped with different proportion of Dy, the results are consistent with thenominal ratio. The ratio of lattice oxygen and surface oxygen and the ratio of latticeoxygen and tin ions all decrease with the increase of the content of Dy, this indicatethat the oxygen vacancy increase with the increase of the content of Dy in the latticeof SnO2:Dy3+nanofiber. UV visible absorption results indicate that the band gapenergies of the as-prepared SnO2nanofibers with1%,3%,5%Dy doping is3.38eV,3.49eV,3.51eV respectively, which are all slightly less than that of the as-preparedpure SnO2nanofibers. Compared with the Sm and Tb doped samples, there is moreobvious reduction of the band gap energies for Dy doped samples. Fluorescence test results indicate that there is no Dy3+ions characteristicemission for Dy doped samples, this indicate that Dy3+ion is not a valid excited ion atSnO2:Dy3+electrospinning nanofiber. The effect of Dy doping on photoluminescenceof SnO2nanofibers is part same with Tb, Sm and Eu doping, but there has thecertain difference, the left part of the energy level transition luminescence schematicdiagram of Dy doped samples is same with that of Tb doped samples, and the rightpart is same with that of Eu doped samples. Compared with the Sm and Tb dopedsamples, The intensity of375nm peak is strongest for5%Dy doped samples.Through the research, we have knew the unique photoluminescence properties ofSnO2:xLn3+(Ln=Eu，Sm，Tb，Dy) system with morphology of nanofibers, and haveexplored the intrinsic physical mechanism, laid a solid foundation for the preparationof novel luminescent materials based on one-dimensional structure by electrospinningtechnique in the future. |
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