Probing the Structure of NaYF4 Nanocrystals using Synchrotron-Based Energy-Dependent X-ray Photoelectron Spectroscopy

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dc.contributor.authorPichaandi, Jothirmayanantham
dc.contributor.authorDas, Gautom Kumar
dc.contributor.authorJohnson, Noah J. J.
dc.contributor.authorRegier, Tom
dc.contributor.authorvan Veggel, Frank C.J.M.
dc.date.accessioned2016-08-26T12:50:12Z
dc.date.available2016-08-26T12:50:12Z
dc.date.copyright2014en_US
dc.date.issued2014-09
dc.description.abstractUnderstanding the structure and chemical speciation of the synthesized lanthanide-doped NaYF4 nanocrystals is of paramount importance to improve and optimize their physical and chemical properties. Hence in this work we employ synchrotron-based high-resolution X-ray photoelectron spectroscopy (XPS) measurements to analyze lanthanide-doped and undoped NaYF4 nanocrystals. These measurements revealed that there are two doublets for the yttrium ions in the nanocrystal instead of the single doublet in case all Y3+ ions have the same chemical environment, generally observed around a binding energy of 160 eV (3d photoelectrons of Y3+). This second doublet (binding energy ∼ 157.5 eV) was convoluted with the first doublet (binding energy ∼ 160 eV), and the intensity of this doublet increased with a decrease in excitation X-ray energy. The second doublet was confirmed to belong to the yttrium ions as doped and undoped NaYF4 nanocrystals exhibit this second peak. The peaks were deconvoluted showing that the second peak is also a doublet with the ratio of the peaks being 2:3. This is exactly the same as what we have observed for the first doublet of the 3d photoelectrons of yttrium ions. In addition, we observe an increase in intensity of the second doublet in comparison to the original 3d doublet of the yttrium ions as the excitation energy is decreased. This suggests that the second doublet is from surface yttrium ions in the NaYF4 nanocrystal. To confirm our hypothesis, a shell of NaYbF4 or NaTmF4 was grown over the NaYF4 nanocrystal and the second doublet for the yttrium ions was not observed. This is an additional confirmation that the second doublet is indeed from the surface yttrium ions. This implies that the yttriums on the surface of the nanocrystals have a (slightly) different chemical speciation than their counterparts inside the nanocrystals. We attribute the new chemical speciation of surface yttrium ions to the different chemical environment they encounter than their counterparts inside the nanocrystal.en_US
dc.description.reviewstatusRevieweden_US
dc.description.scholarlevelFacultyen_US
dc.description.sponsorshipThis work was supported by National Science and Engineering Research Council (NSERC) and Canadian Light Source (CLS), Saskatoon.en_US
dc.identifier.citationPichaandi, J., Das, G.K., Johnson, N.J.J., Regier, T., & van Veggel, F.C.J.M. (2014). Probing the Structure of NaYF4 Nanocrystals using Synchrotron-Based Energy- Dependent X-ray Photoelectron Spectroscopy. Journal of Physical Chemistry C, 118(37), 21639-21646.en_US
dc.identifier.urihttp://dx.doi.org/10.1021/jp505646j
dc.identifier.urihttp://hdl.handle.net/1828/7485
dc.language.isoenen_US
dc.publisherJournal of Physical Chemistry Cen_US
dc.subjectNanocrystals
dc.subjectLanthanides
dc.subjectChemical speciation
dc.subjectUpconversion
dc.subjectSurface ions
dc.subjectX-ray Photo-electron Spectroscopy (XPS)
dc.subject.departmentDepartment of Chemistry
dc.titleProbing the Structure of NaYF4 Nanocrystals using Synchrotron-Based Energy-Dependent X-ray Photoelectron Spectroscopyen_US
dc.typePostprinten_US

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