Spectroscopic determination of site symmetry and space group in lanthanide-doped crystals: Resolving intricate symmetry aspects for β-NaLnF₄

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• 作者：Mirosław Karbowiak^a ; ^{miroslaw.karbowiak@chem.uni.wroc.pl" class="auth_mail" title="E-mail the corresponding author} ; Jakub Cichos^a ; Czesław Rudowicz^b ; ¹ ; ^{czerud@amu.edu.pl" class="auth_mail" title="E-mail the corresponding author}
• 关键词：Lanthanides ; NaYF4 ; Photoluminescence ; Structure elucidation ; Symmetry
• 刊名：Polyhedron
• 出版年：2016
• 出版时间：17 February 2016
• 年：2016
• 卷：105
• 期：Complete
• 页码：42-48
• 全文大小：837 K

文摘

There exists a controversy in the hitherto reported studies concerning the actual space group that accounts for spectroscopic results observed for the trivalent lanthanide (Ln³⁺) ions doped into β-NaLnF₄ hosts. The two competing assignments of the space group: P  class="mathmlsrc">title="View the MathML source" class="mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0277538715007391&_mathId=si1.gif&_user=111111111&_pii=S0277538715007391&_rdoc=1&_issn=02775387&md5=86aa1305f87acdbe534d1e611e01140c">class="imgLazyJSB inlineImage" height="16" width="11" alt="View the MathML source" title="View the MathML source" src="/sd/grey_pxl.gif" data-inlimgeid="1-s2.0-S0277538715007391-si1.gif">class="mathContainer hidden">class="mathCode">$\overline{6}$ or P6₃/m, bear on the associated point symmetry groups, which describe the local site symmetry of the dopant Ln ions. This paper aims at resolving this controversy. For this purpose two approaches are utilized. First, several new samples were synthesized and characterized by photoluminescence (PL) spectroscopy. Both the emission and excitation PL spectra have been measured. The analysis of the present experimental data indicates unequivocally that the dopant Ln³⁺ ions enter the crystal lattice β-NaGF₄ and β-NaYF₄ at two crystallographically distinct sites. Hence, the correct space group for these hosts is P  class="mathmlsrc">title="View the MathML source" class="mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0277538715007391&_mathId=si1.gif&_user=111111111&_pii=S0277538715007391&_rdoc=1&_issn=02775387&md5=86aa1305f87acdbe534d1e611e01140c">class="imgLazyJSB inlineImage" height="16" width="11" alt="View the MathML source" title="View the MathML source" src="/sd/grey_pxl.gif" data-inlimgeid="1-s2.0-S0277538715007391-si1.gif">class="mathContainer hidden">class="mathCode">$\overline{6}$ and not P6₃/m. The intricacies arising from the sample preparation methods, which bear on the interpretation of the results, are also clarified. Second, the theoretical modeling of the crystal-field parameters (CFPs) is carried out based on superposition model to correlate the available crystallographic and spectroscopic data. The crystal-field analysis enables to ascribe unambiguously the spectroscopically determined sites to the crystallographic sites 1a and 1f. In this way an interpretation of photoluminescence spectra is achieved that fully corroborates the available crystallographic data. The influence of structural disorder occurring in β-NaLnF₄ family of compounds on the ⁵D₀ → ⁷F₁ photoluminescence spectra of dopant Eu³⁺ ion and its role in interpretation of experimental data is also discussed.