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Europium Luminescence as a Structural Probe: Structure‐Dependent Changes in Eu 3+ ‐Substituted Th(C 2 O 4 ) 2 · x H 2 O ( x = 6, 2, and 0)
Author(s) -
Gupta Santosh K.,
Rajeshwari B.,
Achary S. N.,
Patwe S. J.,
Tyagi A. K.,
Natarajan V.,
Kadam R. M.
Publication year - 2015
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201500623
Subject(s) - chemistry , monoclinic crystal system , europium , ion , luminescence , hydrate , analytical chemistry (journal) , crystallography , oxalate , thorium , crystal structure , uranyl , inorganic chemistry , materials science , uranium , optoelectronics , organic chemistry , chromatography , metallurgy
Three different phases of thorium(IV) oxalate hydrate [Th(C 2 O 4 ) 2 · x H 2 O] with different water contents, namely, the hexahydrate, dihydrate, and anhydrous phases, were prepared by thermal treatment of the as‐precipitated hydrated thorium(IV) oxalates. With the change in water content, the structure changes from monoclinic ( C 2/ m ) for the hexahydrate to monoclinic ( C 2/ c ) for the dihydrate and finally to a highly disordered phase for the anhydrous state. The local coordination around the Th 4+ ions in these structures was monitored by using Eu 3+ ions as luminescent probes. The analyses of the emission spectra owing to the electric‐dipole transitions (EDTs) and magnetic‐dipole transitions (MDTs) of the Eu 3+ ions in the different phases revealed that the site symmetry around the Th 4+ ions decreases systematically from symmetric to highly distorted with the decrease in water content. The relative intensity ratios ( I ) of the EDT to MDT for x = 6, 2, and 0 are 2.36, 3.32, and 4.23, respectively. The analyses of the delay curves corresponding to the 5 D 0 level of the Eu 3+ ions indicated biexponential decay with varying lifetimes, which suggests two possible environments around the Eu 3+ ions and a possible role of oxygen vacancies. The long‐lived species is expected to be distant from the charge‐compensation defects, whereas the short‐lived species is nearer to the charge‐compensation defect. Tunability of the emission with the excitation wavelength is observed for all phases and is attributed to the presence of defect‐mediated broad emission in the blue region and red‐orange emission from the Eu 3+ ions.