Probing Site Symmetry Around Eu³⁺ in Nanocrystalline ThO₂ Using Time Resolved Emission Spectroscopy

Abstract

ThO 2 :Eu 3+ nanoparticles were synthesized at 300°C by combustion route using urea as a fuel and characterized by thermogravimetric/differential thermal analysis, X-ray diffraction, transmission electron microscopy, and photoluminescence techniques. To investigate the effect of annealing temperature, as synthesized powder were heated further at 500°C, 700°C, and 900°C. It was observed that extent of asymmetry around Eu 3+ at 700°C/900°C is very high as compared to as-prepared or 500°C annealed sample. Based on the time resolved emission spectroscopic investigations, it was inferred that two different types of Eu 3+ ions were present in the ThO 2 nanoparticles. In ThO 2 structure, Eu 3+ ions occupy two sites; cubic (O h ) and noncubic (<C 2v ) as can be confirmed from our emission studies. Short-lived species T 1 (~1.3-3.4 ms) predominates at higher annealing temperature arises because of Eu 3+ ions occupying noncubic (<C 2v ) sites without inversion symmetry, whereas long-lived species T 2 (~4.6-6.6 ms) can be ascribed to Eu 3+ ions occupying cubic sites (O h ) with inversion symmetry.

Optical properties of Eu 3+ activated thorium molybdate and thorium tungstate: Structure, local symmetry and photophysical properties

“…So it can be inferred from these discussions that local symmetry for Eu 3+ ion in of Th(MoO 4 ) 2 and Th(WO 4 ) 2 is orthorhombic with point group C 3v . Similar phenomenon for europium ion has been observed in case of nanocrystalline thoria where site symmetry is reduced to less than C 2v [32].…”

“…The symmetry around the Eu 3+ ion can thus be obtained from the shape of the emission spectrum. We have extensively used Eu 3+ as a structural probe in variety of hosts to decipher the structural and symmetry related information [15][16][17][18][19]. [21].…”

Interpretation of europium(III) spectra

“…By site selective excitation and application of the selection rules, sites with O h and C 3v symmetry could be identified in ThO 2 :Eu 3+ crystals [657]. These two types of sites in ThO 2 :Eu 3+ have also been detected by time-resolved luminescence spectroscopy [658]. The luminescence spectra of Eu 3+ have been used to monitor the devitrification process of a fluorozirconate glass to a glass ceramic [659].…”

An efficient gel-combustion synthesis of visible light emitting barium zirconate perovskite nanoceramics: Probing the photoluminescence of Sm 3+ and Eu 3+ doped BaZrO 3

“…Moreover, the 5 D 0 -7 F 0 transition is only allowed in the following 10 site symmetries: C s , C 1 , C 2 , C 3 , C 4 , C 6 , C 2V , C 3V , C 4V , and C 6V , according to the ED selection rule [43].…”

“…We wanted to the probe the site occupancy of Eu 3 þ and Sm 3 þ through time resolved photoluminescence spectroscopy. Eu 3 þ is often used as a structural probe [41][42][43][44][45][46][47], because of the (a) relative simplicity of its energy-level structure and the fact that it possesses non-degenerate ground ( 7 F 0 ) and excited ( 5 D 0 ) states and (b) absorption and emission spectra of this ion show marked dependence on its site symmetry in the host material.The orange emission (590-600 nm) of Eu 3 þ due to the magnetic dipole transition (MDT) 5 D 0 -7 F 1 is not affected much by the site symmetry, because they are parity-allowed, while the red emission ( $ 610-630 nm) due to the electric dipole transition (EDT) of 5 D 0 -7 F 2 , being hypersensitive, is affected by the site symmetry of Eu 3 þ ion. In a crystal site inversion symmetry the EDT are strictly forbidden and the MDT are usually the dominant emission line.…”