Investigation of the Luminescence of [UO₂X₄]^2– (X = Cl, Br) Complexes in the Organic Phase Using Time-Resolved Laser-Induced Fluorescence Spectroscopy and Quantum Chemical Simulations

Abstract

The luminescence properties of the [UO2Cl4] 2complex in an organic phase, especially the influence of large organic counter cations, have been studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS) and ab initio modeling. The experimental spectrum was assigned by vibronic Franck-Condon calculations on quantum chemical methods based on a combination of relativistic density functional approaches. The shape of the luminescence spectrum of the uranyl tetrachloride complex is determined by symmetrical vibrations and geometrical change upon emission. The possible change of the luminescence properties depending on the first and second uranyl coordination sphere was predicted theoretically for [UO2Br4] 2and [R4N]2[UO2Cl4] ([R4N] = [Bu4N], [A336]) systems. The computations reveal that for U(VI), the second coordination sphere has little influence on the spectrum shape, making speciation of uranyl complexes with identical first coordination-sphere ligands tedious to discriminate. The computed structural changes agreed well with experimental trends; theoretical spectra and peaks attribution are in a good accordance with TRLFS and magnetic circular dichroism (MCD) data respectively.

Influence of the first coordination of uranyl on its luminescence properties: study of uranyl binitrate with N,N-dialkyl amide DEHiBA and water

“…26 The shifts between the ground and excited state stretching frequencies ∆ν s are 65 and 49 cm −1 for the UO 2 (NO 3 ) 2 and UO 2 (NO 3 ) 2 (DEHiBA) 2 , respectively, while the theoretical shifts equal to 90 cm −1 in average. As it has been explained in previous works, 24,25 our theoretical methodology tends to overestimate the vibrational frequencies values; thus we can consider that the agreement between theoretical and experimental data is satisfactory. Moreover, it is difficult to estimate the degree of anharmonicity effects in experimental spectra, which might obviously decrease the band spacings in the higher energy region.…”

Influence of Alkaline Earth Metal Ions on Structures and Luminescent Properties of NamMnUO2(CO3)3(4–m–2n)– (M = Mg, Ca; m, n = 0–2): Time-Resolved Fluorescence Spectroscopy and Ab Initio Studies

“…bonding orbital of the uranium, as observed for the uranyl tetrahalide complexes. 50 As the main objective here is to describe the evolution of the luminescence properties in the series, the methodology appears to be trustworthy.…”

“…TD-DFT has demonstrated its ability to reproduce electronic transitions in uranyl compounds from low-lying excited states, including relativistic effects, electron correlation, and spin-orbit coupling. 49,50 The calculation of the coupling factors between the different vibrational states of the ground and excited states can be achieved using the Franck-Condon approach for dipole-allowed transitions, to finally describe luminescence spectra.…”

Influence of the First Coordination of Uranyl on Its Luminescence Properties: A Study of Uranyl Binitrate with N,N-Dialkyl Amide DEHiBA and Water

“…Moreover, it has been confirmed previously that the 0 → 0 bands in uranium(VI)based complexes are usually more intense compared to the "hot band" intensity at room temperature. 24,65,69 The nature of the bands at 495 and 480 nm in UO 2 (NO 3 ) 2 (H 2 O) 2 and UO 2 (NO 3 ) 2 (DEHiBA) 2 , respectively, remains an open question. Thus we can just suggest that these bands are related to the sample reabsorption, since the luminescence intensity of the band at 480 nm changes depending on the uranium(VI) concentration.…”