Influence of intermolecular resonance of fundamental oscillations on the fine structure of luminescence spectra of uranyl compounds

Autor: V. N. Boikov, D. S. Umreiko
Rok vydání: 1993
Předmět:
Zdroj: Journal of Applied Spectroscopy. 58:140-142
ISSN: 1573-8647
0021-9037
DOI: 10.1007/bf00659175
Popis: A previous investigation [1, 2] of the contours of fluorescence spectrum lines of uranyl crystals of an island structure has shown that the broadening of optical transitions on energy sublevels of stretching fully symmetrical vibrations of UO2+ 2 may be explained by the intermolecular resonance (IR) of v1(UO2+2) vibrations of nearby luminescence centers. A successive increase of the vibrational quantum number n of this vibration is appropriate for the gradual isolation of a low-frequency diffuse wing (presumably of a background nature) and the narrowing of the lines. At the same time the Raman scattering (RS) line is narrower by more than one order than the appropriate fluorescence line (FL) even with deduction of the quantity of inhomogeneous broadening of the latter. In this connection, of interest is a comparison of the FL width and location in the crystals of uranyl compounds and in the UO2+2-activated suitable crystalline matrix where IR is, in fact, absent. As such a matrix we have chosen Cs2HfCI 6, possessing the interesting property of high isomorphic solvability of UO2+ 2 ions [3]. As our studies have shown, at low temperatures ( 1%). The absence of doublet splitting of the initial, for luminescence, level (as observed in uranyl crystals) and at the same time the analogy in the structure of the luminescence spectrum with Cs2UO2C14 (Fig. 1) are quite consistent with the notion [3] of isomorphic substitution of octahedral [HfCI6] 2ions in Cs2HfCI 6 crystals for the [UO2C14] 2complexes. The position in the spectrum and half-widths of FL vS(n) and ua(n) corresponding to the transitions to energy sublevels of stretching symmetrical and antisymmetrical vibrations of UO2+2 in Cs2Hft_x(UO2)xC16_2x crystals, x = 0.01, are shown in the Table 1 (the error in determination of vibrational frequencies is 0.3 cm-1). The gradual FL broadening with an increase of n is likely to be attributed to some inhomogeneity of the luminescence centers under consideration [4, 5]: an increase of v 0 in their ensemble is appropriate for a decrease of vl(UO2+2) (in particular, with a decrease of UO2+ 2 concentration to x = 0.0015 the half-widths of v s and lines for n = 0-3 become approximately equal and amount to 0.5 cm 1, while the vibrational frequencies undergo no changes). In this case no wings of the lines typical for uranyl compound crystals have been revealed. It is easily seen that the series of lines represented in the table are described with a sufficient accuracy by the expressions [6]
Databáze: OpenAIRE
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