Original Russian Text © S.A. Nemov, A.V. Marchenko, P.P. Seregin, E.A. Tomil'tsev, 2007, published in Fizika i Khimiya Stekla. 658 INTRODUCTION It is known that doping of glasses by transition metals is an effective method for controlling the transparency of these materials. In this respect, the identification of the oxidation states of the transition metal atoms in doped glasses is of obvious interest. In particular, one of these metals is europium. In contrast to the majority of rare-earth metals, europium can be stabilized in two states; therefore, by varying the ratio between the oxidized (Eu 3+ ) and reduced (Eu 2+ ) species, it is possible to control the optical characteristics of the material.It has been established using 151 Eu Mössbauer spectroscopy that, in oxide and fluoride glasses, europium is stabilized in the Eu 3+ state [1][2][3][4][5][6][7][8][9][10][11][12]. In order to obtain the reduced form of europium in a glass, it is necessary to use a strong reducing agent of the AlN type [1,12]. In this paper, it will be demonstrated that the Eu 2+ ions can be stabilized in glasses of the Al 2 O 3 -SiO 2 -MnO-Eu 2 O 3 system without recourse to a reducing agent.
SAMPLE PREPARATION AND EXPERIMENTAL TECHNIQUEThe glass was synthesized from a mixture of the composition (mol %) 19.5Al 2 O 3 , 31.5SiO 2 , 26.5MnO, and 22.5Eu 2 O 3 in zirconium crucibles in a nitrogen atmosphere at a temperature of 1573 K. The choice of the composition of the glass was motivated by the necessity of attaining the highest solubility of Eu 2 O 3 . All the samples had a characteristic conchoidal fracture and were X-ray amorphous. No microinclusions were revealed in the samples under examination with an infrared microscope.The 151 Eu Mössbauer spectra were recorded on an MS-2201 commercial spectrometer at room temperature with a 151 Sm 2 O 3 source. The surface density of the absorbers with respect to the 151 Eu isotope was equal to 2.5 mg/cm 2 . The linewidth of the EuF 3 absorber with the 151 Sm 2 O 3 source was taken as the instrument linewidth [(3.9 ± 0.2) mm/s]. The isomer shifts are given relative to the spectrum of the Eu 2 O 3 absorber.
RESULTS AND DISCUSSIONThe Mössbauer spectra of the glasses under investigation represent a superposition of two lines, namely, the line with an isomer shift of -(0.65 ± 0.07) mm/s, which corresponds to the Eu 3+ ions, and the line with an isomer shift of -(13.10 ± 0.07) mm/s, which corresponds to the Eu 2+ ions (figure, curve a ). When we replaced Al 2 O 3 in the initial mixture by the corresponding amount of AlN, the material obtained after calcining of this mixture at a temperature of 1573 K turned out to be polycrystalline and the 151 Eu Mössbauer spectrum in this case corresponded to the presence of Eu 2+ ions alone (figure, curve b ).It is worth noting that the synthesis of glasses in the Al 2 O 3 -SiO 2 -MnO-Eu 2 O 3 system in a nitrogen atmosphere makes it possible to stabilize ~25% Eu in the reduced form in the structural network of the glass. The reduction of Eu 3+ to Eu 2+ can p...
