![]() 30 This byproduct contribute to the formation of strontium vacancies (V Sr), and hence oxygen vacancies (V O), needed for charge neutrality. ![]() 29 The formation of the Sr 3Al 2O 6 byproduct during the synthesis of SrAl 2O 4 has already been observed in previous work. ![]() XRD pattern for sample with x = 1 (Ba ions fully exchanged by Sr ions) showed some additional peaks, which are identified as cubic Sr 3Al 2O 6. With the increase even further of the Sr content, some new peaks were observed in the XRD patterns that can be related to both monoclinic and hexagonal SrAl 2O 4 crystalline phases. All diffraction peaks in Figure 1(a) for x = 0 up to x = 0.6 were visually indexed to the BaAl 2O 4 structure, and no additional peaks belonging to other phases were observed. 27 and 28) and hexagonal (space group P6 3) BaAl 2O 4 (Ref. The XRD patterns were compared to the monoclinic (space group P2 1) and hexagonal (space group P6 322) SrAl 2O 4 (Refs. XRD results obtained for the Ba 1−xSr xAl 2O 4:Eu 3+ ( x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) samples are shown in Figure 1(a). All measurements were performed at room temperature. The same experimental setup has been used successfully in other ternary oxides and fluorides compounds, such as Ca 12Al 14O 33, 23 CdWO 4, 24 BaY 2F 8, 25,26 giving quite interesting results. The incident beam intensity was monitored using an ionization chamber with appropriate gas mixture and pressure, and the number of counts for each incident photon energy was used to normalize the X-ray fluorescence signal, giving the absorption curve, the total XEOL yield, and XEOL emission spectra. A bifurcated optical fibre collected the light generated during the XEOL measurements sending it to the PMT and the spectrometer. The XEOL was measured simultaneously with the X-ray fluorescence using a Hamatsu R 928A PMT and an Ocean Optics HR2000 spectrometer. The usual X-ray absorption measurements were done in fluorescence mode monitoring the area under the Lα 1 and Lα 2 (5849.4 eV, respectively) X-ray fluorescence lines of the Eu dopants. ![]() XEOL experiments were performed in the Brazilian Synchrotron Light Laboratory-LNLS source in Campinas, São Paulo, Brazil, around the Eu L III-edges at the X-ray absorption fine structure (D08B-XAFS-2) beamline (proposal No. A model of the radiation induced luminescence is presented and all these features are discussed in terms of the energetic costs and the type of defects generated in the sample. In Sr-rich samples, the LLP has a slower decay time constant than in Ba-rich samples. X-ray induced long lasting phosphorescence (LLP) was also observed for all samples and it was found that the duration of the phosphorescence emission also depends on the sample composition. The Ba-rich samples are the ones with higher XEOL yield. The saturation level of the XEOL is directly correlated to the amount of damages induced by the irradiation and the sample composition. The XEOL intensities while the sample is under irradiation decreased as a function of the irradiation time, indicating the buildup of radiation damage. Ba 1−xSr xAl 2O 4 samples, with 0 < x < 1, were produced via proteic sol-gel route and it was observed that the XEOL emission spectra are composed by the Eu 2+ and Eu 3+ transitions, although no Eu 2+ was observed in the X-ray absorption spectra. This paper reports the influence of the structural change on the luminescence of Eu-doped barium/strontium aluminates when excited with monochromatic X-rays (also known as X-ray excited optical luminescence-XEOL).
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