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The synthesis and photo-luminescence properties of Eu2+/Eu3+ or Ce3+/Eu3+ co-doped Sr 5 (BO 3) 3 F compounds are reported. Using the Sr 5 (BO 3) 3 F as the host, through the solid state reaction under the reductive atmosphere, Eu2+/Eu3+ and Ce3+/Eu3+co-doped samples were prepared. These compounds exhibit good photo-luminescence properties. Under the excitation of 376 nm, an unusual red orange emission coming from the Eu2+ ions can be obtained in Eu ions doped Sr 5 (BO 3) 3 F, which exhibits a broadband emission in the range of 450–800 nm with the peak at around 600 nm. At the same time, the characteristic f-f excitation and emission of Eu3+ can improve and adjust the Eu2+ emission in Eu3+/Eu2+ codoped Sr 5 (BO 3) 3 F. In addition, the adjustable luminescence properties from blue to white of Sr 5 (BO 3) 3 F:Ce3+, Eu3+ are investigated. The energy transfer behavior from Ce3+ to Eu3+ was confirmed. In the spectra of the co-doped samples, we can hardly observe the characteristic peak of Eu2+, because Ce4+ can oxidize Eu2+ to Eu3+, and Ce4+ itself is reduced to Ce3+. The CIE coordinates from (0.2758, 0.2420) to (0.3857, 0.3015) show Sr 5 (BO 3) 3 F:3%Ce3+, x%Eu3+ (x = 1,3,5,7,9) are in the white light emission region. All results demonstrate that the Sr 5 (BO 3) 3 F:Eu3+/Eu2+ and Sr 5 (BO 3) 3 F:Ce3+/Eu3+ phosphors have good application prospects for LED plant growth and white LED, respectively. The bond energy method was used to explain the reason why the Eu2+/Eu3+ ion instead of only Eu2+ and Ce3+/Eu3+ instead of Ce3+/Eu3+/Eu2+ can exist in the host Sr 5 (BO 3) 3 F. The theoretical analysis agree well with the experimental result. [ABSTRACT FROM AUTHOR]

A novel luminescent material Sr 5 (BO 3) 3 F:x%Eu3+ was synthesized for the first time by a high temperature solid phase reaction in an air atmosphere. The luminescence properties and site occupancy of Sr 5 (BO 3) 3 F:x%Eu3+ phosphors were studied. The XRD powder diffraction data imply that the series of targets synthesized are pure phases. After repeated experiments, it was found that the main peak position of the excitation and emission spectra changed greatly when the same concentration or different concentration of Eu3+ was doped, and two kinds of spectral phenomena appeared. First, the position of the broadband excitation peak is about 335 nm, and the position of the strongest emission peak belongs to the 5D 0 →7F 0 transition of Eu3+ at 572 nm. Second, the position of the broadband excitation peak is about 275 nm, and the position of the strongest emission peak belongs to the 5D 0 →7F 2 transition of Eu3+ at 619 nm. These imply that different lattice sites are occupied by Eu3+ in Sr 5 (BO 3) 3 F. At the same time, the unusually strong 5D 0 →7F 0 transition illustrates the presence of interstitial oxygen and anomalous crystal field strength in system. A theoretical calculation method of bond energy was applied to study the site occupancy of Eu3+, which shows that any one of Sr1, Sr2, and Sr3 has the possibility of being occupied by Eu3+. Therefore, our test results are consistent well with the theoretical analysis. [ABSTRACT FROM AUTHOR]

Eu-doped MAlSi 2 O 6 (M = Li, Na, K, Rb, Cs) phosphors were synthesized by solid-state reaction in air. The crystal structure and optical properties of the phosphors were investigated by X-ray powder diffraction and photoluminescence. Their emission spectra are composed of some broad bands coming from the 5d-4f transition of Eu 2+ and some sharp emission peaks coming from the f-f transitions of Eu 3+ . The co-existence of Eu 3+ and Eu 2+ cations is detected in MAlSi 2 O 6 :2%Eu, which shows that the unusual Eu 3+ →Eu 2+ reduction process occurs in MAlSi 2 O 6 . The preferential occupancy of Eu 3+ or Eu 2+ in MAlSi 2 O 6 can be calculated to be M + sites by the bond-energy method. The deviation of the Eu 3+ –O 2- bond energy is closed to that of the Eu 2+ –O 2- bond energy, which means that Eu 3+ and Eu 2+ can coexist in air. The abnormal reduction of Eu 3+ to Eu 2+ can be explained by charge compensation model. The doped Eu 3+ was induced to M + and the vacancy ( V M ) may be formed. The vacancy( V M ) acted as a donor of electrons, and the Eu M ∙ ∙ defect acted as an acceptor of electrons. The theoretical result is consistent with the experimental phenomenon. [ABSTRACT FROM AUTHOR]

A bond-energy method is used to determine the site occupancy preference of Eu 3+ or Eu 2+ and further firstly extended to study the spontaneous reduction of Eu 3+ doped CaAl 2 Si 2 O 8 based on the bond valence model. The phosphor CaAl 2 Si 2 O 8 : Eu was synthesized under air condition. The co-existence of Eu 3+ and Eu 2+ cations was detected through photoluminescence measurement. The occupancy of Eu 3+ or Eu 2+ in CaAl 2 Si 2 O 8 can be determined by comparing the deviation of its bond energy in different locations at Ca 2+ , Si 4+ and Al 3+ sites. Theoretical calculation result indicates that the Eu 3+ and Eu 2+ would preferentially occupy the smaller energy variation sites Ca4, which can be assigned to Eu4 site. The more important result is that the energy variation of Eu 2+ at Eu4 sites is smaller than that of Eu 3+ at the same sites, which indicates that Eu 2+ is more stable than Eu 3+ at Eu4 sites, so the spontaneous Eu 3+ →Eu 2+ reduction can be found in the CaAl 2 Si 2 O 8 . The same bond energy method can be extended to explain the reason why the Sm 3+ doped CaAl 2 Si 2 O 8 can't be reduced into Sm 2+ under reduction condition. The theoretical result is consistent with the experimental phenomenon. This should help us to have a further understanding of spontaneous Eu 3+ →Eu 2+ reduction in the inorganic material. [ABSTRACT FROM AUTHOR]