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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 series of Eu3+/Eu2+ codoped Ca 2 Al 2 SiO 7 were synthesized by traditional solid-state synthesis in reducing atmosphere. In this work, XRD powder diffraction proved that the obtained sample was pure. Photoluminescence properties are characterized by excitation, emission spectra and decay curves. Double center emission is achieved by adjusting excitation wavelength and concentration. Under the 394 nm excitation, the emission spectra Ca 2 Al 2 SiO 7 : Eu phosphors exhibit two bands situated at blue emission of 4f5d-4f transition from Eu2+ ion and red emission of 4f-4f transition coming from Eu3+ ion. The red and yellow light can be obtained when the concentration of doped europium ions is at 0.5% and 1%, respectively. When the excitation wavelength was 394, 280 and 584 nm, the emission color change from yellow to blue, respectively. The bond energy theory explains Eu2+ and Eu3+ ion occupy Ca1 site in the Ca 2 Al 2 SiO 7 lattices. In addition, the spectra show that the abnormal intensity peaks of europium ion at 701 nm can be found. Analysis of the related intensity 5D 0 -7F 2 (618 nm) transition peak is similar to that of 5D 0 -7F 4 (701 nm) transition peak in the emission spectra with the Judd-Ofelt theory. [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]

Abstract The existing valence state (Eu2+/Eu3+ and Tb3+/Tb4+) in Eu/Tb ions doped in SrAl 2 Si 2 O 8 were investigated through experimental and theoretical method. Their photoluminescence properties indicated that parts of Eu3+ ions were reduced to Eu2+ in SrAl 2 Si 2 O 8. Based on the bond energy method, the reduction process of the Eu3+→Eu2+ and the preferentially occupancy of Eu3+/Eu2+ in SrAl 2 Si 2 O 8 samples have been discussed. The values of deviation of its bond energy were calculated when Eu ions located at different crystal sites. Theoretical results indicated that the Eu3+ and Eu2+ would preferentially occupy the Sr sites due to the smaller energy variation. In addition, the variation of bond energy of Eu3+(Δ E Eu 3 + - O 2 - Sr =11.367 kcal/mol) is close to Eu2+ (Δ E Eu 2 + - O 2 - Sr = 15.112 kcal/mol), which indicated that the both of Eu2+ and Eu3+can stably exist in SrAl 2 Si 2 O 8 host. When Eu, Tb ions are co-doped in SrAl 2 Si 2 O 8 , the photoluminescence shows that only the characteristic emission peaks of Eu2+ and Eu3+ can be found and the emission of Tb3+ disappeared. It is suggested that the Tb3+ is oxidized to Tb4+ and the Eu3+ is reduced to Eu2+. Compared with Eu ion, the variation of bond energy for Tb3+(Δ E Tb 3 + - O 2 - Sr =10.084 kcal/mol) is more closer to Tb4+ (Δ E Tb 4 + - O 2 - Sr =9.628 kcal/mol), so in Tb3+, Eu3+ co-doped in SrAl 2 Si 2 O 8 , the Tb4+ ion has the highest priority to occupy the Sr sites, Tb3+ loses one electron to form the tetravalent Tb4+, and the excess electrons are transferred to the surrounding neighboring Eu3+ site, Eu3+ gets an electron and is reduced to Eu2+. The theoretical results are in accord with the experimental measurement. Highlights • Eu/Tb doped in SrAl 2 Si 2 O 8 were synthesized by high-temperature solid state method. • Rietveld refinement result demonstrate that Eu2+/3+, Tb3+/4+ ions occupy the Sr site. • Eu3+ can be reduced to Eu2+ and Tb3+ can be oxidized by Eu3+ in SrAl 2 Si 2 O 8 at air. • Calculation results of bond energy method prove Eu2+/3+, Tb3+/4+ occupy the Sr site. [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]