Song Zhen

Photoluminescence properties of Ce3+ and Mn2+-activated Ba9Sc2Si6O24 phosphor for white light emitting diodes

A single-phased silicate compound (Ba1−xCex)9(Sc1−yMny)2Si6O24 was prepared by solid-state reaction at high temperature. From powder X-ray diffraction (XRD) analysis, the formation of Ba9Sc2Si6O24 with an R3 space group was confirmed. In the photoluminescence spectra under ultraviolet (UV) ray excitation, the Ba9Sc2Si6O24:Ce3+, Mn2+ phosphor emits two distinctive color light bands: a blue one originating from Ce3+ and a red one caused by Mn2+. The energy transfer process from Ce3+ to Mn2+ was confirmed, the critical radius as well as the transfer efficiency was calculated, and the energy transfer mechanism was discussed. In addition, the decay-time testing indicates that the energy transfer efficiencies from Ce(1) to Mn2+ and Ce(2) to Mn2+ are different. The emission chromaticity of Ba9Sc2Si6O24:Ce3+, Mn2+ phosphor could be tuned from blue to red by altering the Ce3+/Mn2+ concentration ratio.

Solid solubility and photoluminescence of Y3Al5O12:Ce3= prepared by using (Y1−xCex)2O3 as precursor

Trivalent cerium-doped yttrium aluminum garnet (YAG:Ce3=) phosphors are synthesized by solid-state reaction method through using (Y1−xCex)2O3 solid solutions as precursors. Solid solubility limits of Ce3= replacing Y3= in Y2O3 and YAG are determined to be 40% and 7.5%, respectively, based on the relationship between the lattice parameter and chemical composition. Using (Y1−xCex)2O3 as precursors we synthesize YAG:Ce3= single phase at 1450 °C and N2 atmosphere. However, under the same conditions using CeO2 there exists a second phase YAlO3 as impurity. The photoluminescence intensity of YAG:Ce3= increases monotonically with the increase of Ce concentration until it reaches a maximum at solid solubility limits of Ce3= in YAG.

Complementary method to locate atomic coordinates by combined searching method of structure-sensitive indexes based on bond valence method*

Bond valence method illustrates the relation between valence and length of a particular bond type. This theory has been used to predict structure information, but the effect is very limited. In this paper, two indexes, i.e., global instability index (GII) and bond strain index (BSI), are adopted as a judgment of a search-match program for prediction. The results show that with GII and BSI combined as judgment, the predicted atom positions are very close to real ones. The mechanism and validity of this searching program are also discussed. The GII & BSI distribution contour map reveals that the predicted function is a reflection of exponential feature of bond valence formula. This combined searching method may be integrated with other structure-determination method, and may be helpful in refining and testifying light atom positions.