LiXun Yang

Optimization mechanism of CaSi2O2N2 : Eu2+ phosphor by La3+ ion doping

La3+(lanthanide 3+) ion doping may significantly improve the photoluminescence properties of CaSi2O2N2 : Eu2+, a potential yellow–green phosphor for ultraviolet or blue light-emitting diodes. The optimization mechanism was studied in detail by the case of La3+ doping. The La3+ ions could stabilize Ca2+ vacancies, inhibit the oxidization of Eu2+ to Eu3+, based on x-ray photoelectron spectroscopy, x-ray absorption near-edge structure measurements and first-principles calculations. Consequently, not only could the total number of activators be increased, but also the non-radiative transition probability between Eu2+ and Eu3+ could be reduced as a result of La3+ doping. It was also observed that the photoluminescence of CaSi2O2N2 : Eu2+ phosphors could be enhanced by the addition of many La3+ ions, but not Sm3+ and Yb3+ ions, which confirmed the mechanism.

Growth and structure of BiSrYCeCuO T∗-phase single crystals

The first T∗-phase single crystals with the composition Bi0.73Sr0.49Y1.20Ce0.88Cu2.14Ox were grown by a flux method. The size of the largest crystals obtained was 1.5 × 1.5 × 0.3 mm3. The morphology of the crystals was observed with a scanning electron microscope. Both the X-ray diffraction and electron diffraction results indicate that the as-grown crystals have a tetragonal structure with a = 3.799 A and c = 12.479 A.