The photonic band gap(PBG) structures of four types of annular photonic crystals(PCs) with inner-scatter of rectangular,square,hexagonal and circle shapes are respectively calculated by the plane wave expansion method.The optimal samples with the largest gap-midgap ratio for each structure are obtained by scanning the four parameters:filling ratio f,dielectric constant ε1,rotating angle θ of inner-scatters and outside radius R of the air ring.The results show that the band gap can be further maximized by adjusting the structural parameters,and a wide PBG with the gap-midgap ratio of 20.4% is gained in the annular photonic crystal with rectangular inner-scatters.
A white long-lasting phosphor Ca2MgSi2O7:Dy3+ was prepared by the solid-state reaction. A strong band peaked at 260 nm was shown in the excitation spectrum of 578 nm emission, which might be attributed to the oxygen deficiency of the host. After irradiated with 254 nm for 4 min, the white afterglow of the sample could be seen for 3 h. Moreover, the depths and frequency factors of trap centers were calculated from the thermo-luminescence curve of the sample, which indicated that the trap centers corresponding to the 414 K band were more helpful to the long-lasting phosphorescence.
