Yueliang Zhou

All-optical switching in subwavelength metallic grating structure containing nonlinear optical materials

All-optical switching based on a subwavelength metallic grating structure containing nonlinear optical materials has been proposed and numerically investigated. Metal-dielectric composite material is used in the switching for its larger third-order nonlinear susceptibility (approximately 10(-7)esu) and ultrafast response properties. The calculated dependence of the signal light intensity on the pump light intensity shows a bistable behavior, which results in a significant switch effect. It rests on a surface plasmons enhanced intensity-dependent change of the effective dielectric constant of Kerr nonlinear media, corresponding to a transition of the far-field transmission from a low- to high-transmission state. The study of this switching structure shows great advantages of smaller size, lower requirement of pump light intensity, and shorter switching time at approximately the picosecond level.

Preparation of Y3Al5O12:Eu phosphors by citric-gel method and their luminescent properties

Abstract By using metal nitrates as starting materials and citric acid as complexing agent, Y3Al5O12 (YAG) and Y3Al5O12:Eu (1 mol%) (YAG:Eu) powder phosphors were prepared by a citrate–gel method. The formation process of YAG and YAG:Eu were investigated by means of XRD, TG–DTA and FT-IR spectra. The purified crystalline phases of YAG and YAG:Eu were obtained at 800 °C. The crystalline YAG:Eu phosphors showed an orange–red emission with 5 D 0 – 7 F 1 (591 nm) as the most prominent group, whose intensity was dependent on the pH value of the starting solution, citric acid content and firing temperature. It has been found that the suitable pH and citric acid/metal ratio are 3 and 2 for obtaining the highest emission intensity, respectively. The emission intensity increases steadily with increasing the annealing temperature from 800 to 1200 °C, and nearly remains constant after 1200 °C. Furthermore, great differences were observed for the lifetimes and the charge transfer band of Eu3+ in crystalline and amorphous states of YAG.

Morphology control and luminescence properties of YAG:Eu phosphors prepared by spray pyrolysis

Starting from nitrate aqueous solutions with citric acid and polyethylene glycol (PEG) as additives, Y3Al5O12:Eu (YAG:Eu) phosphors were prepared by a two-step spray pyrolysis (SP) method. The obtained YAG:Eu phosphor particles have spherical shape, submicron size and smooth surface. The effects of process conditions of the spray pyrolysis on the crystallinity, morphology and luminescence properties of phosphor particles were investigated. The emission intensity of the phosphors increased with increasing of sintering temperature and solution concentration due to the increase of the crystallinity and particles size, respectively. Adequate amount of PEG was necessary for obtaining spherical particles, and the optimum emission intensity could be obtained when the concentration of PEG was 0.10 g/ml in the precursor solution. Compared with the YAG:Eu phosphor prepared by citrate-gel (CG) method with non-spherical morphology, spherical YAG:Eu phosphor particles showed a higher emission intensity.

Citrate–gel synthesis and luminescent properties of ZnGa2O4 doped with Mn2+ and Eu3+

Abstract By using inorganic salts as raw materials and citric acid as complexing agent, spinel oxide ZnGa 2 O 4 and Mn 2+ , Eu 3+ -doped ZnGa 2 O 4 phosphor powders were prepared by a citrate–gel process. X-ray diffraction (XRD), TG–DTA, FT-IR and luminescence excitation and emission spectra were used to characterize the resulting products. The results of XRD reveal that the powders begin to crystallize at 500 °C and pure ZnGa 2 O 4 phase is obtained at 700 °C, which agrees well with the results of TG–DTA and FT-IR. In the crystalline ZnGa 2 O 4 , the Eu 3+ shows its characteristic red (615 nm, 5 D 0 – 7 F 2 ) emission with a quenching concentration of 5 mol% (of Ga 3+ ), and the Mn 2+ shows green emission (505 nm, 4 T 1 – 6 A 1 ) with a quenching concentration of 0.1 mol% (of Zn 2+ ). The luminescence mechanism of ZnGa 2 O 4 :Mn 2+ /Eu 3+ is presented.