SrAl_2O_4∶Eu^(2+),Nd^(3+) and Dy^(3+) Long Afterglow Phosphor

The SrAl 2O 4∶Eu 2+ , Nd 3+ and SrAl 2O 4∶Eu 2+ , Dy 3+ long afterglow phosphor were synthesized. Their excitation and emission spectra at different excitation and afterglow characteristics were analyzed after the excitation power was taken off. The effects of Eu 2+ , Dy 3+ , Nd 3+ mole concentrations on phosphorescence characteristics were also discussed. It is crucial to have trapping levels located at a suitable depth related to the thermal release rate at room temperature. The incorporation of Nd 3+ ions as an auxiliary activator into the SrAl 2O 4∶Eu 2+ system causes very intense and long phosphorescence. The response time of SrAl 2O 4∶Eu 2+ , Dy 3+ phosphors is quicker than that of SrAl 2O 4∶Eu 2+ , Nd 3+ . Phosphorescence characteristics of SrAl 2O 4∶Eu 2+, Nd 3+ is much better than those of SrAl 2O 4∶Eu 2+ , Dy 3+ . The integrate area of the excitation spectrum of SrAl 2O 4∶Eu 2+ , Nd 3+ phosphor is larger than that of SrAl 2O 4∶Eu 2+ , Dy 3+ phosphor within the range of 250～360 nm. For phosphorescence characteristics to the system of SrAl 2O 4∶Eu 2+ , Nd 3+ phosphor, the optimum concentration of Nd 3+ trivalent rare earth ions is 0.05 mol.

Negative-Resistance Characteristics Analysis of Poly-Silicon Resistors Formed on the Flow Sensor

In this paper we put forward a new concept about effective trapping center concentration N^e_T which is decreasing with the trapped charge Q corresponding to index movement,based on that,we discuss theⅠ-Ⅴand temperature characteristics of polysilicon resistors.The new concept presents ideal theoretical interpretion for the originally observed current-voltage negative-resistance characteristics of polysilicon resistors formed on the flow sensor,and also for poly-silicon film resistors. The final results agree well with the theoretical current-voltage characteristics.

Studies on long lasting optical properties of Eu^(2+) and Dy^(3+) doped di-barium magnesium silicate phosphors

Di-barium magnesium silicate phosphors doped with europium and dysprosium were prepared under a weak reducing atmosphere.X-ray diffraction pattern of the sample was also done that confirmed the proper preparation of the phosphor.Scanning electron microscope（SEM） images confirmed that the sample has regular surface and uniform grain size distribution.Comparative studies of phosphorescence decay of Ba2MgSi2O7：Eu^2＋,Dy^3＋ phosphors with different concentration of Dy^3＋ were done.The phosphor with 0.5/1.5 mol%of Eu/Dy,exhibited optimum green color afterglow properties.This emission is expected to arise due to transition of Eu^2＋ ions from any of the sublevels of 4f^65d^1 configuration to ^8S（7/2） level of the 4f7 configuration.For a suitable trap depth,the trap concentration is expected to be proportional to the concentration of Dy^3＋.These traps are responsible for holding the charge career for a reasonable time,subsequently for increasing the time of afterglow.Hence,optimum Dy3＊ concentration produces the longer afterglow duration with higher intensity of luminescence signals.Trap depth were also calculated using thermoluminescence glow curve which was indicative of formation of traps suitable for long afterglow.