Papers by Author: Hom Nath Luitel

Abstract: Calcium silicate phosphors, Ca2-xSiO4(CS):Eu3+x, CS:Eu2+x and Ca2-y-zMgSi2O7 (CMS):Eu2+y,Dy3+z were prepared by the solid state reaction. The phases in CS:Eu3+ system were β- and αL’ -types. The fluorescent color under a black-light irradiation was red and the emission spectrum consisted of 590nm(αL’), 615nm(β) and 625nm(αL’) peaks. The emission intensity took a maximum value at x=0.2. The addition of B3+ accelerated the solid solution of Eu3+. The phase in CS:Eu2+ system was β-type only. The fluorescent color was yellow-green(520nm). The emission intensity took a maximum value at x=0.01. The CMS product showed the akermanite phase. The lattice constants of CMS:Eu2+ increased with increasing Eu content, but those became constant at y>0.05. The fluorescent color of CMS:Eu2+ was yellow-green and the emission intensity took a maximum value at y=0.03. In the case of CMS:Eu2+0.03,Dy3+z, the fluorescent color and the afterglow color were same, yellow-green. The emission intensity took a maximum value at z=0.06. The longest afterglow time, 23min., was obtained at z=0.09. The trap depth were 0.64-0.69 eV.

Abstract: Sr4Al14O25:Eu2+, Dy3+ long persistent phosphors with different B, Eu and Dy contents were prepared by solid phase reaction at various temperatures in H2/N2=1/9 atmosphere. X- ray diffraction and scanning electron microscopy observations showed that, when the phosphor was doped with 40 at% B, single dense Sr4Al14O25 phase was formed but for the samples with less than 40 at% B, mixed phases containing SrAl12O19 and SrAl2O4 were observed while for higher B content (100 at%) SrAl2B2O7 phases appeared. The phosphor showed emission peak centered at 500 nm with blue green color. When 40 at% of H3BO3 was added and doped with 4 at% of Eu and 8 at% of Dy, it showed the maximum initial intensity of 3170 mcd.m-2 and the longest persistency which is greater than 20 h over value of 5 mcd.m-2.