Controllable optical properties by ratio of Sr/Ca in Sr_(1,97-x)CaMgSi_2O_7 : Eu_(0.01)~(2+) D_(0.02)~(3+) phosphors

摘要

The long afterglow phosphors Sr_(1.97-x)Ca_xMgSi_2O_7 : Eu_(0.01~(2+), Dy_(0.02)~(3+) (x = 0, 0.4, 0.8, 1.2, 1.6, 1.97) were synthesized by the high temperature solid-state reaction method. The phases were analyzed by x-ray powder diffraction. All the samples have a similar structure. A slight shift of the peaks, which implied a change of crystal plane spacing, was found. With a decrease in the Sr/Ca ratio, the crystal plane spacing became smaller. The red shift was found in the emission spectra, from 468 to 529 nm. The 5d level of the Eu2+ ion splits into two sets. With the decrease in the crystal plane spacing, the energy of one set becomes higher while the other one becomes lower. This leads to the red shift of the emission spectra. The afterglow time becomes shorter with the decreasing Sr/Ca ratio. The thermoluminescence curves, which imply the depth of the traps, conform to the various afterglow times of the samples. This is due to the greater ionization potential of the Dy ions with the decreasing crystal plane spacing.