Long persistent alkali-earth silicate phosphors doped with Eu~(2+), Nd~(3+)

摘要

Phosphors of Sr_(n)MgSi_(2)O_(5+n)(1 <= n <= 2) singly doped with Eu~(2+) or doubly doped with Eu~(2+) and Nd~(3+) were prepared by using a solid state chemical reaction method. X-ray diffraction spectra revealed that the Sr_(n)MgSi_(2)O_(5+n)(1 <= n <= 2) compounds have the same crystal structure as Sr_(2)MgSi_(2)O_(7). The samples showed a strong blue emission at 470 nm. Their excitation bands are from 250 to 450 nm which were assigned to the 5d-4f transitions of Eu~(2+). Energy transfer between Eu~(2+) ions in inequivalent sites was found. Temperature dependence of photoluminescence was studied. A decrease of luminescence intensity and a blueshift of the emission spectra with increasing temperature were observed in both SrMgSi_(2)O_(6):Eu~(2+) and Sr_(2)MgSi_(2)O_(7):Eu~(2+). Persistent afterglow was detected in the samples. The Eu~(2+) blue afterglow emission could be greatly enhanced by codoping trivalent rare earth ions, such as Nd~(3+). Thermoluminescence measurements revealed that doping with Nd~(3+) created a much large number of traps and hence enhanced the afterglow.