Phosphorescence of beta irradiated Sr 4 Al 14 O 25:Eu 2+,Dy 3+― A persistent luminescence phosphor

Phosphorescence of beta irradiated Sr 4 Al 14 O 25 :Eu 2+ ,Dy 3+ has been analysed. The persistent luminescence that defines this phosphor is phosphorescence hence the justification for this study. A set of phosphorescence decay curves were measured at various temperatures T ph between 20 and 352 degrees C following irradiation to 2 Gy. The residual thermoluminescence (R -TL) was recorded at 1 degrees C/s after the phosphorescence decay. A conventional TL glow curve recorded at the same rate following irradiation to 2 Gy produces two composite glow peaks P1 and P2 at 63 and 252 degrees C respectively. The decay curves measured between T ph = 28 - 60 degrees C and 200 - 240 degrees C associated with peaks P1 and P2 respectively give the values of the activation energy of peaks P1 and P2 as 0.59 +/- 0.01 and 0.80 +/- 0.04 eV. The effective frequency factors associated with the traps are 6.2 x 10 9 and 6.4 x 10 5 s -1 respectively. Peaks P1 and P2 are affected by thermal quenching with activation energy W = 0.69 +/- 0.06 eV and 0.66 +/- 0.03 eV respectively. The R -TL glow curves show two maxima R1 and R2 at -72 and 260 degrees C respectively. Kinetic analysis of R -TL peak R2 shows a Gaussian distribution of trap energy whereas the same analysis on R -TL peak R1 shows a non -Gaussian distribution of trap energy. The mean values of activation energy corresponding to the respective electron traps of R1 and R2 are estimated to be 0.62 +/- 0.07 and 1.04 +/- 0.06 eV. For peak R2, the Gaussian distribution curve shows the maximum at -1.06 eV which indicates that most electron traps corresponding to peak R2 have this trap depth.