phosphors content, the afterglow decay curve of samples consists of the initial fast decay phase and the subsequent slow decay phase. So we applied a double exponential decay function to fit the afterglow curve[11–13], and the fit- ted equation is as follows:
01 2
12 ( ) exp exp tt I t I I I τ τ = + + ⎛ ⎞ ⎛ ⎞ −− ⎜ ⎟ ⎜ ⎟ ⎝ ⎠ ⎝ ⎠ (1) where I(t) is the afterglow intensity at time t; I0 is the correction value of fitting; I1 and I2 are the initial inten- sity of afterglow at fast and slow decay phase; τ1 and τ2 are the time needed when the afterglow at fast, slow de- cay phase decays to 1/e of initial intensity, respectively. The fitting value of the parameters of I1, I2, τ1, τ2 and the correlation coefficient between the fitted values and the experimental values are listed in Table 2, and the fitting curves of SMSED and luminescent fiber containing SMSED of 15 wt.% are shown in Fig. 6. The data in the Table 2 show that: (1) Double expo- nential function can fit the afterglow decay curve of the samples well, and the correlation between each fitting data and experimental value was greater than 99.8%; (2) The afterglow initial intensity of fast decay phase was much higher than that of slow decay phase, but the after- glow life of slow decay phase was significantly longer than that of fast decay phase; (3) The afterglow initial intensity in fast and slow decay phases, that is, I1 and I2 value decreased significantly along with the decrease of the content of SMSED phosphors in the luminescent fi- bers, i.e. a positive correlation exists. However there was no trend change in the decay time for the various