In the last decades

much attention has been paid to the Er

3+

doped glass materials since it is widely known that the transition

4

I

13/2

→

4

I

15/2

of Er

3+

can give an emission peaking around 1.5 μm

which matches the IR optical communication window.To our knowledge there are very few of investigations on the dynamics of 1.5μm emission of Er

3+

. The transfer function theory is introduced to investigate transient fluorescent behavior of the transition

4

I

13/2

→

4

I

15/2

in the Er

3+

doped materials under 980 nm-pulsed excitation. A mathematical expression for the temporal emission evolution is given. It is found that after having been excited by 980 nm δ-pulse the luminescence decay of level

4

I

13/2

obeys double exponential function law

and the variation of population of the level

4

I

13/2

has two stages: rise-stage and set-stage.