A fiber-optic thermometer is developed based on the temperature dependence of the afterglow phosphorescence intensity which is dominated by the thermal excitation of trapped carriers using long duration phosphor, SrAl2O4 :Eu2+,Dy3+. The intensity of afterglow phosphorescence from the long phosphorescent sensor head increases greatly and linearly with the temperature ranging from 270 to 320 K with the temperature coefficient of 1.3 % K-1. The long phosphorescent materials are potentially useful phosphors for the sensitive sensor head in fiber-optic thermometers. (C) 2002 The Electrochemical Society.