Single crystals of SrAl2O4:Eu2+, Dy3+ with extremely strong afterglow were investigated with photoconductivity experiments. The photocurrent excitation spectra were measured at 80 and 300 K and compared with photoluminescence excitation spectra. Experiments on single crystals without doping Dy3+ were also performed for comparison. The results are found to support a hole-trapping model which has been used to explain the strong afterglow from this material.