Spectroscopic studies of the up-conversion excitation of the blue P-3(
0) emission using two near-infrared photons in Pr3+ doped yttrium alum
inum garnet and LiYF4 crystals are reported. The excitation spectra an
d decay time measurements indicate the sequential absorption of two ph
otons with the nonresonant first step. Two-photon excitation spectra r
evealed a structure not seen in one-photon measurements, allowing iden
tification of several I-1(6) Stark levels.