Results of spectroscopic measurements of YPO 4 :Pr 3 + are reported. Based on these results, the fluorescent lines were identified. It is confirmed that the 612.8 nm emission line is due to 1 D 2 (Γ 3 )-> 3 H 4 (Γ 5 ) transition of Pr 3 + . It is found that the fluorescence lines from 1 D 2 are dominant for samples of low Pr 3 + concentration when 3 P 0 is selectively excited, which indicated very efficient relaxation from 3 P 0 to 1 D 2 .