Fluorescence lifetime of Nd3+4F3/2 state in NdP5O14 crystals at room temperature was in- vestigated.Fluorescence two-exponential decay which limits the optical gain of NdP5O14 at high excitation intensity was observed.The phenomenon is analyzed theoretically with en- ergy transfer process.A τ-meter for selected pumping of a pulsed rh-6G laser is briefly described.