Two different upconversion mechanisms leading to green fluorescence in an Er3+doped LiNbO3crystal have been investigated with pulse laser excitations at the wavelengths of 1064 and 980 nm. In the case of the 1064 nm pump, the Er3+ions become excited by the phase‐matched second harmonic wave generated in the LiNbO3crystal, whereas sequential two‐photon absorption is mainly responsible for the excitation with the 980 nm pump. The second harmonic excitation is of an order of magnitude more efficient than the sequential two photon excitation in the upconversion of the near‐infrared pump photons to the green fluorescence. ©1996 American Institute of Physics.