Nd3+ doped alpha-NaYF4 nanocrystals with size of about 15 nm were successfully synthesized through hydrothermal method. Nearly pure near-infrared to near-infrared (NIR-to-NIR) luminescence can be realized. Moreover, the excitation and the emission at 880 and 1060 nm, respectively, are away from the visible region. These are beneficial to deeper tissue penetration and reduced auto-fluorescence. This material exhibits an excellent NIR-to-NIR emission performance and is thus potentially applicable as a high-contrast in vitro and in vivo imaging probe.