Lanthanide-doped β-NaYF4 nanomaterials have attracted intense attention for their narrow emission linewidth and very weak background emission without autofluorescence in recent years,whereas β-NaYF4∶Yb3+,Tm3+ intensive ultraviolet and blue emissions can be absorbed by biological tissues causing photodamage.Here NIR-to-NIR up-conversion florescent NaYF4∶Yb3+,Tm3+/CdSe nanoheterostructures were synthesized.The X-ray diffraction(XRD)shows that the nanoheterostructures are composed of both pure hexagonal phase NaYF4∶Yb3+,Tm3+ and wurtzite phase CdSe.Under 980 nm near-infrared laser excitation,the samples showed that NIR(797 nm)emissions of NaYF4∶Yb3+,Tm3+ were enhanced greatly,while neither ultraviolet nor blue emissions appeared and no any peaks of CdSe were observed.It strongly proved that exists F(o)rster resonance energy transfer(FRET)between NaYF4 nanoparticles of up-conversion lanthanide phosphor and CdSe quantum dots.In the nanoheterostructures,980 nm photon was absorbed by Yb3+,then passed the energy to Tm3+,following CdSe absorbed the energy comes from NaYF4 without any emissions itself,but acted as acceptors to mediate energy transfer backward to NaYF4.This maybe the reasons why ultraviolet and blue emissions were attenuated and CdSe did not give any detectable fluorescence.Due to the excitation(980 nm)and emission(797 nm)of the nanoheterostructures were both in the range of the NIR spectral range(700-1,200 nm)which were referred as the “ optical window ” of the biological tissues because of the minimum of scattering,autofluorescence and a intenser penetrate depth,the NaYF4∶Yb3+,Tm3+/CdSe nanoheterostructures woud show potential applications in vivo optical biological imaging field.