采用两步高温热分解法合成了纳米异质结构的NaYF4∶Yb3+,Tm3+/CdSe。X射线衍射测试结果表明样品由纯六角相的NaYF4(β-NaYF4)和纤锌矿型CdSe组成。980 nm激发的上转换光谱表明NaYF4∶Yb3+,Tm3+和CdSe之间存在能量传递, Tm3+将Yb3+ 传递给它的能量部分地传递给CdSe, 被激发的CdSe又将能量回传给Tm3+的相应能级, 最终使得NaYF4∶Yb3+,Tm3+的紫外和蓝光发射完全消失, 而797 nm的近红外发射大幅增强。NaYF4∶Yb3+,Tm3+/CdSe纳米异质结构的激发光和发射光均处于生物组织的光学透过窗口(700～1 100 nm), 对生物组织的光损伤小, 在生物医学领域有很大的应用潜力。

NaYF4∶Yb3+,Tm3+/CdSe nanoheterostructures with NIR-to-NIR upconversion luminescence were synthesized by a two-step improved wet-chemical method. X-ray diffraction (XRD) characterization shows that the nanoheterostructures are composed of both pure hexagonal phase NaYF4∶Yb3+,Tm3+ and wurtzite phase CdSe. Upconversion emission spectra under the excitation of 980 nm near-infrared laser show that 797 nm emission from Tm3+ ions has been enhanced greatly, while neither ultraviolet nor blue emissions of Tm3+ appear compared with that of pure NaYF4∶Yb3+,Tm3+. It indicates that the energy transfer occurs between NaYF4∶Yb3+,Tm3+ and CdSe. Under 980 nm excitation, the energy absorbed by Yb3+ ions transfers to Tm3+ ions, then transfers to CdSe partially, and finally the excited CdSe returns the energy back to the corresponding energy levels of Tm3+. These processes lead to the quenching of UV and blue emissions and the enhancement of 797 nm emission of Tm3+ ions in the NaYF4∶Yb3+,Tm3+/CdSe nanoheterostructures. The excitation (980 nm) and emission (797 nm) are both located in the NIR spectral range (700-1 100 nm) that is referred as the “optical window” of biological tissues because of the minimum of light scattering and autofluorescence of tissue and a relatively large penetration depth. Therefore, the present NaYF4∶Yb3+,Tm3+/CdSe nanoheterostructures could have potential applications in biology and biomedicine fields.