Lanthanide-doped Sr2YF7 nanoparticles: controlled synthesis, optical spectroscopy and biodetection

Sr₂YF₇, as an important matrix for trivalent lanthanide (Ln³⁺) ions to fabricate upconversion (UC) or downshifting (DS) phosphors, has been rarely reported. Herein, monodisperse and size-controllable tetragonal-phase Ln³⁺-doped Sr₂YF₇ nanoparticles (NPs) were synthesized via a facile thermal decomposition method. Upon excitation at 980 nm, UC luminescence properties of Sr₂YF₇:Ln³⁺/Yb³⁺ (Ln = Tm, Er) NPs were systematically surveyed. Particularly, after coating an inert Sr₂YF₇ shell, the UC luminescence intensities of Sr₂YF₇:Tm³⁺/Yb³⁺ and Sr₂YF₇:Er³⁺/Yb³⁺ NPs were enhanced by ~22 and 4 times, respectively. Furthermore, intense multicolor DS luminescence was also achieved in Ce³⁺/Tb³⁺ or Eu³⁺ doped Sr₂YF₇ NPs, with absolute quantum yields of 55.1% (Tb³⁺) and 11.2% (Eu³⁺). The luminescence lifetimes of ⁵D₄ (Tb³⁺) and ⁵D₀ (Eu³⁺) were determined to be 3.7 and 8.1 ms, respectively. By utilizing the long-lived luminescence of Ln³⁺ in these Sr₂YF₇ NPs, we demonstrated their application as sensitive heterogeneous time-resolved photoluminescence bioprobes to detect the protein of avidin and the tumor marker of the carcinoembryonic antigen (CEA) with their limits of detection down to 40.6 and 94.9 pM, and thus reveal the great potential of these Sr₂YF₇:Ln³⁺ nanoprobes in cancer diagnosis.Sr₂YF₇, as an important matrix for trivalent lanthanide (Ln³⁺) ions to fabricate upconversion (UC) or downshifting (DS) phosphors, has been rarely reported. Herein, monodisperse and size-controllable tetragonal-phase Ln³⁺-doped Sr₂YF₇ nanoparticles (NPs) were synthesized via a facile thermal decomposition method. Upon excitation at 980 nm, UC luminescence properties of Sr₂YF₇:Ln³⁺/Yb³⁺ (Ln = Tm, Er) NPs were systematically surveyed. Particularly, after coating an inert Sr₂YF₇ shell, the UC luminescence intensities of Sr₂YF₇:Tm³⁺/Yb³⁺ and Sr₂YF₇:Er³⁺/Yb³⁺ NPs were enhanced by ~22 and 4 times, respectively. Furthermore, intense multicolor DS luminescence was also achieved in Ce³⁺/Tb³⁺ or Eu³⁺ doped Sr₂YF₇ NPs, with absolute quantum yields of 55.1% (Tb³⁺) and 11.2% (Eu³⁺). The luminescence lifetimes of ⁵D₄ (Tb³⁺) and ⁵D₀ (Eu³⁺) were determined to be 3.7 and 8.1 ms, respectively. By utilizing the long-lived luminescence of Ln³⁺ in these Sr₂YF₇ NPs, we demonstrated their application as sensitive heterogeneous time-resolved photoluminescence bioprobes to detect the protein of avidin and the tumor marker of the carcinoembryonic antigen (CEA) with their limits of detection down to 40.6 and 94.9 pM, and thus reveal the great potential of these Sr₂YF₇:Ln³⁺ nanoprobes in cancer diagnosis.

Electronic supplementary information (ESI) available: TEM images of Sr₂YF₇:Er³⁺/Yb³⁺ NPs with different sizes. EDX analysis results of Sr₂YF₇:Er³⁺/Yb³⁺ NPs. UCL spectra of NaYF₄:Er³⁺/Yb³⁺ NPs and Sr₂YF₇:Er³⁺/Yb³⁺@Sr₂YF₇ core/shell NPs. log-log plots of the UC emission intensity versus NIR excitation power density and schematic energy level diagrams of Tm³⁺ and Er³⁺ for Yb³⁺-sensitized UC processes. PL excitation spectra and lifetime of ⁵D₀ of Eu³⁺ in Sr₂YF₇ NPs at 10 K. PL decays of Sr₂YF₇:Ce³⁺/Tb³⁺ and Sr₂YF₇:Eu³⁺ NPs measured at RT. See DOI: 10.1039/c4nr02540g