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. Author manuscript; available in PMC: 2013 Sep 25.
Published in final edited form as: ACS Nano. 2012 Sep 4;6(9):8280–8287. doi: 10.1021/nn302972r

Figure 2.

Figure 2

Optical characterizations of (NaYbF4:0.5% Tm3+)/CaF2 core/shell UCNPs (hexane suspensions). a) upconversion photoluminescence spectrum under laser excitation at 975 nm, b) photographic images of cuvettes with suspensions of the core and the core/shell nanoparticles under laser excitation at 975 nm, c) decays of PL at 802 nm for the α-NaYbF4: 0.5% Tm3+ core and the α-(NaYbF4:0.5% Tm3+)/CaF2 core/shell nanoparticles, and d) upconversion PL spectra of 27-nm α-(NaYbF4:0.5% Tm3+)/CaF2 core/shell nanoparticles and 100-nm β-NaYbF4:0.5% Tm3+ (hexagonal) nanoparticles, when excited by a 975-nm CW diode laser at a power density of ~ 0.3 W/cm2. The insets in Figures 2a and d show the absorption spectra of UCNPs (normalized at the PL excitation wavelength for the 2F7/2→ 2F5/2 transition of Yb3+ ions).