Fig 1.
Comparison of up-conversion properties of DMo/DW and β-NaYF4.
RT UC characteristics of Yb:Er:DMo/DW in comparison to Yb:Er:β-NaYF4 upon cw DL excitation with 4 W/cm2 of light density. a) UC spectral distribution of 25at%Yb:5at%Er:NaLu(MoO4)2 synthesized by solid state reaction. (b) UC spectral distribution of HT 10at%Yb:1at%Er:β-NaYF4. Indicated multiplets are those emitting to the ground 4I15/2 one. Note that for a given material the intensity of blue, green and red UC, although arbitrary, is in the same scale. (c) Evolution of the green UC efficiency of Yb:Er:NaY(WO4)2 as a function of Yb and Er concentrations. (d) Evolution of the green UC efficiency of HT Yb:Er:β-NaYF4 as a function of Yb and Er concentrations. (e) Maximum green UC efficiencies achieved for 15at%Yb:1at%Er:NaT(XO4)2 (shorten as NaTX) synthesized by solid state reaction (●) or HT (▲) methods, relative to HT 7.5at%Yb:0.5at%Er:β-NaYF4 (line). (f) Comparison of NaY(WO4)2 and β-NaYF4 thermometric properties.
Fig 2.
Simulation of subcutaneous up-conversion detection.
(a) Images of the UC emission of the reference 7.5at%Yb:0.5%Er:β-NaYF4 and of 15%Yb:1%Er:NaLu(MoO4)2 compounds lying below several tissue thicknesses of ex-vivo chicken breast. The images were continuously excited with 3 W/cm2 of light density. (b) Semi-logaritmic representation of the green UC intensity as a function of the thickness of the ex-vivo chicken breast tissue tested with different UC sources: 7.5at%Yb:0.5at%Er:β-NaYF4 (HT, ■), 25at%Yb:5at%Er:NaY(WO4)2 (solid state reaction, □), 15at%Yb:1at%Er:NaLu(MoO4)2 (solid state reaction, ×), and 15at%Yb:1at%Er:NaLa(WO4)2 (HT, ▲). (c) Optical attenuation of ex-vivo chicken breast tissue.
Fig 3.
Characterization of sol-gel nanoparticles.
Properties of sol-gel synthesized Yb:Er:NaLu(XO4)2 UCNPs. (a,b) TEM images of 25at%Yb:1at%Er:NaLu(MoO4)2 sol-gel products after 4h calcination at 600°C. (c) HRTEM image of highly crystalline 15at%Yb:1at%Er:NaLu(WO4)2 rounded NPs with ≈20 nm of diameter. (d) Selected area of the HRTEM image. Observed lattice fringe distances are 0.305 nm, which matches the (112) interplanar spacing of NaLu(WO4)2. (e) Fast Fourier transform of the above image showing particle crystallinity. (f) pXRD scans of 25at%Yb:5at%Er:NaLu(MoO4)2 sol-gel NPs as a function of calcination at increasing temperature for a 12 h period. (g) Evolution of the green UC intensity of 25at%Yb:5at%Er:NaLu(MoO4)2 sol-gel NPs as a function of calcination at increasing temperature for a 12 h period. (h) Relationship between green UC efficiency of 25at%Yb:5at%Er:NaLu(MoO4)2 sol-gel NPs and their crystalline domain size.
Fig 4.
DSL characterization of NP size.
Hydrodynamic particle size distribution in water of 25at%Yb:5at%Er:NaLu(MoO4)2 sol-gel products obtained after 6h of 600°C calcination and 12 min of processing with ultrasounds.
Fig 5.
Macroscopic up-conversion characterization of perfused mouse organs.
UC emission from organs of a mouse after perfusion with sol-gel synthesized 25at%Yb:5at%Er:NaLu(MoO4)2 NPs.
Fig 6.
FLIM assessment of up-conversion from mouse perfused sol-gel nanoparticles.
Combined fluorescence intensity and FLIM analyses of tissue sections after perfusion with sol-gel synthesized 25at%Yb:5at%Er:NaLu(MoO4)2 NPs. Intensity images of UCNPs at λEXC = 973 nm, λEMI = 530±43 nm (a, g), and corresponding fluorescence lifetime distributions represented by the phasor transform in polar coordinates (b, h). The FLIM images (c, i) show the localization of the pixels enclosed in the red-circled cursor. The lung (d) and liver (l) sections in which the particles are found were imaged at λEXC = 900 nm and λEMI = 445±20 nm. The fluorescence lifetime distributions associated to the tissues are represented by the phasors enclosed by the red-circled cursor in (e) and (m). Independently on the source of the tissue signals, SHG (lung) or autofluorescence (liver), UCNPs fluorescence lifetime distributions are clearly distinguishable from that of the tissues in which the particles are trapped. Images are shown in pseudo-color scales.
Fig 7.
Bi and three dimensional micrographs of sol-gel nanoparticles perfused in mouse organs.
Composite images showing tissue autofluorescence (red) and up-conversion of sol-gel synthesized 25at%Yb:5at%Er:NaLu(MoO4)2 NPs perfused into mouse organs (green). Heart (a,b), lung (c), kidney (d), liver (e) and brain (f). Composite images were obtained from 3x3 tile scans for a total area of 1190 x1190 μm2. A 3D rending of a z-stack of 38 planes of one tile scan acquired at 2 μm step size is also shown for the heart sample (b). Images are shown in pseudo-color monochromatic scales.
Fig 8.
Physical model of up-conversion.
Energy level diagram of the Yb-Er excitation and energy transfer mechanisms giving rise to green UC in DMo/DW compounds. Note that the phonon assisted Yb3+(2F5/2→2F7/2)+ħω(≈923 cm-1)-Er3+(4F9/2→2G11/2) transition bleaches the red UC emission. This electron recycling is further illustrated in the right hand inset.
Fig 9.
Thermal up-conversion efficiency change.
Thermal evolution comparison of the integrated 2H11/2+4S3/2 green UC emission intensity from 15at%Yb:1at%Er:NaY(WO4)2 (○) and 7.5at%Yb:0.5at%Er:NaYF4 (■) compounds. In both cases the intensity at 300 K has been normalized to one.