Efficient up-conversion in Yb:Er:NaT(XO4)(2) thermal nanoprobes. Imaging of their distribution in a perfused mouse

Abstract

Yb and Er codoped NaT(XO4)(2) (T = Y, La, Gd, Lu and X = Mo, W) disordered oxides show a green (Er3+ related) up-conversion (UC) efficiency comparable to that of Yb:Er:beta-NaYF4 compound and unless 3 times larger UC ratiometric thermal sensitivity. The similar UC efficiency of Yb:Er doped NaT(XO4)(2) and beta-NaYF4 compounds allowed testing equal subcutaneous depths of ex-vivo chicken tissue in both cases. This extraordinary behavior for NaT (XO4)(2) oxides with large cutoff phonon energy (h omega approximate to 920 cm(-1)) is ascribed to F-4(9/2) electron population recycling to higher energy (4)G(11/2) level by a phonon assisted transition. Crystalline nanoparticles of Yb:Er:NaLu(MoO4)(2) have been synthesized by sol-gel with sizes most commonly in the 50-80 nm range, showing a relatively small reduction of the UC efficiency with regards to bulk materials. Fluorescence lifetime and multiphoton imaging microscopies show that these nanoparticles can be efficiently distributed to all body organs of a perfused mouse.