2 research outputs found
NIR to VUV: Seven-Photon Upconversion Emissions from Gd<sup>3+</sup> Ions in Fluoride Nanocrystals
Here
we show that a near-infrared (NIR) diode laser is capable
of generating vacuum ultraviolet (VUV) emissions in fluoride nanocrystals
through photon upconversion (UC) processes. By using Yb<sup>3+</sup> and Tm<sup>3+</sup> as sensitizers, we successfully obtained the
VUV photons with the energy exceeding 6 eV in YF<sub>3</sub>: Yb,
Tm, and Gd nanocrystals. The seven photon UC fluorescence from the <sup>6</sup><i>G</i><sub><i>J</i></sub> → <sup>8</sup><i>S</i><sub>7/2</sub> transitions of Gd<sup>3+</sup> ions and the possible VUV UC mechanism were reported along with
the calculation of the branching ratio under different pumping power
excitation. Practically, it offers a promising solution for VUV light
generation without cryogens and expensive instrumentations. Fundamentally,
the extremely high-order UC processes will intrigue great interest
in exploring unusual high-energy radiative transitions in rare earth
ions
Microgel-Based Thermosensitive MRI Contrast Agent
Monitoring subtle temperature changes
noninvasively remains a challenge for magnetic resonance imaging (MRI).
A temperature-sensitive contrast agent based on thermosensitive microgel
is proposed and synthesized using a manganese tetraÂ(3-vinylphenyl)
porphyrin core reacting with <i>N</i>-isopropylacrylamide
(NIPAM) or <i>N</i>-isopropylmethacrylamide (NIPMAM) monomers
and <i>N</i>,<i>N</i>′-methylenebisÂ(acrylamide)
(MBA) cross-linkers. The volume of the NIPAM-incorporated microgel
(<b>M-1</b>) decreased sharply around its lower critical solution
temperature (LCST, 29–33 °C), whereas the volume of the
NIPMAM-incorporated microgel (<b>M-2</b>) decreased gradually.
MR longitudinal relaxivity (<i>r</i><sub>1</sub>) enhancement
(44%) was obtained for <b>M-1</b>, while the corresponding change
for <b>M-2</b> was much smaller. <b>M-1</b> was further
optimized in synthesis without an MBA cross-linker to obtain <b>M-3</b> which showed a 67% increase in <i>r</i><sub>1</sub> around its LCST. Our results suggested that the longitudinal
relaxivity is strongly modulated by microgel volume change around
the LCST, leading to a significant increase in <i>r</i><sub>1</sub>. This novel thermally sensitive microgel could potentially
be applied to monitor small temperature changes using MRI methods