Sergei A. Ivanov

We have successfully synthesized near-infrared photoluminescent erbium-doped lithium yttrium fluoride nanocrystals using a facile coprecipitation approach. The nanocrystals are capped with oleic acid, enabling dispersion in nonpolar solvents such as toluene and cyclohexane. The relative amounts of yttrium and erbium precursors were adjusted during the synthesis to obtain different concentrations of Er between 1% and 15%. The composition and structure of the nanocrystals were studied via X-ray fluorescence spectroscopy and X-ray powder diffraction. The nanocrystals were optically characterized by extensive photoluminescence studies, including Stokes and anti-Stokes emission. When excited with 1.55-mu m light, the nanocrystals displayed strong anti-Stokes emission associated with the I-4(13/2) -> I-4(15/2) transition. These nanocrystals therefore have a high potential to be used in optical cooling applications with telecommunication-wavelength excitation.

Synthesized nanoparticles with strong luminescence in the second near-infrared window show great potential for applications in biomedical imaging and diagnosis. Nanoscale dimensions and tunable optical properties can enable nanoparticles to operate as fluorescent probes in the imaging of tumors and lymphatic tissues. Lanthanide-doped rareearth fluoride nanoparticles with photoluminescence tuned to the second near-infrared window can circumvent many of the issues currently limiting the clinical utility of fluorescence imaging technology and show promise as tools for the early detection of cancer. We report on the synthesis and characterization of colloidal LiYF4 nanoparticles doped with erbium. The nanoparticles were synthesized through a coprecipitation method using rare-earth chlorides, LiOH center dot H2O, and NH4F as precursors. 1-octadecene was used as a high-temperature solvent, and oleic acid was used as an organic capping agent. The reaction took place under the protection of nitrogen atmosphere. The size, morphology, and colloidal stability of the nanoparticles were determined using data obtained from transmission electron microscopy, dynamic light scattering, and zeta potential techniques. Optical characterization data were collected using NIR absorption spectroscopy and fluorescence spectroscopy. The Er3+-doped LiYF4 nanoparticles show NIR-II emission peaks at 1001 nm, 1490 nm, 1531 nm, and 1558 nm upon NIR-II excitation at 972 nm. The excellent luminescence in the NIR-II range makes them a strong candidate for bioimaging applications.

This paper reports on successful synthesis and comprehensive characterization of lithium yttrium ytterbium fluoride nanocrystals. The Yb content was varied between 1% and 10%. The nanocrystals emit in near-infrared, with the emission spectrum extending from 960 nm to 1060 nm when excited with the 900-nm light. Strong anti-Stokes photoluminescence was observed when using excitation wavelengths ranging from 1000 nm to 1020 nm. The temperature dependence of the Stokes and anti-Stokes photoluminescence was measured over the range from 10 °C till 70 °C. These nanocrystals have a high potential to be used in optical cooling applications.

We have successfully synthesized lithium yttrium fluoride (YLF) nanocrystals doped with ytterbium. The Yb content was varied between 1% and 10%. The nanocrystals emit in near-infrared, with the emission spectrum extending from 960 nm to 1060 nm when excited with the 900 nm light. Strong anti-Stokes photoluminescence was observed when using excitation wavelengths ranging from 1010 nm to 1020 nm. The temperature-dependence of the anti-Stokes photoluminescence was measured over the range from 10 degrees C till 70 degrees C. These nanocrystals have a high potential to be used in optical cooling applications.

Anti-Stokes photoluminescence from colloidal CdSeS/ZnS quantum dots (QDs) is observed. The QDs were inserted into the core of wider-bandgap SiO2/Si3N4/SiO2 structure by thin film deposition and confirmed as promising nanoemitters for laser cooling due to efficient anti-Stokes emission. The nanoemitters were optically pumped by semiconductor lasers coupled to the waveguides using free-space optics. A direct evidence of local optical cooling in the waveguide structure has been demonstrated with a luminescence thermometry based on the detection of photoluminescence signal phase change versus power of the pumping laser, using a lock-in amplifier.

Colloidal quantum dots (QDs) emitting in the near-infrared (NIR) spectrum are of interest for many biomedical applications, including bioimaging, biosensing, drug delivery, and photodynamic therapy. However, a significant limitation is that QDs are typically highly cytotoxic, containing materials such as indium arsenide (InAs), cadmium, or lead, which makes prospects for their FDA approval for human treatment very unlikely. Previous work on QDs in the NIR has focused on indium arsenide or cadmium chalcogenide cores coated with cadmium sulfide shells or zinc sulfide shells. Lead-based nanoparticles, such as lead selenide (PhSe) or lead sulfide (PhS) are also popular materials used for NIR emission. However, these nanoparticles have also been shown to be cytotoxic. Coating these Pb-based QDs with a biocompatible shell consisting of tin chalcogenides, such as tin sulfide (SnS) or tin selenide (TnSe), could be a reasonable alternative to improve their biocompatibility and reducing their cytotoxicity. In this paper, we report on our recent studies of PbSe-core QDs with Sn-containing shells, including synthesis, structural characterization, and investigation of optical properties. Characteristics of these QDs synthesized under different conditions are described. We conclude that their synthesis is challenging and still requires further work to avoid shell oxidation.