LiYF4 nanocrystals (NCs) doped with 1% and 10% of Yb3+ and capped with oleic-acid were synthesized via a previously reported and modified co-precipitation method. Size, morphology, composition, and colloidal stability of these NCs are reported with data obtained from TEM, XRD, TGA/DSC, XRF, and zeta potential techniques. TEM analysis shows a monodisperse size distribution, with the nanocrystal size of ~20 nm. Optical characterization is described using data collected from UV-Vis-NIR absorption spectrophotometry and photoluminescence spectroscopy. The excellent luminescence in the NIR-II spectral region makes these NCs potential candidate for bioimaging 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 °C till 70 °C. These nanocrystals have a high potential to be used in optical cooling applications.
CdSexS1-x/ZnS quantum dots (QDs) can cover a broader spectral range than the commonly used CdSe/ZnS QDs and are potentially useful as biomarkers for tagging cell lines such as HeLa, A549, and MCF-7 due to their high photoluminescence intensity and stability in solution. So far, there have been few studies of colloidal CdSexS1-x/ZnS QDs that would simultaneously investigate changes in a) the molar composition of QD cores, and b) the shell thickness, as well as the effects of these changes on the photoluminescence and quantum yield properties of the QDs. CdSeyS1-y QDs and CdSexS1-x/ZnS core/shell QDs were synthesized via a previously reported and modified hot-injection procedure and via a telescoping one-pot synthesis based on the modified hot-injection procedure. Size, morphology, composition, and colloidal stability of these QD core/shell systems is reported with data obtained from TEM, XRD, TGA, DSC, DLS, and zeta potential techniques. Optical characterization is described using data collected from UV-Vis absorption spectrophotometry and photoluminescence spectroscopy.
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 (PbSe) or lead sulfide (PbS) 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.
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.
Phosphorus-free multiple-quantum-well lasers with In0.53Ga0.47As wells, In0.53Al0.2Ga0.27As barriers, and In0.53Al0.47As claddings have been fabricated as Fabry-Perot devices of different lengths and widths. Their current-voltage and light-current characteristics have been measured over a wide temperature range from 200 K down to 20 K. These data have been analyzed for experimental information on carrier freeze out, gain changes related to temperature, temperature-dependence of series resistance, and prospects for high-performance lasers operating at cryogenic temperatures.
Colloidal quantum dots (QDs) emitting in the visible spectrum are of interest for many biomedical applications, including bioimaging, biosensing, drug delivery, and photodynamic therapy. However, a significant limitation is that QDs typically contain cadmium, which is highly cytotoxic and makes prospects for their FDA approval for human treatment very unlikely. Previous work on biocompatible QDs has focused on indium phosphide and zinc oxide as alternative materials for QDs. However, these nanoparticles have also been shown to be cytotoxic. High-efficiency luminescent ZnTe-based QDs could be a reasonable alternative to Cd-containing QDs. We started our recent studies of ZnTe core, zinc chalcogenide shell QDs with synthesis, structural characterization, and investigation of optical properties of ZnTe/ZnSe colloidal QDs that displayed a blue-green photoluminescence under UV excitation. In this paper, the characteristics of ZnTe/ZnS QDs are compared to those of ZnTe/ZnSe QDs. We conclude that ZnTe/ZnS QDs are appealing candidates for various biomedical applications instead of the currently prominent alternative: cadmium-chalcogenide core QDs.
GaSb-based multiple-quantum-well lasers with In0.2Ga0.8Sb wells, Al0.35Ga0.65Sb barriers, and Al0.9Ga0.1Sb claddings have been fabricated as broad-area Fabry-Perot devices of dimensions 1000 μm × 800 μm. Their current-voltage and light-current characteristics, as well as emission spectra have been measured over a wide temperature range from 280 K down to 20 K. These data have been analyzed for experimental information on carrier freeze out, gain changes related to temperature, temperature-dependence of series resistance, and prospects for high-performance lasers operating at cryogenic temperatures.
Quantum dots (QDs) emitting in the visible are of interest for many biomedical applications, including bioimaging, biosensing, drug targeting, and photodynamic therapy. However, a significant limitation is that QDs typically contain cadmium, which makes prospects for their FDA approval very unlikely. Previous work has focused on InP and ZnO as alternative semiconductor materials for QDs. However, these nanoparticles have also been shown to be cytotoxic. High-efficiency luminescent ZnTe-based QDs could be a reasonable alternative to Cd-containing QDs. In this paper, we present preliminary results of our recent studies of ZnTe-based QDs, including their synthesis, structural characterization, and optical properties.
The human mouth is a host of a large gamut of bacteria species, with over 700 of different bacteria strains identified. Most of these bacterial species are harmless, some are beneficial (such as probiotics assisting in food digestion), but some are responsible for various diseases, primarily tooth decay and gum diseases such as gingivitis and periodontitis. Dental plaque has a complicated structure that varies from patient to patient, but a common factor in most cases is the single species of bacterium acting as a secondary colonizer, namely Fusobacterium nucleatum, while the actual disease is caused by a variety of tertiary colonizers. We hypothesize that destruction of a compound biofilm containing Fusobacterium nucleatum will prevent tertiary colonizers (oral pathogens) from establishing a biofilm, and thus will protect the patient from developing gingivitis and periodontitis. In this paper, we report on the effects of exposure of compound biofilms of a primary colonizer Streptococcus gordonii combined with Fusobacterium nucleatum to iron oxide nanoparticles as possible bactericidal agent.
Colloidal quantum dots (QDs) are of interest for a variety of biomedical applications, including bioimaging, drug
targeting, and photodynamic therapy. However, a significant limitation is that highly efficient photoluminescent QDs
available commercially contain cadmium. Recent research has focused on cadmium-free QDs, which are anticipated to
exhibit significantly lower cytotoxicity. Previous work has focused on InP and ZnO as alternative semiconductor
materials for QDs. However, these nanoparticles have been shown to be cytotoxic. Recently, we have synthesized high
quantum efficiency (exceeding 90%), color tunable MnSe/ZnSeS nanoparticles, as potentially attractive QDs for
biomedical applications. Additionally, the manganese imparts magnetic properties on the QDs, which are important for
magnetic field-guided transport, hyperthermia, and potentially magnetic resonance imaging (MRI). The QDs can be
further biofunctionalized via conjugation to a ligand or a biomarker of disease, allowing combination of drug delivery
with visual verification and colocalization due to the color tunability of the QDs.
Lanthanide fluoride colloidal nanocrystals offer a way to improve the diagnosis and treatment of cancer through the
enhanced absorption of ionizing radiation, in addition to providing visible luminescence. In order to explore this
possibility, tests with a kilovoltage therapy unit manufactured by the Universal X-Ray Company were performed to
estimate the energy sensitivity of this technique. La0.2Ce0.6Eu0.2F3 nanocrystals capped with polyethylene glycol of
molecular weight 6000 were synthesized, suspended in deionized water, and made tolerant to biological ionic pressures
by incubation with fetal bovine serum. These nanocrystals were characterized by dynamic light scattering, muffle
furnace ashing, and photoluminescence spectroscopy. Clonogenic assays were performed on the cells to assay the
cytotoxicity and radiotoxicity of the nanocrystals on the human pancreatic cancer cell line PANC-1, purchased from
ATCC.
Iron oxide colloidal nanoparticles (ferrofluids) are investigated for application in the treatment of cystic fibrosis lung
infections, the leading cause of mortality in cystic fibrosis patients. We investigate the use of iron oxide nanoparticles to
increase the effectiveness of administering antibiotics through aerosol inhalation using two mechanisms: directed
particle movement in the presence of an inhomogeneous static external magnetic field and magnetic hyperthermia.
Magnetic hyperthermia is an effective method for decreasing the viscosity of the mucus and biofilm, thereby enhancing
drug, immune cell, and antibody penetration to the affected area. Iron oxide nanoparticles of various sizes and
morphologies were synthesized and tested for specific losses (heating power). Nanoparticles in the superparamagnetic to
ferromagnetic size range exhibited excellent heating power. Additionally, iron oxide / zinc selenide core/shell
nanoparticles were prepared, in order to enable imaging of the iron oxide nanoparticles. We also report on synthesis and
characterization of MnSe/ZnSeS alloyed quantum dots.
Naturally occurring dysprosium is attractive as a neutron detector because of its high thermal neutron capture cross
section and high natural abundance. Neutron-induced transmutation of 164Dy results in production of stable isotopes of
holmium and erbium (the latter only at sufficiently high neutron fluxes), due to beta decays caused by nucleus
instability. This mechanism, unaffected by gamma radiation, can be used to unambiguously detect neutrons, without
having to discriminate against an accompanying gamma flux. Optically-enabled thermal neutron detection can be based
on significant differences in optical properties of Dy and Ho or Er, which allows to determine the relative fractions of
Dy, and Ho, and E in an irradiated sample. In our search for the most sensitive method of differentiating between Dy and
Ho residing in the same host material, we produced various Dy- and Ho-containing nanocrystals and uniformly dispersed
them in a PMMA polymer matrix. Optical properties of the nanocomposites were analyzed by means of absorption and
PL spectroscopy. We also report on neutron irradiation experiments with Dy-containing nanocrystals and our attempts to
optically detect neutron-induced conversion of Dy into Ho.
Iron oxide colloidal nanocrystals (ferrofluids) are investigated for application in the treatment of cystic fibrosis lung
infections, the leading cause of mortality in cystic fibrosis patients. We investigate the use of iron oxide nanocrystals to
increase the effectiveness of inhalation aerosol antibiotics therapy through two mechanisms: directed particle movement
in the presence of a static external magnetic field and magnetic hyperthermia. Magnetic hyperthermia is an effective
method for decreasing the viscosity of the mucus and biofilm thereby increasing drug, immune cell, and antibody
penetration to the affected area. Iron oxide nanocrystals of various sizes and morphologies were synthesized and tested
for specific losses (heating power) using frequencies of 111.1 kHz and 629.2 kHz, and corresponding magnetic field
strengths of 9 and 25 mT. Nanocrystals in the superparamagnetic to ferromagnetic size range exhibited excellent heating
power. Additionally, iron oxide-zinc selenide core-shell nanoparticles were prepared in parallel in order to allow
imaging of the iron oxide nanoparticles.
Lanthanide fluoride colloidal nanocrystals offer a way to improve the diagnosis and treatment of cancer through the
enhanced absorption of ionizing radiation, as well as providing visible luminescence. In order to explore this possibility,
cytotoxicity assays need to be performed on mammalian cells in vitro, to show minimum levels of biocompatibility for
future experiments. 20% lanthanum 60% cerium and 20% europium lanthanide fluoride nanocrystals were capped with
polyethylene glycol (PEG) of molecular weight 4000 and suspended in deionized water. These nanocrystals were
characterized by transmission electron microscopy, muffle furnace ashing, absorbance spectroscopy, dynamic light
scattering, and photoluminescence spectroscopy. Visible light microscopy and trypan blue staining was performed on the
cells to assay the cytotoxicity of the nanocrystal on the human astrocytoma line U-87 MG, purchased from ATCC.
The concept of detection of thermal neutrons using gadolinium oxide nanocrystals is explored. Gadolinium is an element
with by far the highest thermal neutron capture cross section among all stable isotopes. Colloidal synthesis of Gd2O3 nanocrystals, Gd2O3 nanocrystals doped with Ce, Gd2O3 nanocrystals doped with Eu, and Gd2O3 nanocrystals co-doped
with Ce and Eu is reported. The nanocrystals were characterized by transmission electron microscopy, energy-dispersive
X-ray spectroscopy, dynamic light scattering analysis, and steady-state UV-VIS optical absorption and
photoluminescence spectroscopy. Neutron detection has been modeled with MCNPX and confirmed in experiments with
Gd-containing nanocrystalline samples irradiated with 252Cf neutron source.
Cerium-doped lanthanum fluoride colloidal nanocrystals (NCs) offer a way to improve radiation therapy through the
enhanced absorption of high-energy photons. The use of Monte Carlo simulation allows the direct calculation of the
macroscopic dose enhancement factor (MDEF), a figure of merit for NC-enhanced radiation therapy. Our simulations of
brachytherapy using an Ir-192 source agree with previous work on the subject for gold NCs and show effectiveness of
LaF3:10%Ce NCs to be approximately 50% that of gold. Polyethylene-glycol-capped LaF3:10%Ce NCs were
synthesized, isolated, suspended in phosphate buffered saline (PBS), and characterized with transmission electron
microscopy, dynamic light scattering, photoluminescence spectroscopy, and absorption spectroscopy. LaF3:10%Ce NCs
were used in radiation dose enhancement experiments that involved an incoming 662 keV gamma flux from dual Cs-137
sources to test the mortality of Saccharomyces cerevisiae. At a small loading of 1.8 mg NC/g of PBS, the experiment did
not produce a measurable increased mortality. To understand the results, additional Monte Carlo simulations revealed
that the photon energy of 662 keV gamma rays is far from optimal, providing only a 4% increase in dose for a
concentration of 18 mg of NCs / g of PBS. Further simulations showed that the optimal photon energy for this technique
is 60 keV, tripling the absorbed dose for a concentration of 18 mg of NCs / g of PBS.
A novel concept for detection of thermal neutrons based on lanthanide halide nanocrystals containing gadolinium, an
element with by far the highest thermal neutron capture cross section among all stable isotopes, is presented. Colloidal
synthesis of GdF3 nanocrystals, GdF3 nanocrystals doped with Ce, and LaF3 nanocrystals doped with Gd is reported. The
nanocrystals were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy
(EDS), dynamic light scattering (DLS) analysis, and steady state UV-VIS optical absorption and photoluminescence
spectroscopy. Neutron detection has been confirmed in experiments with Gd-containing nanocrystalline material
irradiated with 252Cf neutron source.
Cerium-doped lanthanum fluoride colloidal nanocrystals offer a way to improve radiation therapy through the enhanced
absorption of high-energy photons. Lanthanum fluoride nanocrystals doped with 10% cerium and capped with oleic acid
were synthesized in anhydrous methanol as platelets 3-6 nm in diameter and 1-3 nm thick. The nanocrystals were
characterized by transmission electron microscopy and photoluminescence spectroscopy. Previously synthesized
lanthanum fluoride nanocrystals doped with 10% cerium and capped with hydroxyl were used in radiation dose
enhancement experiments that involved an incoming gamma flux from a 137Cs source and a FOX assay to measure
absorbed energy. Possibility for lanthanide ions to be released into solution under gamma irradiation and to interfere
with the assay was shown after the results were compared with the outcome of a similar previous experiment with the
Fricke dosimeter solution. Finally, increased cell mortality of S. cerevisiae under gamma irradiation was observed in the
presence of hydroxyl-capped lanthanum fluoride nanocrystals in the solution.
Lead-iodide-based PbI2, PbIOH and Pb3O2I2 nanocrystals were synthesized by various chemical and mechanochemical solution methods. The nanocrystals were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), dynamic light scattering (DLS), steady-state UV-visible optical absorption and photoluminescence spectroscopy, and by photoluminescence lifetime and quantum efficiency measurements. Scintillation tests were performed on the lead-iodide based material exposed to low-level gamma irradiation.
Colloidal synthesis of core/shell nanocrystals with cerium-doped lanthanum fluoride core and undoped lanthanum
fluoride shell, and of core/shell nanocrystals with hygroscopic cerium-doped lanthanum bromide core and undoped
lanthanum fluoride shell is reported. The nanocrystals were characterized by transmission electron microscopy (TEM),
energy dispersive X-ray spectroscopy (EDS), dynamic light scattering (DLS) analysis, steady state UV-VIS optical
absorption and photoluminescence spectroscopy, and by photoluminescence lifetime measurements. Scintillation tests
were performed on the cerium-doped lanthanum fluoride nanocrystalline material exposed to low-level gamma
irradiation.
Cerium-doped lanthanum fluoride colloidal nanocrystals offer a way to improve external radiation therapy through the
enhanced absorption of high energy photons, as well as through the emission of UV light in the presence of radiation,
providing a second cell killing mechanism. Lanthanum fluoride nanocrystals doped with 10% cerium were anhydrously
synthesized in methanol as platelets 10-12 nm in diameter and 4-6 nm thick. The nanocrystals were characterized by transmission electron microscopy, energy dispersive spectroscopy (EDS), and by steady state UV-visible optical absorption and photoluminescence spectroscopy. Using an incoming gamma flux from a 137Cs source and a Fricke dosimeter solution to measure absorbed energy, a 55% enhancement of absorbed dose was measured for a 1.2 mg/ml loading of nanocrystals over exposure range from one to four kiloroentgens.
Colloidal synthesis of cerium-doped lanthanum fluoride nanocrystals is reported. The nanocrystals were characterized by transmission electron microscopy, energy-dispersive X-ray spectroscopy,
steady-state UV-VIS optical absorption and photoluminescence (PL) spectroscopy, and by PL lifetime measurements. Cerium doping concentration was optimized for the maximum PL intensity. Radiation hardness of the synthesized nanocrystals was tested using a 137Cs 662-keV gamma source. Finally, scintillation was observed from the cerium-doped lanthanum fluoride nanocrystals exposed to
low-level gamma radiation.
Lead-iodide-based nanocrystals were synthesized by dissolution of commercial lead iodide powder in a coordinating
solvent, tetrahydrofuran, and subsequent re-crystallization after an optimum addition of methanol. The nanocrystals were
characterized by transmission electron microscopy, scanning electron microscopy, energy dispersive spectroscopy
(EDS), steady state UV-visible optical absorption and photoluminescence spectroscopy, and by photoluminescence
lifetime and quantum efficiency measurements. The radiation hardness of the synthesized material was tested using a
137Cs gamma source. Scintillation was observed from the lead-iodide based material exposed to low-level gamma
irradiation.
Semiconductor ring lasers show great promise for rotation sensing through the Sagnac effect of frequency shifting.
Ensuring a controlled unidirectional operation of ring lasers can greatly benefit this application. An S-section racetrack
design for semiconductor ring lasers was previously developed with the goal of favoring the waves traveling in a preselected
direction and suppressing the counterpropagating waves. However, that design turned out to be not as effective
as expected, with bistable behavior and directional switching over a wide range of pumping currents. We report on
design, fabrication and characterization of Y-junction S-section InAs/InGaAs/GaAs/AlGaAs quantum dot ring lasers
with improved unidirectionality. The new design suppresses the unwanted counterpropagating waves more effectively
than it was possible in the previous S-section-racetrack design.
Mid-infrared light-emitting diodes with InGaSb/AlGaAsSb triple-quantum-well active region have been integrated into
arrays of either 200×200 μm2 or 40×40 μm2 square pixels. Two generations of arrays have been designed, fabricated
and tested. The first, "sparse" 6×6 array provided valuable information on optimal electrode design and fabrication
parameters that was used in the design and processing of the second generation "dense" 11×11 array.
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