Temperature measurement in plasmonic traps is important because biological molecules and quantum emitters are sensitive to temperature. While other works have used ion pore currents, fluorescence emission variation, and fluorescent diffusion tracking to measure the temperature dependence of shaped nanoapertures in metal films, here we make use of a stable erbium (Er) containing NaYF4 nanocrystals that gives local temperature dependence. The local temperature variation is determined by a ratiometric analysis of the emission at different wavelengths.
Here we use optical trapping to isolate single Yb/Er-doped upconversion nanocrystals in plasmonic double nanohole apertures and show that the geometry of the aperture can be tuned to give high emission rate en- hancement. The double nanohole apertures show additional enhancement over the rectangular apertures that were previously demonstrated by our group, producing enough enhancement to observe emission at 400 nm and 1550 nm with 980 nm excitation—not seen in our group’s previous work with rectangular apertures. A facile method for tuning the geometry of double nanohole apertures by adjusting the plasma etching time in the colloidal lithography fabrication process is discussed. We find that a double nanohole with a cusp separation of 32 nm yields the greatest emission enhancement with multiple plasmonic resonances which enhance both the excitation and emission wavelengths. The emission enhancement for the DNH with 32 nm cusp separation was found to be a factor of 54, 44, and 31 greater than the rectangular apertures used in our group’s previous work, for wavelengths of 650 nm, 550 nm, and 400 nm. This result shows that double nanohole apertures can be tuned for emission enhancement as required by specific applications.
Single photon sources are desired for quantum computing and communication applications. Ideally, these sources would provide single photons on demand at the low-loss fiber optical communication wavelength of 1550 nm. Single Erbium ions provide a good candidate for such sources because they emit at the right wavelength and they are very stable, however, the challenges remain of isolating a single emitter, coupling its emission to optical fiber and enhancing its emission rate. Nanoaperture optical tweezers provide a pathway to solving these issues by trapping and identifying single emitters, enhancing their emission rate and providing efficient coupling to an optical fiber. Recently, we have made progress in each of these areas (trapping, enhancing and coupling), which will be reviewed in this talk.
Purpose: We present photon-counting computed tomography (PCCT) imaging of contrast agent triplets similar in atomic number (Z) achieved with a high-flux cadmium zinc telluride (CZT) detector.
Approach: The table-top PCCT imaging system included a 330-μm-pitch CZT detector of size 8 mm × 24 mm2 capable of using six energy bins. Four 3D-printed 3-cm-diameter phantoms each contained seven 6-mm-diameter vials with water and low and high concentration solutions of various contrast agents. Lanthanum (Z = 57), gadolinium (Gd) (Z = 64), and lutetium (Z = 71) were imaged together and so were iodine (Z = 53), Gd, and holmium (Z = 67). Each phantom was imaged with 1-mm aluminum-filtered 120-kVp cone beam x rays to produce six energy-binned computed tomography (CT) images.
Results:K-edge images were reconstructed using a weighted sum of six CT images, which distinguished each contrast agent with a root-mean-square error (RMSE) of <0.29 % and 0.51% for the 0.5% and 5% concentrations, respectively. Minimal cross-contamination in each K-edge image was seen, with RMSE values <0.27 % in vials with no contrast.
Conclusion: This is the first preliminary demonstration of simultaneously imaging three similar Z contrast agents with a difference in Z as low as 3.
Upconversion of sub-band-gap photons is a promising approach to increase the efficiency of solar cells. In this paper, we review the recent progress in upconverter material development and realization of efficient upconverter silicon solar cell devices. Current published record values for the increase in the short-circuit current density due to upconversion are 13.1 mA/cm2 at a solar concentration of 210 suns determined in a sun simulator measurement. This increase is equivalent to a relative efficiency enhancement of 0.19% for the silicon solar cell. Although this is a considerable enhancement by more than one order of magnitude from values published only a few years ago, further enhancement of the upconversion performance is necessary. To this end, we investigate theoretically the application of resonant cavity and grating photonic structures. Our simulation based analysis considers irradiance enhancement and modified density of photon states due to the photonic structures and their impact on the upconversion dynamics in β-NaYF4: 20%Er3+. It shows that an optimized grating can increase upconversion luminescence by a factor of 3 averaged over the whole structure in comparison to an unstructured reference with the same amount of upconverter material.
An effective strategy is presented to make spherical Ln3+ doped NaYF4 nanoparticles that show upconversion, with the
aim of deep-tissue optical imaging. Upconversion is the conversion of two or more low-energy photons into one of
higher energy, e.g. 980 nm to 545 and 680 nm and 980 nm to 800 nm. In order to avoid the formation of nanoparticles
with an aspect ratio, we developed a strategy in which subsequent shells were grown on spherical seed nanoparticles.
The last shell is undoped in order to improve the optical properties. In addition, a simple intercalation strategy involving
the oleate ligands on the surface has been developed to make the nanoparticles dispersible in aqueous solutions and
physiological buffers. Two-photon upconversion laser scanning microscopy (TPULSM) and two-photon upconversion
wide-field microscopy (TPUWFM) have been tested for their suitability in deep-tissue imaging with retention of lateral
and depth resolution (also called optical sectioning). TPULSM can be used up to ~ 600 μm deep, but takes inordinately
long times to acquire, which is due to the fact that the absorption cross section of Yb3+ is low, the quantum yield of the
upconversion process are << 1%, and the Ln3+ excited states are up to several hundreds of μs. Hence UCNPs in general are not very bright (i.e. large emitted photon flux). The TPUWFM seems more promising because acquisition times are
only several minutes, with depth profiling up to 400 μm. We show the first optical sectioning with this technique in the
brain of a mouse, through a thin shaved skull.
Photoresponsive nanocomposite organically modified silica films were prepared by solution sol-gel processing of
organo-silicon alkoxide compounds. Waveguiding at 488 and 514.5 nm proceeded with simultaneous self-inscription
and self-focusing. Light Induced self inscribed (LISI) waveguides were revealed by wet etching. Under certain
conditions, self-inscription exhibited optical beating or became chaotic, and filamentation was observed. Composite
waveguides of nanoplasmonic particles and rare earth doped nanoparticles were written by LISI.
Monolayer-stabilized nanoparticles of LaF3 and LaPO4 doped with the luminescent trivalent lanthanide ions Eu3+, Nd3+, Er3+, Pr3+, Ho3+, and Yb3+ have been prepared. These ions emit in the visible and in the near-infrared part of the electromagnetic spectrum. The ions Nd3+, Er3+ Pr3+, and Ho3+ are the main focus in this research because they show emissions in telecommunication windows. The Eu3+ ion is an excellent probe for the structural environment of the luminescent ion. It is shown that these lanthanide ions are incorporated in the inorganic host of the particles and that the particles are dispersable in organic solvents. The luminescent lifetimes of the ions are increased orders of magnitude compared to organic complexes, with values ranging from several microseconds for Pr3+ and Ho3+, up to about 200 μs for Nd3+, and 1 ms for Er3+. This increase in the luminescence lifetime is indicative of an effective shielding of the lanthanide ions from non-radiative decay of the excited state by the high-energy vibrations of the solvents and the coordinated organic ligands. A model is proposed to describe the non-exponential behavior of the lumienscence decay by quenching from outside the particle.
The performance and processing of passive and active polymeric integrated optic devices are described. Results obtained with several processed batches are compared, to evaluate the reproducibility of devices realized using polymer technology. The wafer-to-wafer differences in electro-optic switching properties were less than 10% for routinely fabricated devices, despite of the partially manual production process. Also, the stability of electro-optic polymers has been evaluated, both intrinsically and in devices. Using new polymers, with higher glass- transition temperatures, devices with long term stabilities up to at least 100 degree(s)C are expected in due time.
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